Descriptive Mineralogy
Descriptive Mineralogy by William Shirley Bayley (1917). Full text and reference in the Mountain Man Mining Library.
Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.
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Descriptive Mineralogy
Mineralogy
By
William Shirley Bayley, Ph.D.
PBOFXBSOR OP GEOLOGY. T7NTVTBBSITY OF ILLINOIS AUTHOR OF "BLEMENTABY CBYSTAI,IX)OKAPHX "
"WITH TWO HTCnSTDKED AND SIXTY-EIGHT ILLUSTRATIONS
D. Appleton And Company
New York And London
Copyright, 1917, By D Appleton And Company
To My Helper
My Wife
This Book Is Dedicated
Preface
THE following pages are presented with the purpose of affording students a comprehensive view of modern mineralogy rather than a detailed knowledge of many minerals The -minerals selected for description are not necessarily those that are most common nor those that occur in greatest quantity The list includes those that are of scientific interest or of economic importance, and, in addition, those that illustrate some principle employed in the classification of minerals. The volume is not a reference book. It is offered solely as a textbook It does not pretend to furnish a complete discussion of the mineral kingdom, nor a means of determining the nature of any mineral that may be met with The chapters devoted to the processes of deter- minative mineralogy are brief , and the familiar " key to the determina- tion of species " is omitted In place of the latter is a simple guide to the descriptions of minerals to be found in the body of the text. For more complete determinative tables the reader is referred to one of the many good books that are devoted entirely to this phase of the subject. In the descriptions of the characteristic crystals of minerals both the Naumann and the Miller systems of notation are employed, the former because of its almost general use in the more important refer- ence books and the latter because of its almost universal use in modern crystallography investigations The student must be familiar with both notations It is thought that this familiarity can be best acquired by employing the two notations side by side
In preparing the descriptive matter the author has made extensive use of Hintze's Handbuch der Mvrwralogie. The figures illustrating crystal forms are taken from many sources. A few illustrations have
viii PREFACE
been made especially for this volume. Figures copied to illustrate special features are accredited to their authors. The statistics are mainly from the Mineral Resources of the Umted States They are given for the year 1912 because this was a more nearly normal year in trade than any that has followed
The author is under obligation to the McGraw-Hill Book Company for permission to reproduce a number of illustrations originally published in his Elements of Crystallography, and also for the use of the original engravings m making the plates for Figures n, 33, 71, 90, no, 114, 115, 118, 160, 191, 194, 224, 240, and 248.
W. S. Bayley.
Contents Part I
General Chemical Mineralogy
Chapter Page
I THE COMPOSITION AND CLASSIFICATION OF MINERALS i
Ii The Formation Of Minerals And Their Alterations 17
Part Ii Descriptive Mineralogy
Iii Introduction— The Elements 36
Iv The Sulphides, Tellurides, Selenides, Arsenides, And
Antimonides 68
V THE SULPHO-SALTS AND SULPHO-FERRITES. Il6
Vi The Chlorides, Bromides, Iodides, And Fluorides. 134
Vii The Oxides 146
Viii The Hydroxides 179
Ix. The Aluminates, Ferrites, Chromites And Manganttes 195
X. The Nitrates And Borates 205
Xi The Carbonates 212
Xii The Sulphates 236
Xih The Chromates, Tungstates And Molybdates 253
Xiv The Phosphates, Arsenates And Vanadates. 261
Xv The Columbates, Tantalates And Uranates 293
Xvi The Silicates The Anhydrous Orthoselicates . 300
Xvii The Silicates The Anhydrous Metasilicates . 359
Xviii The Silicates The Anhydrous Trimetasilicates. . 408
Xix The Silicates The Anhydrous Polysilicates . 426
Xx The Silicates The Hydrated Silicates . 441
Xxi The Silicates The Titanates And Tttanosilicates. .. 461
Part Iii Determinative Mineralogy
XXII GENERAL PRINCIPLES OF BLOWPIPE ANALYSIS. 467 XXIH CHARACTERISTIC REACTIONS OP THE MORE IMPORTANT ELEMENTS
AND Aero RADICALS, , . 483
Contents
Appendices
Chapter Page
I GUIDE TO THE DESCRIPTIONS or MINERALS 495 II LIST or THE MORE IMPORTANT MINER AIS ARRANGED ACCORD- ING TO THEIR PRINCIPAL CoNSTrrui'Nib 515
Iii List Op Minerals Arranged According To Their Crys-
Tallization 521
Iv List Of Reference Books 527 Index 529
List Of Illustrations
Figure Page
1 Sodium fluosihcate crystals ... 14
2 Potassium fluosihcate crystals 14
3 Cross-section of symmetrical vein 21
4 Cross-section of vein in green porphyry 24
5 Dionte dike cutting granite gneiss 26
6 Vein in Griffith mine 27
7 Vein forming original ore-body, Butte, Mont 27
8 Druse of Smithsonite 28
9 Geodes containing calcite 29
10 Alteration of ohvine into serpentine 31
11 Etch figures in cubic face of diamond 38
12 Crystal of diamond with rounded edges and faces 38
13 Octahedron of diamond 38
14 Principal "cuts" of diamonds 42
15 Premier diamond mines m South Africa 43
1 6 The Cullman diamond 43
17 Gems cut from Culhnan diamond . 44
1 8 The Tiffany diamond 44
19 Sulphur crystals 47
20 Distorted crystal of sulphur. ... 47
21 Copper crystal 53
22 Crystal of copper from ELeweenaw Point 53
23 Plate of silver from Comagas Mine, Cobalt 57 24. Octahedral skeleton crystal of gold with etched faces 58
25 Iron meteonte 65
26 Widmanstatten figures on etched surface of meteonte 66
27 Realgar crystal . . 70
28 Stibrute crystal 72
29 Galena crystal 81
30 Galena crystals . 82
31 Chalcocite crystal 85
32 Complex chalcocite twin 85
33 Tetrahedral crystal of sphalerite 88 34. Sphalerite crystal , 88
35 Sphalerite octahedron . 88
36 Greenockite crystal . . 91
37 Pyrrhotite crystal. 92
xu LIST OF ILLUSTRATIONS
Figure Page
38 Cinnabar crystals 98
39 Group of pyrite crystals in which the cube predominates 102
40 Pyrite crystals on which 0(111) predominates 102
41 Pyrite crystal 102
42 Group of pyrite crystals 103
43 Pyrite mterpenetration twin 103
44 Marcasite crystal no
45 Marcasite crystal with forms as indicated m Fig 44 no
46 Twin of marcasite no
47 Spearhead group of marcasite no
48 Arsenopynte crystals 112
49 Crystal of pyrargyrite ng
50 Crystal of proustite 119
51 Bournonite crystal 121
52 Bournonite fourlmg twinned 121
53 Enargite crystal 123
54 Stephanite crystal 125
55 Tetrahednte crystal I28
56 Chalcopynte crystal I3I
57 Chalcopynte 131
58 Chalcopynte twin 13!
59 Hopper-shaped cube of halite , 135
60 Group of fluonte crystals from Weardale Co 139
6 1 Crystal of fluonte !4O
62 Interpenetration cubes of fluonte, twin- 140
63 Photographs of snow crystals 147
64 Zmcite crystal !0
65 Hematite crystals
66 Corundum crystal
67 Corundum crystal
68 Corundum crystal
69 Quartz crystal exhibiting rhombohedral symmetry 159
70 Ideal (A) and distorted (B) quartz crystals . 159
71 Etch figures on two quartz crystals of the same form , 160
72 Group of quartz crystals , jgo
73 Tapenng quartz crystal X5X
74 Quartz crystal , ufa
75 Supplementary twins of quartz. , ,162
76 Quartz twinned I0*3
77 Cassitente crystal , . . 169
78 Cassitente crystal ,
79 Cassitente twinned j$g
80 Rutile crystals 172 81. Rutile eightluig twinned , . , 2
List Op Illustrations
Figure
82 Rutile twinned . . 172
83 Rutile cycbc sixling twinned
84 Rutile twinned
85 Anatase crystal I77
86 Anatase crystal I77
87 Brookite crystals I73
88 Brucite crystal f !32
89 Limonite stalactites in Silverbow mine. . , 184
90 Botryoidal hmorute . . jg
91 Pisohtic bauxite from near Rock Run . 187
92 Diaspore crystals , I9O
93 Mangamte crystal . . I92
94 Group of prismatic mangamte crystals 192
95 Mangamte crystal twinned . . 193
96 Spinel twin . . ig5
97 Spinel crystal . 196
98 Magnetite crystal . 198
99 Chrysoberyl crystal 203
100 Chrysoberyl twinned . . 203
101 Chrysoberyl pseudohexagonal sixling . 203
102 Hausmanmte . . 204 103. Borax crystal . . 207
104 Colemamte crystals 209
105 Boracite crystal 211
106 Calcite crystal . 214
107 Calcite crystals 214
108 Calcite crystals 214
109 Calcite . 214
no Prismatic crystals of calcite 215
in Calcite . 215
112 Calcite twin and polysynthetic trilling. 215
113 Calcite 216
114 Artificial twin of calcite , 216
115 Thin section of marble viewed by polarized fight. . 216
1 16. Aragonite crystal 224
117. Aragonite twin 224
118 of aragomte 224
119 Withente twinned . 226
120. Cerussite crystal . . 227
121. Cerussite twinned . , 227
122. Cerussite trilling twinned 227
123. Radiate groups of cerussite on galena . . -228
124. Dolomite crystal. . - 229
125. Group of dolomite crystals. . 230
X1V List Of Illustrations
Figure Page
126 Malachite crystal .232
127 Azurite crystals 233
128 Trona crystal 235
129 Gayhissite crystal 235
130 Glauberite crystal 237
131 Thenardite crystal 237
132 Thenardite twinned 237
133. Bante crystals 239
134. Bante crystals 240
135. Celestite crystals 241 136 Anglesite crystal 243 137. Anglesite crystal 243 138 Anglesite crystal 243
139. Gypsum crystals 247
140. Gypsum twinned 247
141. Gypsum twinned 248
142. Epsomite crystal 250
143. Hanksite crystal 252
144. Crocoite crystals 253
145. Scheelite crystal . 255
146. Scheelite crystal 255
147 Wulfemte crystal 257
148 Wulfemte crystal , . 257
149 Wolframite crystal 250 150. Monazite crystal , 264
151 Xenotime -crystals 265
152 Apatite crystal , 267
153 Apatite crystal . . 267 154- Vanadimte crystal . 262 155. Skeleton crystal of vanadmite . .272
156 Amblygomte crystal ,
157. Lazulite crystals , . , . 26
158 Olivemte crystal. , 27
159 Skorodite crystal 286
160 Radiate wavelhte on a rock surface . , , 287 161. Columbite crystals . ,
162 Samarskite crystals . . . , . 297
163 Olivme crystals , , 3P3
164 Willemite crystal , , 3O7
165 Phenacite crystal , 3Og 166. Garnet crystal (natural size) . 3IO
167 Garnet crystals ,, , , .310
168 Garnet crystal , 31O
16) Nephehue crystal, , I
List Of Illustrations
Page
. ,
170 Zircon crystals .317
171 Zircon twinned „.
172 Thorite crystal 3Ip
173 Andalusite crystals ,2O
174 Topaz crystals 32-
175 Topaz crystal 323
176 Topaz crystal ,24
177 Danbunte crystal 325
178 Zoisite crystal
179 Epidote crystal 2g 1 80 Epidote crystals 328
181 Chondrodite crystal 333
182 Datolite crystal 334
183 Staurolite crystal 337
184 Staurolite crystal twinned 337
185 Staurolite crystal twinned 33-7 1 86 Sodalite mterpenetration twin of t\vo dodecahedrons 340 187 Prehmte crystal - 344 1 88. Axinite crystal 346
189 Axmite crystal . 346
190 Dioptase crystal 347
191 Percussion figure 348
192. Biotite crystal 349
193. Biotite twinned about a plane . 349
194 Etch figures 356
195 Muscovite crystal 356
196 Beryl crystals .. 360
197 Beryl crystals . . 360 198. Cross-section of pyroxene , 363
199 Enstatite crystal. . 366
200 Wollastomte crystal . 368
201. Augite crystal . . 37*
202. Augite twinned . 371
203 Interpenetration twin of augite . 371
204 Diopside crystals , . 372 205, Hedenbergite crystal 373 206* Acute crystal , 3 76 207. Spodumene crystal. . . 379 208 Rhodonite crystals 3&> 209;. Ampibole crystals 34 210. Kyanite crystals 394 211 Bladed kyanite crystals in a micaceous quartz schist 395
212. Calarmne crystals , 30
213. Orthoclase crystals . . . , , 410
xvi LIST OP ILLUSTRATIONS
Figure Page
215 Carlsbad mterpenetration twins of orthoclasc 410
216 Contact twin of orthoclase according to the Carlsbad law 4IO
217 Baveno twins of orthoclase 411
218 Manebach twin of orthoclase 411
219 Section of mirocline viewed between crossed nicols 4x4
220 Adulana crystal 414
221 Albite crystals 419
222 Albite twinned 419
223 Albite twinned 419
224 Twinning stnations on cleavage piece of ohgoclasc 420
225 Albite twins with the crystal axis 420
226 Position of "rhombic sections" in albite . 420
227 Diagram of crystal of tnclimc feldspar f 420
228 Potash-oligoclase crystal 422
229 Scapohte crystals 424
230 Chntonite twinned according; to the mica law 427
231 Cknochlore crystal 430
232 Clmochlore twinned according to mica law 430
233 Chnochlore with same forms as m Fig 232 430
234 Clmochlore twinned according to mica law 430
235 Pennimte crystal 430
236 Pennimte crystal twinned 430
237 Vesuviamte crystals . 433 238. Tourmaline crystals 436
239 Tourmaline crystals 436
240 Cooling crystal of tourmaline 436
241 Cordiente crystal . . , 439
242 Apophylhte crystals 444
243 Heulandite crystal , , 447
244 Heulandite, var beaumontJte . . 447
245 Philhpsite mterpenetration twin , , 448
246 Phillipsite , 448
247 Harmotome fourling twinned like pmllipsite . 449
248 Sheaf-like aggregates of stilbite , . 450
249 Laumontite crystal 452
250 Divergent groups of scolecite crystals 453
251 Scoleate crystal , 453
252 Natrohte crystals , , . 434 253. Thomsomte crystal . , ... 456
254 Chabazite crystal t 47
255 Chabazite mterpenetration twin . . 457 256. Phacohte with same form as in Fig 254 . 457 257 Analate crystal , t 4
List Of Illustrations
Figure Page
258 Analcite crystal . , , . , 4-9
259 Ilmemte crystal 463
260 Titanite crystal 4g4
261 Titanite crystal 44
262 Titanite crystal 454
263 Simple blowpipes 4gg
264 Bellows for use with blowpipe 468
265 Candle flame showing three mantles 47o
266 Reducing flame 4yZ
267 Oxidizing flame 4r 268. Props and position of charcoal 45
Descriptive Mineralogy
Part I General Chemical Mineralogy
Chapter I
The Composition And Classification Of Minerals
Definition of Mineral. — A mineral is a definite inorganic, chem- ical compound that occurs as a part of the earth's crust. It possesses characters which are functions of its composition and its structure. Most minerals are crystallized, but a few have been found only in an amorphous, colloidal condition. These are regarded as gels, or solid colloids.
The most essential feature of a mineral is its chemical composition, since upon this are believed to be dependent all its other properties.
Chemical Substances Occurring as Minerals.— The chemical substances found native as minerals may be classed as elements and compounds The latter comprise chlorides, fluorides, sulphides, oxides, hydroxides, the salts of carbonic, sulphuric, phosphorus, arsenic, anti- mony and silicic acids, a large series of complicated compounds known as the sulpho-salts, a few derivatives of certain metallic acids— the aluminates and the ferrites— besides other salts of rarer occurrence, some simple and others exceedingly complicated, and possibly many solid solutions of gels or of a gel and a crystalloid. In some of these classes all the compounds are anhydrous. In others, some groups are anhydrous while the members of other groups contain one or more molecules of water of crystallization.
The sulphides, chlorides and fluorides are derivatives of EfeS, HC1, and ifeFs, respectively. They may be regarded as having been pro- duced from these compounds by the replacement of the hydrogen by metals. Illustrations: CuaS, CuS, NaCl, CaF2.
2 General Chemical Mineralogy
The hydroxides and the oxides may be looked upon as derivatives of water, the hydroxides through the replacement of one atom of hydrogen by a metal, and the oxides through the replacement of both hydrogen
/Oh
atoms The mineral, bructte, according to this view is Mg/ ,
H(Oh) X)H
derived from \ by replacement of two hydrogen atoms in two H(OH)
molecules of water by one atom of Mg Cuprite is >0, and tenonte
Cu/
CuO, the former derived by replacement of each atom of hydrogen m one molecule of water by an atom of Cu, and the latter by replacement of the two hydrogens by a single Cu
The salts of carbonic acid (H2COs) are the carbonates, those of sul- phuric acid (HaSO*) the sulphates, those of orthophosphoric acid (HsP04) the phosphates, those of orthoarsemc acid (HsAsO the arsen- ates, those of orthoantimomc acid (HaSbO-i) the antimonates and those of the silicic acids, the silicates There are, in addition, a few arsenites and antimonites that are salts of arsemous (HsAsOa) and antimonous (H3Sb03) acids
The principal silicic acids whose salts occur as minerals are normal silicic acid (H4Si04), metasihcic acid (HaSiOj), and tribilicic acid (HiSiaOs) The metasihcic and the tribihcic acids may be regarded as normal silicic acid from which water has been abstracted, m the same way that pyrosulphuric acid is ordinary sulphuric acid less H20, thus: 2H2SO*- H20 H2S207
(HO)4Si-H20=H2Si03, metasihcic acid 3(HO)4Si-4H20=H4Si30, tnsihcic acid.
Faydite is Fe2Si04, wollastonite, CaSiOs, and ortkoctase, KAlSisOs- The alummates and ferntes may be regarded as salts of the hypothet- ical acids AIO(OH) and FeO(OH), both of which exist as minerals, the first under the name dtaspore and the second under the name
yO— A10
goethite. Spinel is the magnesium aluminate, Mg<f .(MgAfeO*),
and magnofernte the corresponding ferrate MgFe204. The very com-
X)— FeO mon mineral magnetite is the iron ferrate Fe<; , or FesO*, In
this compound the iron is partly in the ferrous and partly in the ferric state.
Composition And Classification 3
There are other minerals that differ from those of the classes above mentioned in containing more or less water of crystallization These are usually separated from those m which there is no water of crystal- lization under the name of hydrous salts
Besides the classes of minerals considered there are others which appear to be double salts, m which two substances that may exist independently occur combined to form a third substance with prop- erties different from those of its components Cryolite, sNaF-AlFa or NasAlFe, is an example The sulpho-salts furnish many other examples
Further, a large number of minerals are apparently isomorphous mixtures of several compounds These are homogeneous mixtures of two or more substances that crystallize with the same sym- metry, and, consequently, that may crystallize together Their physical properties are continuous functions of their chemical com- positions. Other minerals are apparently solid solutions in one an- other of simple crystallizable salts, of gels, of gels and salts, and of gels and adsorbed substances Among these are some of the commoner silicates.
Determination of Mineral Composition. — Since the properties of minerals are functions of their chemical compositions, it is important that their compositions be known as accurately as possible. It is necessary in the first place that pure material may be secured for study Pure material is most easily secured by making use of the differences in density exhibited by different compounds The mineral to be studied is pounded to a powder, sifted through a bolting doth sieve and shaken up with one of the heavy solutions employed in determining specific gravities. When the solution is brought to the same density as that of the mineral under investigation all material of a higher specific gravity will sink. The material with a density lower than that of the solu- tion will rise to the surface Material with a specific gravity identical with that of the solution will be suspended in it If the mixing is done in a separating funnel of the proper type, the materials may be drawn off into beakers in the order of their densities, and thus the pure mineral may be separated from the impurities that were originally incorporated with it. After the purity of the substance is assured by examination under the microscope, it is ready for analysis
The composition of the purified material is determined by the ordinary methods of chemistry known as analysis and synthesis.
In analysis the compound is broken into its constituent parts and these are weighed, or it is decomposed and its constituents are trans-
4 General Chemical Mineralogy
formed into known compounds which are weighed From the weights thus obtained the proportions of the components m the original sub- stance may be easily calculated if the weight of the original substance be known
In synthesis the compound is built up from known elements or compounds
If the mineral caicite (CaCOs) is decomposed by heat into lime (CaO) and carbonic acid gas (CCte), or if its components are trans- formed into the known compounds CaSCU and KaCOj, the process is analysis If the known substance CCfe is allowed to act upon the known substance CaO and the resulting product is a substance possess- ing all the properties of caicite, the process is synthesis.
Analytical Methods.— The analytical methods made use of in mineralogy are (i) the ordinary wet methods of chemical analysis, (2) the dry methods of blowpipe analysis, in which the mineral is treated before the blowpipe without the use of liquid reagents except to a very subordinate degree, and (3) microchemical methods, per- formed on the stage of a compound microscope.
Blowpipe and microchemical analyses are made use of principally for the identification of minerals By their aid the nature of the atoms m a compound may easily be learned, but the proportions in which these atoms are combined is determined only with the greatest difficulty. The methods are mainly qualitative
Wet Analysis.— For exact determinations of composition the wet methods of chemistry are usually employed, since these are the most accurate ones They are identical with the methods described in manuals of quantitative analysis, and therefore require no detailed discussion here They are well illustrated by Prof Tschermak as follows. If 734 mg. of the mineral goethite (in which qualitative tests show the presence of iron oxide and water) are roasted in a glass tube, water is given off This when caught and condensed m a second tube containing dry calcium chloride increases the weight of this second tube by 75 mg The residue of the mineral left in the first tube now weighs about 660 mg An examination of this residue shows it to con- sist exclusively of the iron oxide (FejjOs) Since only iron oxide and water are present in goethite the sum of these two constituents ought to equal the original weight of the mineral before roasting But 660+75 — 73SJ whereas the original weight was 734 The difference i mg. is| due to unavoidable errors of manipulation. As it is very small it may" be neglected in our calculations
The results of the analysis are generally expressed in percentages.
Composition And Classification 5
which are obtained by dividing the weights of the different constituents by the weight of the original substance
Thus: 660- 734= 89 92 per cent Fe20s
75"~734= 10 22 per cent EfeO
Total 100 14
The usual methods of analysis are, however, more indirect than this, the components of the substance to be analyzed being first transformed into known compounds and then weighed For instance, common salt is known by qualitative tests to contain only Na and CL If 345 mg. of the pure salt be dissolved in water and the solution be treated with silver nitrate under proper conditions a precipitate of silver chloride is formed so long as any sodium chloride remains in the solution. The silver chloride is separated from the solution by filtration It contains all the chloride present m the 345 mg of salt After drying, its weight is determined to be 840 mg The solution from which the silver chloride was separated contains all the sodium that was originally present in the salt, but now it is in combination with nitric acid It contains also any excess of silver nitrate that was added to precipitate the chlorine
NaCl + AgNOs - AgCl + NaN03
salt reagent precipitate filtrate
The filtrate is now treated with hydrochloric acid to precipitate the excess silver The silver chloride precipitate is removed by filtra- tion, leaving a solution containing sodium salts of nitric and hydro- chloric acids besides some free acid of each kind. Sulphuric acid is now added and the whole solution is evaporated to dryness. The free acids are driven off by the heat and the sodium salts are transformed into the sulphate, Na2S04 The residue consisting exclusively of NaaSO* is now found to weigh 419 mg.
The 345 mg of salt have yielded 840 mg. of AgCl and 419 mg. of NagS04 The silver chloride is known to contain 24 74 per cent of chlorine and the sodium sulphate 32 39 per cent of sodium. The 840 mg of AgCl contain 207.8 mg of chlorine, and the 419 mg of contain 135 7 mg. of sodium. Hence 345 mg of salt yield
207.8 mg. or 60.23 per cent Cl, and 135 7 mg. or 3934 per cent Na
343.5 mg. 99.57 per cent
6 General Chemical Mineralogy
Records of Analyses. — The composition of minerals like that of other chemical compounds is determined in percentages of their com- ponents and is recorded as parts per 100 by weight. A weighed quantity of themmeral is analy/ed, the products of the analysis are weighed and the percentage of each constituent present is found by dividing its weight by the weight of the original substance, as has already been indicated
In chemical treatises the results of the analyses are usually recorded in percentages of the elements present. In mineralogical works it is more common to write the percentage composition in terms of the oxides of the elements, partly because the old analyses are recorded in this way and partly because certain relations between the mineral components can be better exhibited by comparison of the oxides than by comparison of the elements present in them.
The record of the analysis of a magnestte may be given as.
Mg=2835 per cent,
Fe= 34 per cent,
0=14 25 per cent,
0=5698 per cent,
Total =99,92 per cent
or as
MgO=47 25 per cent, FeO= 43 per cent, C02=S2 24 per cent,
Total =99 92 per cent.
Calculation of Formulas. — After the determination of the per- centage composition of a mineral, the next step is to represent this composition by a chemical formula — a symbol which indicates the relative number of elementary atoms in the mineral's molecule, instead of the number of parts of its constituents in 100 parts of its sub- stance.
The construction of a formula from the analytical results is simple enough in principle, but in practice it is often made difficult by the fact that many apparently pure substances are in reality composed of several distinct compounds so intimately mtercrystallized that it is impossible to separate them In the simplest cases the formula is derived directly from the results of the analyses by a mere process of division.
The atomic weights of the chemical elements are the relative weights of the smallest quantities that may enter into chemical combination with one another, measured in terms of the atomic weight of hydrogen which is taken as unity, or of oxygen taken as 16. Thus the atomic weights of nitrogen and oxygen are approximately 14 and 16 respectively, i.e., the smallest quantities of nitrogen and oxygen that can enter into com- bination with each other and with hydrogen are in the ratio of the
Composition And Classification
Table Of Atomic Weights
Element
Symbol
At Weight
Element Symbol
At. Weight
Aluminium
Al
Molybdenum
Mo
96 o
Antimony
Sb
Neodymium
Nd
Argon
A
Neon
Ne
Arsenic
As
Nickel
Ni
Barium
Ba
Niton
Nt
Bismuth
Bi
208 o
Nitrogen
N
14 oi
Boron
B
Osmium
Os
Bromine.
Br
Oxygen
16 o
Cadmium
Cd
Palladium
Pd
Caesium
Cs
Phosphorus
P
Calcium
Ca
Platinum
Pt
Carbon
12 Oos
Potassium
K
Cerium
Ce
Praseodymium
Pr
Chlorine
Radium
Rd
226 o
Chromium
Cr
Rhodium
Rh
Cobalt
Co
Rubidium
Rb
Columbium
Cb
Ruthenium
Ru
Copper.
Cu
Samanum
Sa
Dysprosium
Dy
Scandium .
Sc
Erbium
Er
Selenium
Se
Europium
Eu
152 o
Silicon
Si
Fluorine
F
19 o
Silver
Ag
Gadolinium
Gd
Sodium
Na
23 o
Gallium
Ga
Strontium
Sr
Germanium
Ge
Sulphur
S
Glucinum
Gl
Tantalum
Ta
Gold..
Au
Tellurium
Te
Helium
He
4 oo
Terbium
Tb
Holmmm.
Ho
Thallium
Tl
204 o
Hydrogen
H
Thorium
Th
Indium.
In
Thulium
Tm
Iodine. . .
Tin
Sn
Indium. .
Ir
Titanium
Ti
Iron
Fe
Tungsten
W
184 o
Krypton
Kr
Uranium
U
Lanthanum
La
139 o
Vanadium
Lead .
Pb
Xenon
Xe
Lithium
U
Ytterbium (Neoytterbium)
Yb
Lutecium..
Lu
Yttrium, .
Y
Magnesium. ..
Mg
Zinc .
Zn
Manganese. .
..Mn
,Zr
..,,Hg
200,6
8 General Chemical Mineralogy
values 14 1 6 : i l The quantities that possess these relative weights are known as atoms Often the apparent ratios ot the elements in combination are different from the uitios between their atomic weights, but this is always due to the fact that one or the other of the elements is present in more than its smallest possible quantity, i e , in a greater amount than is represented by a single atom For instance, there are several compounds of oxygen and nitrogen known, in which the weight relations between the two elements may be represented by the follow- ing figures 14 : 8, 14 : 16, 14 24, 14 : 32, and 14 : 40 If the second of these compounds consists of one atom each of nitrogen and oxygen, and these are the smallest quantities of the elements that can exist in combination, the several compounds must be made up thus
14 : 8 14 . 16 14 . 24 14 : 32 14 40
N2O No N203 N02 N205
for N can exist only in quantities that weigh 14, 28, 42 times as much as the smallest quantity of hydrogen present in any compound, i e , the single atom, and 0 in quantities of 16, 32, 48, etc , times the weight of the single hydrogen atom In order that even multiples of 14 and 1 6 shall exist in the ratios given above, their terms must be multi- plied by quantities that will yield the following results.
28 . 1 6 14 : 16 28 48 14 32 28 : 80
which are the weights respectively of the numbers of atoms lepresented in the above formulas
If, then, the elements combine in the ratio of their atomic weights, or in some multiple of this ratio, the figures obtained by analysis must be in one of these ratios, and consequently they furnish the data from which the formula of the substance analyzed may be deduced In gold chloride, for example, analysis shows the presence of 64 87 per cent Au and 35 13 per cent Cl, i e , the gold and the chlorine are united in
the ratio of 64.87 ; 35 13 or -i-I. The combining ratio of single
atoms of gold and of chlorine is, however, 196 7 35 5, or -2—Z £Vi-
oo 5 dently in gold chloride the ratio of gold to chlorine is only one-third
as great as is the ratio between the atomic weights of these elements, or the ratio of the chlorine to the gold three times as great. Hence
1 The atomic weight of hydrogen is more accurately i 008, when that of oxygen is taken as 16
Composition And Classification
there must be three times as much chlorine in gold chloride as would be represented by a single atom of chlorine, or there must be three atoms of chlorine in the compound, for we cannot imagine a quantity of gold present which is equivalent to one-third of an atom of gold Gold chloride is therefore AuCls
We can now prove our conclusion by calculation One atom of gold and three atoms of chlorine ought to combine in the ratio of 1967:1065 (le, 355X3) If our conclusion is correct, and the gold chloride analyzed is AuCls, then the quantities of gold and of chlorine yielded by the analysis should be in this ratio The figures obtained are in the ratio of 64 87 : 35 13 Multiplying both terms of this ratio by 3 031 we obtain 196 62 . 106 5, which is approximately the ratio expected.
In practice, the same result as that outlined above is reached by dividing the results of analyses by the atomic weights of the various elements or groups of elements concerned The quotients represent the proportional numbers of the elements or groups present. If the small- est quotient is assumed as unity, the ratios existing between this and the other quotients indicate the number of atoms or groups of atoms represented by the latter.
Illustrations,
Gold Chloride Result of Analysis Atomic Weights Quotients
Au 64 87 per cent — 196 7 3298 Cl 35 13 35 5 - 9896
Tin Chloride
Sn
45 26 per cent - 117 4 384 54 74 35 5 542
Ratios
The formula of the gold chloride is AuCls, and of the tin chloride, SnCU
Magnesium carbonate on analysis may yield: 14.26, Mg= 28 37; Fe=.34, 0=5703, or, if recorded m the form of oxides: 002=52.24, MgO=47 25, FeO= 43 From either of these results the formula is easily obtained by the method described.
C=i4 26—11 97=1 188=1 009,
Mg= 28 37- 23.94= i 186=1.000,
Fe~ .34-5588= .006= .006,
0=57.03-15 96=3 573=3-°i2,
or,
MgCOs, if we neglect the small quantity of iron present
10 General Chemical Mineralogy
From the second set of figures we have*
0)2=5224-4389=1 19 1, ] or>
MgO=47 25— 3990=1 184=1, r MgO C02, which is the same as FeO= 43—7184= 006, J MgCOs, written in a different way
All formulas are derived by methods like these, but in many cases the processes are made more difficult by the impossibility of deciding positively whether those substances that are present in small quantities are present as impurities or whether they exist as essential parts of the compound
Formulas of Substances Containing Two or More Metallic Elements or Acid Groups. — In the illustration given above the com- pounds consist of but one kind of metallic element combined with one kind of acid Often in the case of minerals there are present two or more metallic elements, and less commonly several acid groups. When two metals are present in definite atomic proportions the formula is written in the usual manner, as CaMg(COs)2 for the mineral dolomite, in which calcium and magnesium are present in the ratio of one atom of each to two parts of the acid group COa. Very often, and perhaps in the majority of cases, when two or more metallic elements are present in different specimens of a mineral they are not found always in the same proportion — the mineral may consist of isomorphic mixtures of several substances For instance, many calcium-magnesium car- bonates are known in which the ratio of calcium to magnesium present is not as i atom to i atom, but in which this ratio is as 2 atoms to i atom, 3 atoms to 2 atoms, or a ratio which would have to be represented by irrational figures like 2 7236 atoms to i 5973 atoms Each one of these compounds properly requires a separate formula, as aCaCOa+MgCOs, 3CaC03+2MgCO3, etc , but practically the entire series of compounds is represented by a single symbol, thus (Ca Mg) COs, indicating that in the series we have to do with mixtures of carbonates of calcium and magnesium, or with complex molecules containing in different instances different proportions of the two carbonates. For greater defimteness the symbol of the characteristic element of the substance which is in largest quantity in the compound is usually written first, as (Ca Mg)COs, when calcium carbonate is m excess, or (Mg Ca)COs when pnagnesmm carbonate predominates If still greater defimteness is desired small figures are placed below the symbols of the elements concerned, as (Ca2 Mgi)COs or (Ca3 Mg2)C03, to indicate the respective proportions present. (Ca2 Mgi)COs signifies that the
Composition And Classification 11
mineral thus represented contains calcium and magnesium in the ratio of 2 atoms of the former to i of the latter
Compounds Containing Water.— Often salts that separate from aqueous solutions combine with certain definite proportions of water Sometimes this water combines with the anhydrous portion of the com- pound to form a double salt, as MgSO4+7H20, or MgS04 7H20 At other times a portion of the water, in the form of the group (OH), called the hydroxyl group, occupies the place usually occupied by a metallic element, and, occasionally, that usually occupied an acid group, or by oxygen, as in Mg(OH)2
Water of Crystallization.— Double salts composed of an anhydrous portion combined with water are usually well crystallized Although the water appears in many cases to be but loosely combined with the remainder of the compound it is an essential part of its crystal particle, for by the loss of even a portion of it the crystal system of the compound is often changed Water in this form is known as water of crystalliza- tion, and the compounds are designated hydrates
The magnesium sulphate MgSO* 7HaO forms orthorhombic crystals By evaporation of a hot solution of this substance the sulphate MgSO4 6H20 separates as monochmc crystals.
Gypsum is CaSOi 2H2O Its crystallization is monoclinic When heated to 200° it passes into the anhydrous orthorhombic mineral anhydrite, CaS04
Water of crystallization may frequently be driven from the com- pound in which it exists by continued heating at a comparatively low temperature. It is usually given off gradually — an increase in the tem- perature causing an increase in the quantity of water released until finally the last trace disappears In many instances such a very high temperature is required to drive off the last traces of the water that it would appear that some of it is held m combination in a different manner from that in which the remainder is held Indeed, it is not at all certain that double salts containing water of crystallization are different in any essential respect from ordinary atomic molecules in which hydrogen and oxygen are present in atomic form.
Combined Water.— Water of crystallization is thought of as existing in the compound as water because of the ease with which it can be driven off Compounds in which the hydroxyl group is present yield water only upon being heated to comparatively high temperatures In them the elements of water are present, but not united as water. When freed from their combinations with the other constituents of the compound by heat they unite to form water Because its elements
12 General Chemical Mineralogy
are thought of as closely combined with the other elements in the molecule, this kind of water is often distinguished from water of crystal- lization by the term combined water.
Bructte (Mg(OH)2) and malachite (Cu2(OH)2C03) are minerals containing the elements of water When heated they yield water according to the reactions Mg(OH)2 MgO+H2O and Cu2(OH)2COs CuO+CuC03+H20.
Combined water is not only more difficult to separate from its com- bination than is water of crystallization, but when the combination is broken the chemical character of the original substance is radically changed, as may be seen from the reactions above indicated. More- over, combined water is given off suddenly, at a certain minimum temperature, and not gradually as in the case of water of crystal- lization.
Blowpipe Analysis. — Although blowpipe analysis serves merely to identify the chemical components of minerals, it is a most important aid to mineralogists in their practical work
Nearly all minerals may be recognized with a close degree of accu- racy by their morphological and physical properties To distinguish between several minerals that are nearly alike in these characteristics, however, the determination of composition is often important In" cases of this kind a single test made with the blowpipe will frequently give the desired information as to the nature of some one or more of the chemical elements present, and thus in a few moments the mmeial may be identified beyond mistake
The apparatus necessary to perform blowpipe analysis is very simple and the number of pieces few These, together with all the reagents in sufficient quantity to determine the composition of hundreds of minerals, may be packed into a box no larger than a common lunch box (See pp 467-470)
For more refined work than the mere testing of minerals a larger collection of both apparatus and reagents is necessary, but it no case is the quantity of material consumed in blowpipe analysis as great as when wet methods of analysis are used
Principles Underlying Blowpipe Analysis.— The principal phe- nomena that are the basis of blowpipe work are the simple ones known in chemistry as volatilization, reduction, oxidation, and solution
For volatilization experiments charcoal sticks and glass tubes are used A blowpipe serves to direct a hot blast upon the assay. The volatilized products collect on the cool parts of the charcoal which they coat with a characteristic color, or upon the cooler portions of
Composition And Classification 13
tlie glass tubes The sublimates that collect in the tubes may be tested with reagents or examined under the microscope
Some volatile substances impart a distinct and characteristic color to an otherwise colorless flame These may be tested in the direct flame of the blowpipe
Oxidation and reduction experiments are usually performed either on charcoal or in glass tubes Oxidations are effected in open tubes and reductions in those closed at one end The products of the oxida- tion or of the reduction are studied and from their characteristics the nature of the original substance is inferred
The solution of bodies to be tested is often made in the usual man- ner, i.e , by treatmg them with liquid reagents, but more frequently it is accomplished by fusion of a small quantity of the body with borax (Na2B407 ioH20) or microcosmic salt ((NH4)NaHPO4 4H2Q). The molten reagent dissolves a portion of the substance to be tested and in many cases forms with it a colored mass From the color of the mass the nature of the coloring matter may be learned.
Although the underlying principles of blowpipe analysis are simple the reactions that take place between the reagents and the assay are often very complex.
More explicit details of the operations of qualitative blowpipe analysis are given in Part III
Microchemical Analysis. — The processes of microchemical analysis are limited in their application to the detection of a single element or, at most, of a very few elements in small quantities of minerals. They are employed mainly in deciding upon the composition of a substance whose nature is suspected
The principle at the basis of all microchemical methods is the manu- facture of crystallized precipitates by treatment of the mineral under investigation with some reagent, and the identification of these pre- cipitates through their optical and morphological properties.
In practice, a small particle of the mineral the nature of which it is desired to know is placed on a small glass plate, which may be covered with a thin film of Canada balsam to prevent corrosion, and is moistened with a drop or two of some reagent that will decompose it The solution thus formed is slowly evaporated by exposure to the air The plate is then placed beneath the objective of a microscope and the crystals formed during the evaporation are investigated Or, after a solution of the assay is obtained there is added a small quantity of some reagent and the resulting precipitate is studied under the microscope. By their shapes and optical properties the nature of the
14 General Chemical Mineralogy
FIG i — Sodium Fluosilicate Crystals Magnified 72 diam (After Rosenbusch )
FIG 2 —Potassium Fluosihcate Crystals Magnified 140 diam, (After Rosenbusch )
Composition And Classification 15
crystals produced is determined, and in this way the nature of the con- stituents they have obtained from the mineral particles is discovered
A large number of reagents ha\ e been used m microchemical tests each of which is best suited to some particular condition The most generally useful one is hydrofluosihcic acid (H2SiFb). If small frag- ments of albite and of orthoclase are placed on separate glass slips, such as are used for mounting microscopic objects, and each is treated with a drop of this reagent and then allowed to remain in contact with the air lor a few minutes until the solutions begin to evaporate, those portions of the solutions remaining will be discovered to be filled with little crystals The crystals in the solution surrounding the albite are hexagonal m habit (Fig i), while those in the solution surrounding the orthoclase are cubes, octahedrons or combinations of forms belonging to the isometric system (Fig 2). The former are crystals of sodium fluosihcate and the latter crystals of the corresponding potassium salt The albite, consequently, is a sodium compound and the orthoclase a compound of potassium In similar manner, by means of this or of other reagents the constituents of many minerals may be easily detected The method, however, is made use of only in special cases, when for some reason or other analytical methods are not applicable
Synthesis. — Synthesis is the opposite of analysis. By the analytical processes compounds are torn apart, or broken down, whereas by syn- thetical operations they are put together or built up Synthetic methods are employed principally in the study of the constitution of minerals and of their mode of formation, and in the investigation of the condi- tions that determine the different crystal habits of the same mineral The products of synthetic reactions are often spoken of as artificial minerals because made through man's agency In many instances these artificial minerals are identical in every sense with natural minerals Consequently, they may often serve as material for study, when the quantity of the natural mineral obtainable is too small for the purpose
Classification of Minerals. — Classification is the grouping of objects or phenomena in such a manner as will bring together those that a're related or that are similar in many respects and will separate those that are different
Since minerals are chemical compounds whose properties depend upon their compositions, then* most logical classification must be based upon chemical relationships. But their morphological and physical properties are their most noticeable features, and hence these should also be taken into account in any classification that may be adopted. Probably the most satisfactory method of classifying minerals is to group them,
16 General Chemical Mineralogy
first, in accordance with their chemical relationships and, second, m accordance their morphological and physical properties
The first division is into the great chemical groups, as, for instance, the elements, the chlorides, the sulphides, etc The second division is the separation of these great groups into smaller ones comprising minerals possessing the same general morphological features These smaller groups may contain only a single mineral or they may contain a large number of closely allied ones If the basis of the subgroupmg is manner of crystallization, it follows that the members of subgroups containing more than one member are usually isomorphous compounds Thus the subdivisions of the great chemical groups are single minerals and small or large isomorphous groups of minerals, arranged in the order in which their metallic elements are usually discussed in treatises on chemistry For example, the great group of carbonates embraces all minerals that are salts of carbonic acid (EfeCO'j) This great group is divided into smaller groups along chemical lines, as for instance, the normal carbonates, the hydrous carbonates, the basic carbonates, etc These smaller groups are finally divided into subgroups according to their morphological properties — the normal salts, for example, being divided into the two isomorphous groups known as the calcite and the aragonite groups, and a third group comprising but a single mineral
In certain specific cases some other classification than the one outlined above may be desirable For instance, in books written for mining students it is often found that a classification based upon the nature of the metallic constituent is of more interest than the more strictly scientific one outlined above, because such a classification emphasizes those components of the minerals with which the mining student is most concerned In books written for the student of rocks, on the other hand, the most important determinative features of minerals are their morphological characters, hence m these the classification may be based primarily on manner of crystallization
In the present volume the classification first outlined is used, but because such a small proportion of the known minerals are discussed the beauties of the classification are not as apparent as they would be were ail described
Chapter Ii The Formation Of Minerals Axd Their Alterations
The Origin of Minerals.— Minerals, like other terrestrial chemical compounds, are the result of reactions between chemical substances existing upon the earth When they are the direct result of the action of elements or compounds not already existing as minerals they are said to be primary products, when formed by the action of chemical agents upon minerals already existing they are often spoken of as secondary, though this distinction of terms is not always applied
Quartz (SiCb), formed by the cooling of a molten magma, is pnmar> , when formed by the action of water upon the siliceous constituents of rocks it is secondary
The Formation of Primary Minerals — Minerals are produced in a great variety of ways under a great variety of conditions Even the same mineral may be produced by many different methods The more common methods by which primary minerals are formed are precipita- tion from a gas or a mixture of gases, precipitation from solution, the cooling of a molten magma, and abstraction from water or air by plants and animals
Deposits from Gases. — Emanations of gases are common in vol- canic districts The gases escaping from volcanic vents are mainly water vapor, hydrochloric acid, sulphur dioxide, sulphuretted hydro- gen, ammonia salts and carbon dioxide, besides small quantities of other gases and the vapors of various metallic compounds By the reactions of these with one another or with the oxygen of the air, sulphur, salam- momac (NHiCl) and other substances may be formed, and by their reaction upon the rocks in the neighborhood halite (NaCl), ferric chlo- ride (FeCls), hematite (Fe20s) and many other compounds may be produced
The production of minerals through the reactions set up between various gases and vapors is known as pneumatolysis Their separation from the gaseous condition is known as sublimation Minerals formed by sublimation are usually deposited as small, brilliant crystals on the surfaces of rocks or upon the walls of cavities and crevices in them.
18 General Chemical Mineralogy
The reactions by %\hich they are produced are often quite simple. Thus the reaction between sulphuretted hydrogen and sulphur dioxide yields sulphur (2H2S+S02 3S+2H20), as does also the reaction between the first named gas and the oxygen of the atmosphere (HjS+O H2O+S) Ferric chloride may be produced by the action of hot hydrochloric acid upon some iron-bearing material deep within the earth's in- terior This being volatile at high temperatures escapes to the air as a gas Here it may react with water vapor, with the resulting for- mation of hematite (2FeCl3+3H20=Fe203+6HCl) By the action of carbonic acid gas upon volatile oxides, carbonates are formed, (Fe203+2C02=2FeCOa+0) In other cases, however, the reactions are very complicated
Precipitation from Solution. — Nearly all substances are soluble to an appreciable degree in pure water An increase in temperature usually increases the quantity of the substance that can be dissolved, as does also an increase of pressure Moreover, the solubility of a salt is increased on the addition of another salt containing no common ion, and, conversely, is diminished in the presence of another having a common ion Thus, gypsum (CaS04 2H20) is sparingly soluble in water, but it becomes much more soluble upon the addition of salt (NaCl) On the other hand, salt (NaCl) is much less soluble in water containing a little magnesium chloride (MgClo) than it is in pure water.
When a solvent contains a maximum amount of any substance that it may hold under a given set of conditions the solution is said to be saturated From a saturated solution under ordinary conditions precipitation results Upon the evaporation of the solvent, the lowering of its temperature or of the pressure under which it exists, or the addi- tion to the solution of a substance containing an ion already in the solution. Of course, the addition of a substance which will react with the solution and produce a compound insoluble m it will also cause precipitation
The following table contains the results of various experiments on the solubility of some common minerals
SOLUBILITY OF VARIOUS COMPOUNDS IN 100 PARTS PURK WATFR (The results are given in parts by weight)
Halite (NaCl), at 7° 35 68 Calcitc (CaCO,), in the Fluonte (CaF2), at 15° 0037 cold 002
Gypsum (CaS04 2H20),ati5° 250 Strontiamte (SrCO,) in Anhydrite (CaS04), in the cold 00025 the cold 00555
Celestite (SrS04), at 14° 015 Magnetite (Fte()4) 00035
Formation Of Minerals 19
Percentages Of Various Minerals Soluble In Water 80°
(When treated 30 to 32 da\s)
Galena (PbS) 179 Chalcop>nte CCuFeS2) 1669
Stibmte (Sb2S3) 5 01 Bouraomte f(Pb Cu)SbS3) 2 075
Pynte (FeS2) 2 99 Arsenopynte (FeAsSj i 5
Sphalerite (ZnS) 025
So many substances that are usually regarded as insoluble are known to be dissoh ed under conditions of high temperature and pressure that no substance is behe\ ed to be entirely insoluble
Po\\dered apophylhte ((HK)2Ca(Si03)2 H20), which is a silicate that is generally regarded as insoluble in water, is dissoh ed sufficiently in this sohent at a temperature of i8o°-iQO° and under a pressure of 10-12 atmospheres to }ield crystals of the same substance upon cooling
Water containing gases or traces of salts is usually a more efficient dissolving agent than pure water When the gases are lost, or the salts are decomposed by reactions with other compounds, precipitation may ensue
PARTS OF VARIOUS MINERALS DISSOLVED ix 10,000 PARTS OF VARIOUS
Solutions
Gold loses i 23 per cent of its \\eight when treated with 10 per cent soda solution at 200°
One part gypsum (CaSO4 2H20) dissolves in 199 parts of saturated NaCl solution Only 4 part dissolves in 200 parts pure \\ater
Pyt lie (FeSo) loses 10 6 per cent of its mass upon boiling for a long time with a solution of Na2S Under the same circumstances galena loses 2 3 per cent
One of the commonest of the gases found in water on the earth's surface is carbon dioxide This is an active agent in decomposing sili- cates and in dissolving carbonates, so that water m which it is dissolved is usually a more powerful solvent than pure water Its dissolving power increases with the pressure, as in the case of pure water, but diminishes with increasing temperature The action of carbonated water on silicates is due to the replacement of the silicic acid by carbonic acid and the production of bicarbonates, which are usually more soluble than the corresponding carbonates The greater solubility of carbon- ates, like calcite, in carbonated water is also due to the formation of bicarbonates For example, the action of carbonated water upon cal- cite (CaCOs) is as follows
CaC03+H20+C02=CaIfc(C03)2.
20 General Chemical Mineralogy
Carbonated water is more effective as a solvent under pressure because of the inability of the CCb to escape under this condition When pressure is removed the CCb escapes, or evaporation takes place, and the reverse reaction occurs, as
CaH2(C03)2= CaC03+H20+CO2
The dissolving effect of carbonated water upon various carbonates and other minerals and the influence of pressure and temperature upon the solution of a carbonate are indicated in the three tables following
Solubility Op Certain Carbonates In 10,000 Parts Of Carbonated
Water
(The results are given in parts by weight)
Calcite (CaC03), at 10° 10 o Sidente (FcCO,) at 18° 7 2
Dolomite (CaMg(COs)2) at 18° 3 i Witherite (BaCOj) at 10° 170
Magnesite (MgCOs), at 5° 13 i Strontiamte (SrCOi), at 10° 12 o
Percentages Of \Arious Minerals Soluble In Carbonatfd Watlr
(When treated 7 weeks)
Adulana (KAlSiaOs) 328 Apatite (Ca(F CIXPCX).) i 821
Ohgoclase Apatite (Cafi(F Cl)(POi)0 2 018
(NaAlSi308+ CaAl(SiO)4) 533 Olivme ((Mg Fe)2Si04) 2111
Hornblende (complex silicate) i 536 Magnetite (Fe304) 307 to i 821 Serpent] ne (KUMgsSi'Oo) i 211
INFLUENCE OF TEMPERATURE AND PRESSURE UPON THE SOLUTION OF MAGNESIUM CARBONATE (MgC03) IN CARBONATED WATER
(The results are given m parts per 10,000 by weight)
i atmos at 19° 2 579 parts Temp 13 4° under i atmos 2 845 parts 32 3 730 29 3 2 105
56 4 620 62 o i 035
75 5 120 82 o 400
90 5 659 100 o ooo
Precipitation from Atmospheric Water —Rain is an active agent in dissolving mineral matter Since it absorbs small quantities of carbon dioxide, sulphur gases and other substances as it passes through the atmosphere it may act upon many compounds, dissolving some, decom- posing others and forming soluble compounds from those that would otherwise be practically insoluble Moreover, it transports the dissolved materials from one portion of the crust to some other portion, where, under favorable conditions, they may be precipitated The rain water that penetrates the earth's crust, dissolving and precipitating in its
Formation Of Minerals
course through the crust, is known as vadose water It is an important agent in ore-formation, since it may collect mineral matter from a great mass of rocks and precipitate it in some favorable place, thus making ore bodies
Deposits of Springs. — Springs are the openings at which under- ground \\ater escapes to the earth's surface Much of the water flowing from springs is the meteoric water which has circulated through the crust and is again seeking the surface In its course through the crust it dissolves certain materials Where it reaches the surface some of this material may be dropped in consequence of (i) evaporation of the \\ater, or (2) the escape of carbon dioxide, or (3) the oxidation of some of its constituents through the action of the air, or (4) the cooling of the water in the case of warm or hot springs
The deposits thus formed may occur as thin coatings on the rocks over which the spring water passes, or as layers in the bottom of the spring and the stream issuing from it Among the commonest minerals thus deposited are calcite (CaCOs), aragomte (CaCOs), siderite (FeCOs) and other carbonates, gypsum (CaSO-i 2H20), pynte (FeS2), sulphur (S), and limonite (Fe4O3(OH)6) The carbonates are deposited largely in consequence of the escape of C02 from the water, gypsum in conse- quence of cooling, and limonite and sulphur through oxidation. If the water contains EkS, this reacts with the oxygen and a deposit 4 j, of sulphur ensues (compare P 18)
When the precipitation oc- curs m cracks or fissures in the rocks the precipitated matter may partially or completely fill the fissure, producing a vein, or, the precipitated matter may fill an irregular cavern forming a bonanza It sometimes covers the walls of cavities or the sur- faces of minerals already exist- ing, giving rise to a druse In other cases precipitation may occur while the solution is dripping from an overhanging surface, making a stalactite, or the precipitate may fill the tiny crevices between grains of sand cementing the loose mass into a compact rock
Mmerals produced by precipitation are often beautifully crystallized.
FIG 3 — Cross-section of Symmetrical Vein (Aflts Le Neue Foster )
(a) Decomposed rock ($) Galena
(6) Quartz crystals (d) Sidente
22 General Chemical Mineralogy
At other times they form groups of needles yielding globular and other imitative shapes, while in still other instances they occur as pulverulent or amorphous masses The fillings of veins are often arranged sym- metrically, similar materials occurring on opposite sides of their central planes in bands, as shown in the figure (Fig 3) Some important ores have been concentrated and deposited in this way
Deposits from Hot Springs.-— The water of hot springs deposits a greater variety of minerals than that of cold springs Practically all minerals that are soluble in hot water or in hot solutions of salts are among them Among those of economic value may be mentioned cinnabar (HgS) and stibnite (Sb2Ss)
Deposits from the Ocean and Lakes. — The water of the ocean and of many lakes is rich in dissolved salts. That of lakes, however, is often saturated or nearly so, while that of the ocean is not near the saturation point. Consequently, while many lakes may deposit mineral sub- stances, the ocean does not do so except under peculiar conditions When a portion of the ocean is separated from the mam body of water, it may evaporate and leave all of its mineral matter behind Lakes may also completely evaporate with a similar result In each case the deposits form layers or beds at the bottom of the basin in which the water was collected.
In other instances the water brought to the ocean or a lake may contain substances which will react with some of the materials already present and produce an insoluble compound which will be precipi- tated
Of course, the nature of the beds thus formed will depend upon the character and proportions of the substances that were in the water The ocean will yield practically the same kinds of compounds all over the world and the beds deposited by the evaporation of ocean water will be formed in nearly the same succession everywhere In the case of enclosed bodies of water — like lakes or seas — in which the composi- tion of the water may differ, the deposits formed may also differ
Many of the deposits formed in bodies of water are of great eco- nomic importance and, consequently, are extensively worked Prob- ably the most important are the beds of salt (NaCl) and of gypsum (CaSO4 2H20), although borax (Na2B407 ioH20) was foimerly obtained in large quantity from the deposits of some of the lakes in the desert portions of the United States
In the following table are given the results of analyses of water of the ocean and of Great Salt Lake, in Utah, calculated on the assump- tion that the elements are combined in the manner indicated m the
Formation Of Minerals
column on the left The results of the analyses of the waters of a few noted lakes are given in the succeeding table
Composition Of Saxts Contained In Water Of The Ocea.N And Gre\T
NaCl
Kci
MgCL
CaS04
MgS04
Na2S04
LAKE (Parts in 1000 of Water)
27 3726 8 1163
5921 1339
3 3625 6115
1 3229 9004
2 2437 3 0855
RbCl2
MgBr2
Ca3(P04)2
CaC03
FeC03
Si02
Ooii
in
tr
I Water of N Atlantic off Norwegian Coast Anal>st, C Schmidt II Average of Five Analyses, Caspian Sea at depths of from i m to 640 m
Analyst, C Schmidt III Great Salt Lake, Utah Analyst, O D Alien
PERCENTAGE COMPOSITION or THE RESIDUES OF A LAKE WATERS
Br
S04
Na
K
Ca
Mg
Si02
etc
Total Solids (per 1000 of Water)
Dead Sea Lake Beisk, Siberia Qoodenough Lake, B C Borax Lake, Cal
tr
7 Os
tr
Deposits from Magmatic Water. — Equally important in depositing mineral matter is the water that escapes from cooling lavas and other molten magmas — designated as juvenile water All molten magmas existing under pressure, i e , at some distance beneath the crust, contain the components of water, which escape as the magma cools or when the pressure diminishes, whether the diminution of the pressure is due to
24 General Chemical Mineralogy
the escape of the lava to the surface or to the cracking of the crust In its passage to the surface the hot water carrying dissolved salts pene- trates all the cracks and cavities in the rocks through which it passes in its ascent and deposits its burden of material, forming veins and other types of deposits Or, its components may decompose the materials with which it comes in contact, replacing them wholly or in part by the substances which it is carrying or by the products of decomposition
FIG. 4 —Cross-section of Vein in Green Porphyry The vein filling is chalcedonj The white splotches are feldspar crystals The fairly uniform character of the rock where not affected by the vein is seen on the right side of the picture The rude banding parallel to the vein is due to changes that have proceeded out- ward from the vein-mass into the rock
Since in many cases magmatic water contains corrosive gases, such as fluorine, its action on the rocks which it traverses is profound A tiny crack in the rocks may be gradually widened and the material on both sides of it be replaced by new material, thus producing a vein which is sometimes difficult to distinguish from a vein made in other ways (Fig 4) This process is known as metasomatism, which is one kind of metamorphism It is an important means of producing pseudomorphs and bodies of mineral matter sufficiently rich in metallic contents to constitute ore-bodies
Formation Of Minerals 25
Solidification from Molten Magmas.— A molten magma, such as a liquid lava, is probably a solution of various substances— mainly sili- cates— in one another, or in a hot solvent Upon cooling or upon change of conditions, such as may arise from loss of gas or water or from reduc- tion of pressure, this hot solution graduall} deposits some of its con- stituents as definite chemical compounds Upon further cooling other compounds solidify and so on, until finally, if the rate of cooling has been slo\\, the entire mass may separate as an aggregate of minerals— such as constitute many of the rocks, as granite for instance, and main of the lavas If the cooling has been rapid, some of the material ma\ separate as definite minerals \\hile the remainder solidifies as a homogeneous glass, as in the case of most lavas Sometimes the minerals thus formed are bounded by crystal planes, but usually their growth has been so interfered with that it is only by their optical properties that they can be recognized as crystalline substances The nature of the minerals that separate depends upon a great variety of conditions, the most important of which is the chemical composition of the magma
In some cases the minerals separating from a magma tend to segre- gate m some limited portion of its mass and thus produce an accumula- tion that may be of economic value, le, the magma dijf a entities Magnetite (FesGO, ilmenite ((Fe Ti)203), pynte (FeS2) and a few other minerals are sometimes segregated in this way in very large masses
Metamorphic Minerals — Many minerals are characteristic of rocks that are in contact with others that were once molten They were formed by the gases and hot waters given off from the magmas before they cooled The hot solutions with their charges of gas and salts penetrated the pores of the surrounding rock and deposited in them some of their material They reacted with some of the rock's components, producing new compounds, and extracted others, leaving pores into which new supplies of gas and water might enter In some cases the entire body of the surrounding rock has been replaced by new material for some distance from the contact Beyond this belt of most profound meta- morphism are other belts in which the rock is less altered, until finally in the outer belt is the unchanged original rock Into the outer contact belt perhaps only gas penetrated and the changes here may be entirely pneumatolytic Near the contact the changes may be metasomatic Minerals formed by these processes near the contact of igneous masses are frequently referred to collectively as contact minerals.
In other cases new minerals may be produced in rocks in consequence of crushing attended by heat Hot water under high pressure greatly facilitates chemical changes A part of the materials of the
26 General Chemical Mineralogy
crushed rock dissolves, reactions are set up and new compounds may be formed The new minerals produced are more stable than the original ones and have in general a greater density and consequently a smaller volume The type of metamorphism that produces these effects is kno\\n as dynamic metamot phism
Organic Secretions.— The transfer of mineral substances from a state of solution to the solid condition is often produced through the aid of organisms Mollusca, like the oyster, clam, etc , crustaceans, like the lobster or crab, the microscopic animals and plants known as pro-
FIG 5 — Diorite Dike Cutting Granite Gneiss Pelican Tunnel, Georgetown, Colo. (After Sptirr and Garry )
tozoans and algae and many other animals and vegetables abstract mineral matter from the water in which they live and build up for them- selves hard parts These hard parts, usually in the form of external shells, are composed of calcium carbonate (CaCOs), either as calcite or aragomte, of silica (8102) or of calcium phosphate Cas(P04)2. Although not commonly regarded as minerals these substances are identical with corresponding substances produced by inorganic agencies l
Paragenesis.— It is evident that minerals produced in the same
1 Plants and animals upon decaying yield organic acids which may attack minerals already existing and thus give nse to solutions which may deposit pynte (FeSa), hmomte (a hydrated iron oxide) or some other metallic compound This process, however, is properly simply a phase of deposition from solutions
Formation Of Minerals 27
ill generally be found together. A certain association of minerals will thus characterize deposits from magmas, another association
FIG 6 — Vein in Griffith Mine, Georgetown Colo , Showing Two Periods of Vein Deposition (After and Garry )
gn wall rock 6 sphalerite c — chalcopynte
ff comb quartz p pynte g galena
Balanceof vein-filling is a mixture of manganese-iron carbonates
13 Sh-
FIG 7 Vein Forming Original Ore-Body, Butte, Mont (After W.H Weed)
(i) Fault breccia, (2) ore, (3) altered granite, (4) first-class ore, (5) crushed quartz and
bormte, (6) fault clay, (7) solid pyrite and bormte, (8) crushed quartz and pynte, (9) solid
enargite ore with bormte, (10) banded white quartz and bormte, (n) white quartz, 6 inches,
(12) solid bormte, (13) solid pynte with bormte and quartz blotches, (14) bormte, (15) granite.
those precipitated from water, another those produced by contact action, etc This association of minerals of a similar origin is known
General Chemical Mineralogy
as their paragenesis From a study of their relations to one another the order of their deposition may usually be determined
Occurrence. — The manner of occurrence of mineral substance is extremely varied, as may be judged from the consideration of the vari- ous ways in which they are formed Deposits laid down in water occur in beds or in the cement uniting grains of sand, etc , such as the beds of salt (NaCl) or gypsum (CaSO* 2H20) found in many regions Those produced by the cooling of magmas may form great masses of rock such as granite, \which when it occurs as the filling of cracks in other rocks is said to have the form of a dike (Fig 5) Deposits made by
water, whether meteoric or mag- matic may give rise to veins, which may be straight-walled or branch- ing, like the veins of quartz (Si02) that are so frequently seen cutting various siliceous rocks When the veins aie filled by meteoric water they often have a comb-structure — the filling consisting of several sub stances arranged in definite layers following the vein walls (see p 21) If the composition of the depositing solution, whether meteoric or mag- matic, has remained constant for a long time the vein may be filled with a single substance It its com- position changed during the time the filling was in progress the layers are of different kinds Further, it deposition continued uninterruptedly the layers may match on opposite sides of the vein and the succession may be the same from walls to center If, however, after the partial or complete filling of the crack it was reopened and the new crack was filled, the new vein when filled would be unsymmetncal if the new crack occurred to one side of the center of the original vein (Fig 6) Repeated reopening may give rise to a vein that is so lacking in symmetry that it is difficult to trace the succession of events by which it was produced (Fig 7) Veins filled by magmatic water are frequently more homo- geneous.
Druses (Fig 8) arise when deposits simply coat the walls of fissures.
FIG 8 —Druse of Smithsomte (ZnCO3) on Massive Smithsomte
Formation Of Minerals
In many cases they may be regarded as veins, the development of which has been arrested and never completed When the deposits coat the walls of hollows within rocks they are known as geodes (Fig 9) Geodes are common in limestones and other easily soluble rocks in \*hich cavities may be dissolved
Gases and water under great pressure may penetrate the micro- scopic pores existing in all rocks and there deposit material which may fill the pores and cement the rocks If the deposited material is metallic the rocks may be transformed into masses sufficiently rich in metallic matter to become ore-bodies A body of this kind is known as an impregnation It is well represented by some of the low grade gold ores, such as those in the Black Hills
When rocks are decomposed bv the weather they are broken up
FIG 9 —Geodes Containing Calcite (CaCOs) Crystals
The rains wash the disintegrated substance into streams In its course downward to lakes or the ocean, the heavier fragments, such as metallic particles, may settle while the lighter portions are carried along Thus the heavy parts may accumulate in the stream bottoms These materials, consisting of gold, magnetite, garnet, pyrite and other min- erals of high specific gravity, form a loose deposit m the stream bed which is known as a placer. Gold is often found in placer deposits The lighter portions may be carried to the lake or sea into which the streams enter and may accumulate as sand on beaches and on the bottom near the shores as gravel, sand, silt, etc Most sand consists principally of quartz, but many sands contain also grains of feldspar and other silicates, and sometimes other compounds
30 General Chemical Mineralogy
Alteration of Minerals.— Minerals, like living things, are constantly subject to change Circulating waters may dissolve them in part, or completely, and transport their material to a distant place, there depositing it either in the form it originally possessed or in some new form On the other hand, the mineral substance may be decomposed into several compounds some of which may be carried off, while others are left behind Again, the material remaining behind may com- bine with other matter held in the water causing the decomposition, and may form with it a new mineral or a number of different minerals occupying the place of the original one This is m part metasomatism
The atmosphere may also act as a decomposer of minerals Through the agency of its oxygen it may cause their oxidation, or it may cause them to break up into several oxidized compounds Through the agency of its moisture, it may dissolve some of these secondary substances or it may form with them hydrated compounds The substances thus formed may be dissolved in water and carried off, or they may remain to mark the place of the mineral from which they were derived
Water, containing traces of salts, or gases in solution are exceedingly active agents in effecting changes in minerals Many examples of the alteration of practically insoluble minerals under the influence of dilute solutions are known Calcite (CaCOs), for instance, when acted upon by a solution of magnesium chloride (MgCb) takes up magnesium and loses some ©f its calcium Monticelhte (CaMgSi04) when acted upon by solutions of alkaline carbonates breaks up into a magnesium silicate and calcium carbonate. Dilute solutions of various salts are constantly circulating through the earth's crust and are there effecting trans- formations in the minerals with which they come in contact On, or near, the surface the transformations are taking place more rapidly than elsewhere because here the solutions are aided in their decompos- ing action by the gases of the atmosphere
The effect of the air in causing alteration is seen in the green coat- ing of malachite ((CuOHCOs) that covers surfaces of copper or of copper compounds exposed to its action In this particular case the coating is due to the action of the carbon dioxide and the moisture of the atmosphere. Other substances in contact with the air are coated with their own oxides, sulphides, etc.
Pseudomorphs —When the alteration of a mineral has proceeded in such a manner that the new products formed have replaced it particle by particle a pseudomorph results Sometimes the newly formed sub- stance crystallizes as a single homogeneous gram filling the entire space occupied by the original substance Usually, however, the alter-
Formation Op Minerals
ation begins along the surfaces of cracks or fissures in the body under- going alteration, or upon its exterior, thus producing the new material at several places contemporaneously (Fig 10) When the replace- ment takes place m this manner the resulting mass is a network of fibers of the new substance or an aggregate of grains with the outward form of the replaced mineral
With respect to their method of formation chemical pseudomorphs may be classified as alteration pseudomorphs and replacement pseudomorphs
Alteration Pseudomorphs. — Pseudomorphs of this class may be defined as those which retain some or all of the constituents of the original minerals from which they were derived.
Paramorphs. — Pseudomorphs composed of the material of the pseudomorphed substance with- out addition or subtraction of any component are known as paramorphs.
Paramorphism is possible only in the case of dimorphous bodies. It results from the rearrangement into new bodies of the particles of which the original body was com- posed.
Illustrations Calcite (hexagonal CaCOs) after aragomte (ortho- rhombic CaCOs), orthorhombic sulphur after the monoclinic variety.
Partial Pseudomorphs. — The great majority of pseudomorphs retain a portion, but not all, of the material of the original mineral They may be formed by the addition of material to the original body, by the loss of material from it, or by the replacement of a portion of its material by new material
Pseudomorphs formed by the addition of substance to that already existing are rare The substances most frequently added in the pro- duction of such pseudomorphs are oxygen, sulphur, the hydroxyl group (OH) and the carbonic acid group (CDs and COs)
Illustrations Malachite ((CuOHCOs) after copper, aoid argentite (Ag2S) after sher.
Pseudomorphs resulting from the loss of material are not common.
FIG 10 — Alteration of Ohvine into Ser- pentine The alteration is proceeding from the surface of the crystal and from surfaces of cracks that tra\erse it The black specks and streaks represent magnetite formed during the process (After Tschermak )
32 General Chemical Mineralogy
They are caused by the abstraction of one or more of the constituents of a compound
Illustration Native copper after cupnte (Cu20)
The greater number of partial pseudomorphs are formed by the sub- stitution of some of the components of the original mineral by a new material
Illustrations Limonite (Fe403(OH)6) pseudomorphs after sidente (FeCOs) may be formed by the following reaction
4FeC03+ 20+3H20 4C02+Fe403(OH) 6 Cerussite (PbCOs) may be formed from galena (PbS), thus PbS+40+Na2C03 PbC03+Na2S04
Replacement Pseudomorphs. — Often the entire substance of a mineral is replaced by new material, so that no trace of its original matter remains In this case the nature of the pseudomorphed min- eral can be discovered only from the form of the pseudomorph
Illustrations Quartz (Si02) after calcite (CaCOa) and gypsum (CaSO4 2H20) after halite (NaCl)
Mechanical Pseudomorphs. — The processes described above as originating pseudomorphs are chemical, and the resulting pseudomorphs are sometimes designated chemical pseudomorphs There is another class of pseudomorphs, however, in which the substance of a crystal has not been replaced gradually by the pseudomorphing substance In this class the pseudomorphing substance simply fills a mold left by the solution of some preexisting crystal Thus, if a sulphur crystal should become encrusted with a coating of bante (BaS04) and the temperature should rise until the sulphur melts and escapes, there would be left a mold of itself constructed of bante If, now, a solution of calcium carbonate should penetrate the cavity and fill it with a deposit of calcite (CaCOs), the mass of calcite would have the shape of a crystal of sulphur. Pseudomorphs of this kind are known as mechanical pseudomorphs
Weathering.—The term weathering is applied to the sum of all the changes produced in minerals by the action of the atmosphere upon them Although nearly all minerals show some traces of weathering, these traces may often be detected only by the slight differences m color exhibited by surfaces that have been exposed for a long time to the action of the air when compared with fresh surfaces produced by frac- ture or cleavage,
Formation Of Minerals 33
The weathering of minerals is often of great economic importance Veins of sulphides and a few other compounds may be oxidized where they outcrop on the surface Some of the decomposition products thu? formed may be soluble and others insoluble The insoluble products may remain near the surface while the soluble ones are carried down- ward by ground water along the course of the vein Here a reaction may ensue between the soluble salts and the undecomposed portion of the vein with the result that metallic compounds may be precipitated, thus enriching the original vein matter and causing it to be changed from a comparatively lean ore to one of great richness
Pynte veins on the surface are often marked by accumulations of hmonite derived by the oxidation of the sulphide With this may be mixed insoluble carbonates, silicates and other salts of valuable metals present in the original sulphide Weathering may extend downward along the veins for a short distance, replacing their upper portions with the oxidized decomposition products This portion of a vein is often spoken of as the o wdized zone, and this is sometimes the richest portion of the vein It may be rich because less valuable substances have formed soluble salts and have been drained away
Below the oxidized zone may be another zone less rich in valuable compounds than the oxidized zone, but much richer than the material below it The soluble decomposition products of the upper portion of the vein may percolate downward, and react with the unchanged vein matter, precipitating valuable metallic salts Although the original vein matter may contain an inconsiderable quantity of the valuable material, the precipitation in it of additional stores of material of the same kind may raise the percentage of this constituent to a point where it is profitable to mine it This belt of enriched ore is known as the zone of secondary em ichment
The oxidized zone extends downward from the surface to a depth at which the atmosphere and meteoric water become exhausted of their oxygen — a depth which varies with local conditions The zone of secondary enrichment extends from the bottom of the oxidized zone to a short distance below the level of the ground water, beyond which solutions will diffuse and thus be carried away from the vein. Below the zone of enrichment the original vein-filling may reach downward indefinite distances
Since many veins exhibit the features described, it follows that the ore of many mines must grow poorer with depth, and that in many instances the richest ore is near the surface
Some of the changes involved in weathering and secondary enrich-
34 General Chemical Mineralogy
ment of sulphide veins in limestone are indicated by the following reac- tions in the case of a vein containing pyrite (FeS2), sphalerite (ZnS), and galena (PbS)
(1) The first change produced at the surface may be the oxidation of the sulphides to sulphates
(a) ZnS+40=ZnS04,
(b) PbS+40=PbS04 (anglesite);
(c) FeS2+70+H20=H2S04+FeS04
(2) These may react with the limestone as follows
(smithsomte) (gypsum)
(a) ZnS04+CaC03+2H20=ZnC03 + CaS04 2H20,
(cerussite) (gypsum)
(b) PbS04+CaCO3+2H20=PbC03 + CaS04
(3) Some of the sulphates and carbonates carried down into the un- altered sulphides may react with these, yielding
Galena) (a) PbS04+FeS2+02=PbS+FeS04+S02,
(galena) (sidente) (J) PbC03+FeS2+02=PbS + FeCOs + S02;
(galena) GO PbS04+ZnS PbS+ZnS04,
(galena) (smithsonite) (<0 PbC03+ZnS PbS + ZnC03
The PbS replacing the ZnS and deposited in the cracks in the original mixture of PbS, ZnS and FeS2 increases the percentage of this compound in the vein and thus enriches it.
There is also an increase in the percentage of ZnS brought about by the reactions between the zinc salts (ia and 20), and the pyrite, analogous to those between the lead salts and pyrite (30 and 36) Thus
(sphalerite) ZnS04+FeS2+02 ZnS + FeS04+S02,
(sphalerite) ZnC03+FeS2+02 ZnS + FeC03+S02.
Formation Of Minerals 35
The zinc salts produced in reactions $c and $d if carried downward will also have the opportunity to react the pynte in the same way
If the ZnS is deposited in fissures in the vein matter this will tend to enrich it with zinc
The oxidized zone contains (smithsonite) ZnCOs, (anglesite) PbSO4, (cerussite) PbCOa and (limomte) Fe2(OH)2 The ZnS04, formed also in the oxidized zone, is so readily soluble in water that it is leached from the other oxidized compounds and is carried downward.
Part Ii Descriptive Mineralogy
Chapter Iii
Introduction— The Elements
OF the 1,000 or more distinct minerals recognized by mineralogists only a few (some 250) are common A few are important because they constitute ores, others because they are components of rock masses, and others simply because of their great abundance Only a few miner- alogists profess acquaintance with more than 500 or 600 minerals The majority are familiar with but 300 or 400, relying for the identification of the remainder upon the descriptions of them recorded in mmeralogical treatises
Only the minerals commonly met with and those of economic or of special scientific importance are described m this book They should be studied with specimens before one, in order that the relation between the descriptions and the objects studied may be forcibly realized Min- eralogy cannot be studied successfully from books alone It is primarily a study of objects and consequently the objects should be at hand for inspection l
Mineral Names. — The names of the great majority of minerals end in the termination "ite " This is derived from the ancient Greek suffix "itis" which was always appended to the names of rocks to signify that they are rocks The first portion of the name, to which the suffix is added, either describes some quality or constituent possessed by the mineral, refers to some common use to which it has been put, indicates the locality from which it was first obtained, or is the name of some person intended to be complimented by the mineralogist who first described the mineral bearing it
1 Collections of the common minerals in specimens large enough for convenient study may be secured at small cost from any one of the mineral dealers whose addresses may be found m any mmeralogical journal
Introduction— The Elements 37
The following examples taken from Dana illustrate some of these principles The mineral hematite (Fe203) is so named because of the red color of its powder, chlorite (a complicated silicate), because of its green color, sidente (FeCOs), from the Greek word for iron, because it con- tains this metal, magnetite (FeaO-i) after Magnesia in Asia, goethite (FeO(OH)) after the poet Goethe
The names of a few minerals end in "ine," "ane," ase," ote," etc , but the present tendency is to ha\ e them all end in "ite " Occasionally, the same mineral may have two names This may be due to the fact that it was discovered by two mineralogists working at the same tune in different places, or it may be due to the fact that the mineralogists of different countries prefer to follow different precedents set by the old mineralogists of their respective nationalities For example, the min- eral (Mg Fe)sSi04 is called ohmne by the Germans and by most English- speaking mineralogists, and peridot by the French The Germans follow the German mineralogist Werner, who first used the name ohvine in 1789, while the French follow the French teacher Hauy, who proposed the name peridot in 1801
Elements
The elements that occur in nature are few in number, and these, with rare exceptions, do not occur in great abundance They may be separated into the following groups the carbon group, the sulphur group, the arsenic group, the silver group, and the platinum-iron group Some of these comprise only a single mineral, while others comprise six or seven Only a portion of these are described
The Non-Metals And Metalloids
Carbon Group
The carbon group embraces several minerals of which one is dia- mond, another is an amorphous black substance known as schungite, and the other two are apparently but different forms of graphite The element may thereupon be regarded as tnmorphous Diamond and graphite are both important.
Isometric (hextetrahedral) Hexagonal (ditngonal scalenohedral)
Diamond Graphite
Diamond (C)
The diamond is usually found in distinct crystals or in irregular masses, varying m size from a pin's head to a robin's egg In some cases large individual pieces are found but they "-are exceedingly rare
Descriptive Mineralogy
FIG ii — Etch Figures on Cubic Face of Diamond Crystal (After Tscher- mak)
The largest ever found, known as the Cullman diamond (Fig 16), weighed 3,024! carats or 621 grams, or i 37 Ib , and measured 112x64x51 mm It was cut into nine fine gems and a number of smaller ones (Fig 17)
In composition the diamond is pure car- bon, but it is a form of carbon that is not ignited and burned at low temperatures At high temperatures, however, especially when in the presence of oxygen, it burns freely with the production of CC>2, and, in the case of opaque varieties, a little ash
Its crystallization is isometric (hextetra- hedral class), and the forms on the crystals often appear to be tetra- hedrally hemihedral, although the etch figures on cubic faces suggest hexoctahedral symmetry (Fig n). Octahedrons, tetrahedrons, icositet- rahedrons and combinations of these forms are common, and in nearly all cases the interf acial edges are rounded and the crystal faces curved Some- times this curving is so pronounced that the individuals are practically spheres (Fig 12) Twins are com- mon with 0(in) as the twinning plane (Fig 13),
The cleavage of diamond is per- fect parallel to the octahedral face. This is an important characteristic, as the lapidary makes use of it in the preparation of stones for cutting Its fracture is conchoidal Its specific gravity is 3 52 and its hardness greater than that of any other known substance Most diamonds are dark and opaque, or, at most, translucent, but many are found that are transparent and color- less or nearly so Gray, brown, green, yellow, blue and red tinted stones are also known, and, with the exception of the blue and red diamonds, these are more common than the colorless, or luster of all diamonds is adamantine, and
FIG 12 — Crystal of Diamond with Rounded Edges and Faces (Krantz )
FIG 13 — Octahedron of Diamond Twinned aboutO(m)
so-called white stones
Introduction—The Elements 39
their index of refraction is very high, n=z 4024 for red rays, 2 4175 for yellow rays, and 2 4513 for blue ra>s In consequence of their strong dispersion, the reflection of light from the inner surfaces of transparent stones is very noticeable, causing them to sparkle brilliantly, with a handsome play of colors It is this latter fact and the great hardness of the mineral that make it the most valuable of the gems The mineral is a nonconductor of electricity
Three varieties of the diamond have received distinct names in the trade These are
Gem diamonds, which are the transparent stones,
Bort, or Bortz, gray or black translucent or opaque rounded masses, with a rough exterior and the structure of a crystalline aggregate, and
Carbonado, black, opaque or nearly opaque masses possessing a crystalline structure, but no distinct cleavage
The only minerals with which diamond is liable to be confused are much softer, and, consequently, there is little difficulty in dis- tinguishing between them
Syntheses — Small diamonds have been made by fusing in an electric furnace metallic iron containing a small quantity of carbon and cooling the mass suddenly in a bath of molten lead They have also been made by heating in the electric arc pulverized carbon on a spiral of iron wire immersed m hydrogen under a pressure of 3,100 atmospheres A third method, which resulted in the production of tiny octahedrons, consisted in melting graphite in olivine, or in a mixture of silicates having the composition of the South African " blue ground," with the addition of a little metallic aluminium or magnesium
Occurrence and Origin — Diamonds are found (i) in clay, sand or gravel deposits or in the rocks formed by the consolidation of these substances, where they are associated with gold, platinum, topaz, garnet, tourmaline and with other minerals that result from the decom- position of granitic rocks, (2) in a basic igneous rock containing frag- ments of shale (a consolidated mud) and (3) small diamonds have been discovered in meteorites
The manner of origin of diamonds has been a subject of contro- versy for many years The most popular theory ascribes the diamonds in igneous rocks to the solution of organic matter m the rock magmas and the crystallization of the carbon upon cooling Another theory regards the carbon as an original constituent of the magma. The diamonds in sand, sandstone, granite, etc , are believed to have been transported from their original sources and deposited in river channels or on beaches.
40 Descriptive Mineralogy
Localities — The principal localities from which diamonds are obtained are the Madras Presidency in India, the Province of Mmas-Geraes in Brazil, the Island of Borneo, the valleys of the Vaal and Orange Rivers, and other places in South Africa, and the valley of the Mazarum River and its tributaries in British Guiana Recently diamond fields have been discovered in New South Wales, Australia, in the \alley of the Kasai River m the Belgian Kongo, in Arkansas, and in the Tula- meen district, British Columbia
In the United States a few gem diamonds have been found from tune to time in Franklin and Rutherford counties in North Carolina, in the gold-bearing gravels of California, and m soils and sands in the states of Alabama, Virginia, Wisconsin, Indiana, Ohio, Idaho anl Oregon A stone (the Dewey diamond) found near Richmond, Virginia, a few years ago is valued at $300 or $400
The principal source of diamonds and carbonado in Brazil at the present time is Bahia, where the mineral occurs in a friable sandstone along river courses The output of this region has decreased so greatly in the last few years that although a mass of carbonado weighing 3,073 carats (the largest mass of diamond material ever found) was obtained in 1895, the price of this impure diamond rose from $10 50 per carat m 1894 to $36 oo per carat in 1896 and $85 oo per carat for the best quality m 1916
The only diamond field of prominence m the United States is that which has recently been exploited near Murfreesboro in Arkansas, where the conditions are similar to those existing in South Africa The dia- monds occur m a basic igneous rock (pendotite) that cuts through Scind- stones and quartzites The pendotite is weathered to a, soft earth or " ground " m which the diamonds are embedded Up to the end of 1914 over 2,000 diamonds had been found, mostly small stones weighing in the aggregate 550 carats, valued at about $12,000 One, however, weighed 8§ carats and another carats The rough unsorted stones are valued at $10 per carat Three stones that were cut were found to be worth from $60 to $175 per carat The district has not yet been sufficiently developed to prove its commercial value The diamonds in British Columbia occur in the same kind of rock as those m Arkansas The few that have thus far been found are too small for any practical use
In former times the mines of India and Borneo were very produc- tive, the famous Golconda district m India for a long period furnishing most of the gems to commerce
The African mines were opened in 1867 Since this time they
— mil, Ji/JjJkMIiJWTS 41
have been practically the only producers of gem material in the world It is estimated that the quantity of uncut diamonds yielded by the mines near Kimberly alone have amounted in value to the enormous sum of $900,000,000 The output of the African mines in 1913 was sold for about $53,000,000, being over 95 per cent of the world's out- put of gem material Of this amount about $9,000,000 worth of stones were furnished by German Southwest Africa, the balance by the Union of South Africa The diamonds are found in a pendotite which occurs in the form of volcanic necks, or " pipes," cutting carbonaceous shales The igneous rock is much weathered to a soft blue earthy mass known as " blue earth " Near the surface where exposed to the action of the atmosphere the earth is yellow The diamonds are scattered through the weathered material in quantities amounting to between 3 and 6 carat per cubic yard
E\tr action — Where the diamond occurs in sand and gravel it is ob- tained by washing away the lighter substances
In South Africa and Arkansas the mineral is found in a basic volcanic rock which weathers rapidly on exposure to the air The weathered rock is mined and spread on a prepared ground to weather When suf- ficiently disintegrated water is added to the mass and the mud thus formed is allowed to pass over plates smeared with grease The dia- monds and some of the other materials adhere to the grease, but most of the valueless material is carried off by the water
Uses — Transparent diamonds constitute the most valuable gems in use Perfectly white stones, or those possessing decided tints of red, rose, green or blue are the most highly prized They are sold by weight, the standard being known as the carat, which, until recently, was equivalent to 3 168 grains or 205 milligrams At present the metric carat is m almost universal use This has a weight of 200 milligrams The price of small stones depends upon their color, brilliancy and size — a perfectly white, brilliant, cut stone weighing one carat, being valued at about $175 oo As the size increases the value increases in a much greater ratio, the price obtained for large stones depending almost solely upon the caprice of the purchaser
Nearly all the gem diamonds put upon the market are cut before being offered for sale The chief centers of diamond cutting are Ant- werp and Amsterdam in the Old World and New York in America The favorite cuts are the brilliant and the rose For the former only octahedral crystals, or those that will yield octahedrons by cleavage, are used, for the rose cut distorted octahedrons or twinned crystals In producing the "brilliant" a portion of the top of an octahedron is cut
Descriptive Mineralogy
off and a small portion of the bottom On the remainder are cut three or four bands of facets running horizontally around the stone (see Fig 14) The "rose" has a flat base surmounted by a pyramidal dome consisting of 24 or more facets In late years the shapes into which diamonds are cut have been determined less by the decrees of fashion and more by the
desire to sa\e as much ma- terial as possible, and, conse- quently, irregularly shaped cut diamonds are much more common than formerly (com- pare Fig 17).
Diamonds are employed also as cutting tools Small fragments, or splinters of gem quality, are used for cutting and polishing diamonds and
Rose
Grona Back, or Pavilion
Step or Trap
Crown
Side View
Pavilion, or Base
Brilliant FIG 14 — Principal " cuts " of Diamonds
other gems, and small crystals with crystal edges for cutting glass Small cleavage pieces are utilized in the manufacture of engravers' tools and writing instru- ments Recently diamonds with small holes of from 008 to 0006 of an inch drilled in them, have been employed as wne dies
Bort is also used as a polishing and cutting material, while carbonado, nearly all of which comes from Brazil, is used in the manufacture of boring instruments Diamond drills consist of hollow cylinders of soft iron set at their lower edges with 6, 8 or 12 black diamonds By rapid revolution of this a "core" may be cut from the hardest rocks
Some Famous Diamonds — The largest diamond ever found — the Cull- inan— was picked up at the Premier Mine (Fig 15) in the Transvaal in January, 1905, and was presented to King Edward of England as a birth- day gift in 1908 (Figs 16 and 17 ) It weighed about 3,025 carats (about i 37 pounds) The next largest was found in June, 1893, at the Jagers- fontem mine It is known as the Excelsior It weighed in its natural state 971 carats and was 3 inches long in its greatest dimension It was valued at $2,000,000 It is said to have been presented by the Presi- dent of The Orange Free State to Pope Leo XIII The third largest stone is the Reitz It is a 640-carat stone found at the same mine during the close of 1895 This, though smaller, is said to be handsomer than the Excelsior The most noted diamond in the world is the Kohmoor, which weighed, before cutting, 186 carats It is now a brilliant of 106 carats, belonging to the crown of England Other famous diamonds aie the
Introduction— The Elements
FIG 15, — Premier Diamond Mines in South Africa
pIG X6,— -The Cullman Diamond. (Natural size )
Descriptive Mineralogy
FIG 17 — Gems Cut from the Cullman Diamond (Two-lifthb nat si/c )
Orlov, 193 carats, the property of Russia, the Regent or Pitt diamond of 137 carats belonging to France, the Green diamond of Dresden,
weighing 48 carats, and the Blue Hope diamond, weighing 44 carats The " Star of the South," found in Brazil, weighed 254 carats bcfoie cutting and 125 .iftcnvard The Victoria diamond from one of the Kimberly mines -weighed 457 carats found It has been cut to a perfect brilliant of 180 carats valued at $1,000,000 The Tiffany dia- mond (Fig 1 8) now owned in New York is a double brilliant of a golden yellow color weighing 128 carats (25 702 grams) and valued at $100,000 When it is remembered that a five-carat stone is large, the enormous proportions of the above-named gems are better appreciated.
FIG 1 8 —-The Tiffany Diamond (Nat- ural size ) (Kindness of TiJJany Co )
Graphite (C)
Graphite, or plumbago, occurs principally in amorphous masses of a black, clayey appearance, in radiated masses, in brilliant lead black scales or plates, and occasionally in crystals with a rhombohedral habit
Like diamond, graphite consists of carbon Crystals from Ceylon yield C=794o, Ash=is 50, Volatile matter=s 10. The mineral is often impure from admixture with clay, etc.
Introduction— The Elements 45
Crystals of the material are so rare that their symmetry is still in doubt Their habit is hexagonal (ditngonal scalenohedral class) Measurements made on the interfacial angles of crystals from Ticon- deroga, New York, gave a c=i i 3859 These possess a rhombo- hedral symmetry All crystals are tabular and nearly all are so distorted that the measurements of their interfacial angles cannot be depended upon for accuracy They apparently contain the planes R(ioTi),
OP(IOOO), COP2(II20), and 2P2(lI2l)
Graphite is black and earth} , or lustrous, according as it is impure or pure It is easily clea\ able parallel to the basal plane and the cleav- age laminae are flexible It is very soft, its hardness being only 1-2, its density about 2 25 Its luster is metallic and the mineral is opaque even in the thinnest flakes It is a conductor of electricity
Graphite is infusible and noncombustible even at moderately high temperatures Like diamond, however, it may be burned under cer- tain conditions at ery high temperatures (65o°-7oo°) It is unaffected by the common acids and is not acted upon by the atmosphere When, ho\\e\er, it is subjected to the action of strong oxidizing agents, such as a mixture of potassium chlorate (KClOj) and fuming nitric acid, it changes to a substance knon as graphitic acid (CnKLiOj) It is thus distinguished from amorphous carbon, like schungite and anthracite Moreo\er, man\ forms of graphite, moistened with fuming nitric acid and heated, s\\ell up and send out worm-like processes Those \\hich do not act thus are called graphititc Natural graphite is of both types
Its color, softness and infusibility serve to distinguish graphite from all other minerals but molybdenite (p 75) It ma\ be distinguished from this mineral by the fact that it contains no sulphur
Syntheses — Crystalline graphite is made on a commercial scale by treating anthracite coal or coke containing about 5 75 per cent of ash in an electric furnace It also separates molten iron con- taining dissolved carbon is cooled
Occurrence and Origin — Graphite occurs as thin plates and scales m certain igneous rocks, m gneisses, schists and limestones, as large scales m coarse granite dikes (pegmatite) and m crystalline limestones, and as amorphous masses at the contacts of igneous rocks with carbona- ceous rocks The mineral is also found in veins cutting sedimentary and metamorphic rocks Crystals are found only in limestone
The occurrence of graphite m sedimentary and igneous rocks sug- gests that it may have been formed m several ways It is thought that the material in limestone and quartz-schist may represent carbo-
46 Descriptive Mineralogy
naceous material that was deposited with the sediments and which has since been carbonized by heat and pressure The material m peg- matite may be an original constituent of the magma that produced the rock, and the graphite may be the product of pneumatolytic processes , i c , it may have been produced by deposits from vapors that accom- panied the formation of the pegmatite If this be true, the mineral found in metamorphosed limestone and schist may be of contact origin, i e , it may have been produced by the migration of gases and solutions from igneous rocks into the mass of the surrounding sediments The vein deoosits probably had a similar origin, the mineral having been deposited mainly in cracks traversing metamorphic rocks On the other hand, graphite, in some instances, appears to be a direct separa- tion from a molten magma
Localities — The principal foreign source of supply for commercial graphite is the Island of Ceylon In the United States the mineral has been mined on the southeast side of the Adirondacks in New York, in Chester County, Pennsylvania, near Dillon, Montana, at several points in Arkansas, Georgia, Alabama and North Carolina, in Wyo- ming, in Baraga County, Michigan, and to a small extent in Colorado, Nevada, and Wisconsin It occurs also abundantly at many other places Its chief source in the United States is Graphite, near Lake George, New York
Preparation — Graphite is obtained on a commercial scale by grind- ing the rock containing it and floating the graphite flakes
Uses —Crude graphite, or plumbago, is used in the manufacture of stove and other polishes, and of black paint foi metal surfaces, for both of which it is especially valuable on account of its noncorrodmg propri- ties The purified mineral is mixed with clay and made into crucibles for use at high temperatures It is also ground and used m this form as a lubricant for heavy machinery, and is compressed into u black lead " centers for lead pencils
Production —The quantity of crude graphite mined m the United States during 1912 amounted to 2,445 tons> valued at $207,033, besides which there were manufactured 6,448 tons, valued at $830,193. The imports were 25,643 tons, valued at $709,337
Schungjte is a black, amorphous carbon with a hardness of 3-4 and a . of i 981 It is soluble in a mixture of HNOs and KClOj without the production of graphitic acid. It occurs in some crystalline schists.
Introduction— The Elements
Sulphur Group
Sulphur is known in at least six different forms, four of which are crystalline The two best known forms crystallize respectively in the orthorhombic (orthorhombic bipyramidal class) and the monoclimc (prismatic class) systems The former separates from solutions of sulphur in carbon bisulphide and the latter separates from molten masses Both the orthorhombic and the monoclimc phases are believed to be formed by natural processes, but the latter passes over into the former upon standing, so that its existence as a mineral cannot be definitely proven Selenium and tellurium, which are also members of the sul- phur group, are extremely rare Tellurium occurs in rhombohedral crystals and selenium in mixed crystals of doubtful character with sulphur and tellurium
Sulphur (S)
Sulphur occurs in nature as a lemon-colored powder, as spherical or globular masses, as stalactites and in crystals
Chemically it is pure sulphur, or a mixture of sulphur and clay,
Fig 19 Fig 20
FIG 19— Sulphur Crystals with P, in (£), 3?, 113 (s), P°, on and oP,
ooi (c)
FIG 20 —Distorted Crystal of Sulphur (Forms same as in Fig. 19 )
bitumen or other impurities. It sometimes contains traces of tellu- rium, selenium and arsenic
Crystals of sulphur are usually well formed combinations of ortho- rhombic bipyramids and domes, with or without basal terminations. Their axial ratio 8108 i i 9005 The principal forms observed are P(in), POO(IOI), P £6(011), iP(ii3) and oP(ooi) (Figs 19 and 20) The habit of the crystals is usually pyramidal, though crystals with a tabular habit are quite common
Crystals of sulphur are yellow Their streak is light lemon yellow,
48 Descriptive Mineralogy
The mineral has a resinous luster Its hardnebs is only i 5-2, and density about 204 Its fracture is conchoidal and cleavage imper- fect It is transparent or translucent, is brittle and is a non- conductor of electricity Its indices of refraction for sodium light area i 9579, j8a 0377, 7 2 2452
Massive sulphur varies in color from yellow to yellowish brown greenish gray, etc , according to the character and amount of impurities it contains Its powder is nearly always crystalline In mass it pos- sesses a lighter color than the crystals or the massive sulphur
At a temperature of 114° sulphur melts, and at 270° it ignites, burning with a blue flame and evolving fumes of SO 2 At about 97° it passes over into the monoclimc phase It is insoluble in water and acids, but is soluble in oil of turpentine, carbon bisulphide and chlo- roform
There are few minerals that are apt to be mistaken for sulphur. From all of them it may be distinguished by its bnttleness and by the fact that it melts readily and burns with a nonlummous blue flame
Syntheses — Crystals with the form of the mineral are produced by the evaporation of solutions of sulphur in carbon bisulphide, and also by sublimation from the fumes of ore roasters
Occurrence and Origin — Sulphur occurs most abundantly m regions of active or extinct \olcanoes, and in beds associated with limestone and gypsum (CaSO* 2H20) In volcanic regions it is produced by reactions between the gases emitted from the volcanoes, or by the reac- tions of these with the oxygen of the air (seep 18) The deposits in gypsum beds may result from reduction of the gypsum by organic matter. Sulphur is formed also as a decomposition product of sulphides
In Iceland and other districts of hot springs sulphur is often deposited in the form of powder as the result of reactions similar to those that take place between the gases of volcanoes These hot springs are always connected with dying volcanoes, being frequently but the closing stages of their existence
Localities — The localities at which sulphur is known to exist are very numerous Those of commercial importance are Girgenti m Sicily, Cadiz in Spam, Japan, and in the United States, at the geysers 'of the Napa Valley, Sonoma County, and at Clear Lake, Lake County, California, at Cove Creek, Millard County, Utah, at the mines of the Utah Sulphur Company in Beaver County, in the same State, at Thermopohs, Wyoming, and at various hot springs in Nevada The mineral occurs also abundantly in the Yellowstone National Park, but cannot be placed on the market because of high transportation charges
Introduction— The Elements 49
Its principal occurrence m the United States is at Lake Charles in Calcasieu Parish, La , where it impregnates a bed of limestone at a depth of from 450 to 1,100 feet It occurs also abundantly in the coastal districts of Texas Here it is associated with gypsum
Extraction — Sulphur, when mined, is mixed with clay, earth, rock and other impurities Until recently it was purified by piling in heaps and igniting A portion of the sulphur burned and melted the balance, which flowed off and was caught A purer product is ob tamed by dis- tillation "Flowers of Sulphur" are made in this way At present much of the sulphur is extracted by treating the impregnated rock m retorts with steam under a pressure of 60 pounds and at a temperature of 144° C The sulphur melts and flows to the bottom of the retorts from which it is drawn off
In Louisiana and Texas, superheated steam is forced downward into the sulphur-impregnated rocks. This melts the sulphur, which con- stitutes about 70 per cent of the rock mass The melted sulphur is forced to the surface and caught in wooden bins The crude material has a guaranteed content of over 99! per cent sulphur
Uses — Sulphur, or brimstone, is used m the manufacture of some kinds of matches, m making gunpowder, and m vulcanizing rubber to increase its strength and elasticity It is used extensively in the manufacture of sulphuric acid, but is rapidly giving way to pynte for this purpose It is also utilized for bleaching straw, in the man- ufacture of certain pigments, among \\hich is vermilion, and in the preparation of certain medicinal compounds
Production — Most of the domestic product is at present from the Calcasieu Pansh, La , where about 300,000 tons are mined annually. New mines have been opened near Thermopolis in Wyoming, in Bra- zona County, Texas, and at Sulphur Springs, Ne\ada. The total amount of the mineral mined in 1912 was 303,472 tons, valued at $5,256,- 422 Besides, there were imported about 29,927 tons valued at $583,974, most of which came from Japan Sicily is the largest producer of the mineral, extracting about 400,000 tons annually.
Arsenic Group
The arsenic group comprehends metallic arsenic, antimony, bismuth and (according to some mineralogists), tellurium, besides compounds of these metals with each other They all crystallize in the rhombo- hedral division of the hexagonal system (ditrigonal scalenohedral class). The only members of the group that are at all common are arsenic and antimony
50 Descriptive Mineralogy
Arsenic (As)
Arsenic is rarely found in crystals It usually occurs massive or in botryoidal or globular forms
Specimens of the mineral are rarely pure They usually contain some antimony, and traces of iron, silver, bismuth, and other metals
The crystals are cubical in habit, with an axial ratio of i . i 4025 The principal forms observed are oR(oooi), R(ioTi), JR(ioT4), — |R(oil2) and —(0332) Twins are rare, with -|R(oil2) the twinning plane
Arsenic is lead-gray or tin-white on fresh fractures, and dull gray or nearly black on surfaces that have been exposed for some time to the atmosphere
Crystals cleave readily parallel to the base The fracture of massive pieces is uneven The mineral is brittle Its hardness is 3 5 and its density 5 6-5 7 Its streak is tin-white tarnishing soon to dark gray It is an electrical conductor
Arsenic may easily be distinguished from nearly all other minerals, except antimony and some of the rarer metals, by the color of its fresh surfaces From these, with the exception of antimony, it is also readily distinguished by its action on charcoal before the blowpipe, when it volatilizes completely without fusing, at the same time tmgeing the flame blue and giving rise to dense white fumes of As20s, which coat the charcoal The fumes of arsenic possess a very disagreeable and oppres- sive odor, while those of antimony have no distinct odor
Syntheses — Arsenic has been obtained in crystals by subliming arsenic compounds protected from the air It has also been obtained m the wet way by heating realgar (As2Sa) with sodium bicarbonate at 300° C
Occurrence and Origin — Arsenic often accompanies ores of antimony, silver, lead and other metals in veins in crystalline rocks, especially in their upper portions, where it was formed by reduction from its com- pounds
Locahties — The silver mines at Freiberg, and other places m Saxony afford native arsenic in some quantity It is found also in the Harz, at Zmeov in Siberia, in the silver mines of Chile and elsewhere.
Within the boundaries of the United States arsenic occurs only in small quantity at Haverhill, N H , at Greenwood, Me , and at a silver and gold mine near Leadville, Colo
Uses— Arsenic is used only in the forms of its compounds The native metal occurs too sparingly to be of commercial importance.
Introduction— The Elements 51
Most of the arsenic compounds used in commerce are obtained from smelter fumes produced by smelting arsenical copper and gold ores
Antimony (Sb)
Antimony is more common than arsenic, which it resembles in many respects It is generally found in lamellar, radial and botryoidal masses, though rhombohedral crystals are known
Most antimony contains arsenic and traces of silver, lead, iron and other metals
Its crystals are rhombohedral or tabular in habit, and have an axial ratio of a : c=i . i 3236 The forms observed on them are the same as those on arsenic with the addition of ocP2(ii2o), and several rhombohedrons Twinning is often repeated The cleavage is perfect parallel to oP(oooi)
Antimony exhibits brilliant cleavage surfaces with a tin-white color On exposed surfaces the color is dark gray The mineral differs from arsenic in its greater density which is 6 65-6 72, and in the fact that it melts (at 629°) before volatilizing Its fumes, moreover, are devoid of the garlic odor of arsenic fumes
Syntheses — Crystals of antimony are often obtained from the flues of furnaces in which antimomal lead is treated. They have also been made by the reduction of antimony compounds by hydrogen at a high temperature
Occurrence and Localities — Antimony occurs in lamellar concretions in limestone near Sala, Sweden, and at nearly all of the arsenic localities mentioned above, especially in veins containing stibnite (Sb2Ss) or silver ores It is found also in fairly large quantities in veins near Fredencton, York County, New Brunswick, in California and elsewhere
Uses — Although the metal antimony is of considerable importance from an economic point of view, being used largely in alloys, the native mineral, on account of its rarity, enters little into commerce Some of the antimony used m the arts is produced from its sulphide, stibnite (see p 72) Most of the metal, however, is obtained in the form of a lead-antimony alloy in the smelting of lead ores and the refining of pig lead
Bismuth (Bi) is usually in foliated, granular or arborescent forms, and very rarely in rhombohedral crystals, with a . c=i ' i 3036 It is silver-white with a reddish tinge, is opaque and metallic Its streak is white, its hardness 2-2 5 and density 98 It fuses at 271°. On charcoal it volatilizes and gives a yellow coating It dissolves in HNOs When
52 Descriptive Mineralogy
this solution is diluted a white precipitate results The mineral occurs in veins with ores of silver, cobalt, lead and zinc It is of no commercial importance Most of the metal is obtained in the refining of lead In 1913 the United States produced 185,000 Ibs and Bolivia about 606,000 Ibs
Tellurium (Te) usually occurs in prismatic crystals with a tin-white color and in finely granular masses in veins of gold and silver ores, especially sulphides and tellundes Its hardness is 2 and density 6 2 Before the blowpipe it fuses, colors the flame green, coats the charcoal with a white sublimate bordered by led, and yields white fumes
The mineral tellurium is of little value as a source of the metal Most of that used in the arts is obtained as a by-product in the elec- trolytic refining of copper made from ores containing tellundes and from the flue dust of acid chambers and smelting furnaces The United States, in 1913, produced about 10,000 Ibs of tellurium and selenium, valued at $3,000
The Metals
The metallic elements occur as minerals m comparatively small quan- tity, most of the metals used in the industries being obtained from their compounds Iron, the most common of all the metals used in com- merce, is rare as a mineral, as are also lead and tin Silver, copper, gold and platinum are sufficiently important to be included in our list for study Gold and platinum are known almost exclusively in the metallic state A large portion of the copper produced in this country is also native, and some of the silver
Silver, copper, lead, gold, mercury and the alloys of gold and mer- cury crystallize in distinct crystals belonging to the isometric system (hexoctohedral class) Platinum, as usually found, is in small plates and grains Crystals, however, have been described and they, too, are isometric Platinum and iron are separated from the other metals and, together with the rare alloys of platinum with indium and osmium, are placed in a distinct group which is dimorphous The reason for this is that platinum, although isometric in crystallization, often contains notable traces of indium, which in its alloy with osmium is hexagonal (rhombohedral) Indium, thus, is dimorphous, hence platinum which forms crystals with it and is, therefore, isomorphous with it, must also be regarded as dimorphous The various platinum metals thus com- pnse an isodimorphous group Iron is placed in the same group because it is so frequently alloyed with platinum The metals are, therefore, divisible into two groups, one of which comprises the metals named at
Introduction— The Elements
the beginning of this paragraph and the other consists of the rare metals, palladium, platinum, indium, osmium, iron and their alloys The metal tin, which is tetragonal m its native condition, constitutes a third group, but since it is extremely rare it will not be referred to again
Gold Group
This group embraces the native metals, copper, siker, gold, gold- amalgam (Au Hg), siher-amalgam (Ag Hg), mercury, and leal All crystallize in the isometric system (hexoctahedral class), and all form twins, with 0(in) the twinning plane Copper, silver and gold are the most important
Copper (Cu)
Most of the copper of commerce is obtained from one or the other of its sulphides A large portion, however, is found native This occurs m tiny grams and flakes, in groups of crystals and in large masses of irregular shapes
In spite of its softness copper is better crystallized than either gold or silver It is true that its crystals are usually flattened and otherwise distorted, but, nevertheless, planes
can very frequently be detected upon them
rr.i - i , -, / FIG 2i.— Copper Crystal
The principal forms observed are oo O oo (100), M Q ,
oo O(no), 0(ni), and various tetrahexahedra 20 & 1 2io' (h).
and icositetrahedra. (Figs. 21 and 22 ) Some- times the crystals are sim- ple, in other cases they are twinned parallel to O Often they are skeleton crystals Groups of crys- tals are very common These possess the arbo- rescent forms so frequently seen in specimens from Keweenaw Point in Mich- igan, or are groupings of simple forms extended in the direction of the cubic
FIG. 22. — Crystal of Copper from Keweenaw Point, Mich , with wO(iio) and 202(211)
axes.
Copper is very ductile and very malleable Its hardness is only
54 Descriptive Mineralogy
2 5-3 and its density about 88 It possesses no cleavage, and its frac- ture, like that of the other metals, is hackly In color it is copper-red by reflected light, often tarnishing to a darker shade of red In very thin plates it is translucent with a green color The metal fuses at 1083° and easily dissolves in acids It is an excellent conductor of elec- tricity
Its most characteristic chemical reaction is its solubility in nitric acid with the evolution of brownish red fumes of nitrous oxide gas
Copper may easily be distinguished from all other substances except gold and a few alloys by its malleability and color It is distinguished from gold by the color of its borax bead and by its solubility in nitric acid with the production of a blue solution which takes on an intense azure color when treated with an excess of ammonia From the alloys that resemble it, copper may be distinguished by its greater softness and the fact that it yields no coatings when heated on charcoal, while at the same time its solution in nitric acid yields the reaction described above
Syntheses — Copper crystals separate upon cooling solutions of the metal in silicate magmas and upon the electrolysis of the aqueous solu- tions of its salts
Occurrence — The principal modes of occurrence of the metal are, (i) as fine particles disseminated through sandstones and slates, (2) as solid masses filling the spaces between the pebbles and boulders making up the rock known as conglomerate, (3) in the cavities in old volcanic lavas, known as amygdaloid, (4) as crystals or groups of crystals imbedded m the calcite of veins, (5) in quartz veins cutting old igneous rocks or schists, and (6) associated with the carbonates, malachite and azurite, and with its different sulphur compounds, in the weathered zone of many veins of copper ores
The copper that occurs in the upper portions of veins of copper sulphides is plainly of secondary origin That which occurs in conglom- erates and other fragmental rocks and in amygdaloids was evidently deposited by water, but whether by ascending magmatic water or by descending meteoric water is a matter of doubt
Localities — Native copper is found in Cornwall, England, in Nassau, Germany, in Bolivia, Peru, Chile and other South American countries, in the Appalachian region of the United States and in the Lake Superior region, both on the Canadian and the American sides
The most important district in the world producing native copper is on Keweenaw Point, in Michigan The mineral occurs mainly in a bed of conglomerate of which it constitutes from i to 3 per cent, though it is found abundantly also in sandstone and in the amygdaloidal cavities
Introduction— The Elements 55
of lavas associated with the conglomerates Veins of caicite, through which groups of bright copper en stals are scattered are also very plentiful in many parts of the district The copper is nearh always mixed with silver in visible grains and patches
Extraction and Refining —The rock containing the native metal is crushed and the metal is separated from the useless material by wash- ing The concentrates, consisting of the crushed metal mixed with particles of rock and other impurities are then refined by smelting methods or by electrolysis
Uses —The uses of copper are so many that all of even the important uses cannot be mentioned in this place Both as a metal and in the form of its alloys it has been employed for utensils and war implements since the earliest times In recent times one of its principal uses has been for the making of telegraph, telephone and trolley wires It is employed extensively in electroplating by all the great newspapers and publishers, and is an important constituent of the valuable alloys brass, bronze, bell metal and German silver Its compound, blue vitriol (copper sul- phate), is used in galvanic batteries, and its compounds with arsenic are utilized as pigments
Production — The world's production of copper amounted to 1,126,- ooo tons in 1912, but a large portion of this was obtained from its car- bonates and sulphides The quantity obtained from the native metal is unknown The contribution of the United States to this total was about 621,000 tons, valued at about $206,382,500, of which 115,000 tons was native copper from the Lake Superior region The largest single mass ever found in the Lake Superior region weighed 420 tons
Silver (Ag)
Silver is usually found in irregular masses, in flat scales, in fibrous dusters, and in crystal groups with arborescent or acicular forms Sometimes the crystals are well developed, more frequently they ex- hibit only a few distinct faces, but in most cases they are so distorted that it is difficult to make out their planes
Pure silver is unknown The mineral as it is usually obtained con- tains traces of gold, copper, and often some of the rarer metals, depend- ing upon its associations.
Ideally developed silver crystals are rare They usually show ooOoo(ioo), 006(110), 0(in) various tetrahexahedrons and other more complicated forms The majority of the crystals are distorted by curved faces and rounded edges, and many of them by flattening or
56 Descriptive Mineralogy
elongation The arborescent groups usually branch at angles of 60°, one of the characteristic angles for groups of isometric crystals Twins are quite common, with O(iii) the twinning plane
Silver is a white, metallic mineral when its surfaces arc clean and fresh As it usually occurs it possesses a gray, black or bluish black tarnish which is due to the action of the atmosphere or of solutions The tarnish is commonly either the o\ide or the sulphide of silvci
The mineral has no cleavage Its fracture is hackly II is soft (hardness 2-3), malleable and ductile, and is an excellent conductor of heat and electricity Its density is about 10 5, varying slightly with the character and abundance of its impurities It fuses at 960°
It is readily soluble in nitric acid forming a solution from which a white curdy precipitate of silver chloride is thrown down on the addition of any chloride This precipitate is easily distinguished from the corresponding lead chloride by its insolubility in hot water
Synthesis — Crystals bounded by 0(in) and °o 0 oo (100) have been made by the reduction of silver sulphate solutions, with sulphurous acid
Occurrence — Native silver is found in veins with calcite (CaCOO? quartz (8102), and other gangues traversing crystalline rocks, like granite and various lavas, and also in veins cutting conglomerates and other rocks formed from pebbles and sands It is also disseminated in small particles through these rocks It occurs invisibly disseminated in small quantities through many minerals, particularly sulphides, and visibly intermingled with native copper It is abundant in the upper weathered zones of many veins of silver-bearing ores, and m the zones of secondary enrichment in the same veins It also occurs in small quantity m placers In general, its origin is similar to that of gold (see p 59)
Localities — The localities in which silver is found are too numerous to mention Andreasberg in the Harz has produced many fine crys- tallized specimens The principal deposits now worked are at Cobalt in Canada, in Peru, in Idaho, at Butte, Montana, in Arizona and at many places m Colorado On Keweenaw Point, in Michigan, fine crystals have been found in the calcite veins cutting the copper-bearing rocks, and masses of small size in the native copper so abundant in the district Indeed some of the copper is so rich in silver that the ore was in early times mined almost exclusively for its silver content At present the silver is recovered from the copper in the refining process At Cobalt the mineral occurs m well defined veins one inch to one foot
Introduction— The Elements 57
or more in width, cutting a series of slightly inclined pre-Cambnan beds of fragmental and igneous rocks The \eins contain native silver, sulphides and arsenides of cobalt, nickel, iron and copper, caicite and a little quartz Many of the veins are so rich (Fig 23) that Cobalt has become one of the most important camps producing native silver in the world.
Extraction and Refining — Silver is obtained from placers in small quantity by the methods made use of in obtaining gold (see p 6i\ i e , by hydraulic mining When it occurs in quartz veins or m complex ores such as constitute the oxidized portion of ore-bodies, the mass may be crushed and then treated with quicksilver, which amalgamates with the native silver and gold, forming an alloy. Such ores are known
FIG. 23 — Plate of Silver from Confagas Mine Cobalt Dimensions 32X14X1 ins Weight 37 Ibs. (Photo by C W. Knight )
as free milling The silver is freed from the gold and other metals by a refining process. It is separated from native copper by electrolytic methods.
Uses — Silver is used in the arts to a very large extent Jewelry, ornaments, tableware and other domestic utensils, chemical apparatus and parts of many physical instruments are made of it It is used also in the production of mirrors and in the manufacture of certain compounds used in surgery and in photography Its alloy with copper forms the staple coinage of China, Mexico and most of the South American coun- tries, and the subsidiary (or small) coinage of most countries In the United States it is used in the coinage of silver dollars and of frac- tions of the dollar as small as the dime. The silver corns of the United States are nine-tenths silver and one-tenth copper, the latter metal being added to give hardness English corns contain i2| parts silver to one
58 Descriptive Mineralogy
part of copper In 1912 the world's coinage of silver consumed 161,- 763,415 02 , with a value after coinage of $171,293,000
Production —The total production of silver in the United States during 1912 was over 63,766,000 oz , valued at over $39,197,000, of which about $100,000 worth came from placers and $325,000 worth from the copper mines of Michigan The balance was obtained by smelting silver compounds and in the refining of gold, lead, copper and zinc ores The world's production of silver during 1912 was 224,488,- ooo oz , valued at over $136,937,000, but most of this was obtained from the compounds of silver and not from the native metal The proportion obtained from the mineral is not definitely known, but the production of Canada was more than 30,243,000 oz , valued at $17,672,000 and nearly all of this came from Cobalt, where the ore is native silver
Gold (Au)
A large portion of the gold of the world has been obtained m the form of native metal The greater portion of the metal is so very finely disseminated through other minerals that no sign of its presence can be detected even with high powers of the microscope Although present in such minute quantities it is very widely spread, many rocks con- taining it jn appreciable quantities Its visible grains, as usually found, are little rounded particles or thin plates or scales mixed with sand or gravel, or tiny irregular masses scattered through white vem- quartz
Native gold rarely occurs in well formed crystals The metal is so soft that its crystals are battered and distorted by very slight pressure. Occasionally well developed crys- tals, bounded by octahedral, dodecahedral FIG 24 -Octahedral Skele- and compllcated icositetrahcdral and tetra- ton Crystal of Gold with , t
Etched Faces hexahedral faces are met with, but usually
the crystals are elongated or flattened Skele- ton crystals (Fig. 24) and groups of crystals are more frequently found than are simple crystals. Twins are common, with O(iii) the twin- ning plane
As found in nature, gold is frequently alloyed with silver and it often contains traces of iron and copper and sometimes small quanti- ties of the rarer metals
Gold containing but a trace of silver up to 1 6 per cent of this metal
Introduction— The Elements 59
is known simply as gold When the percentage of silver present is larger it is said to be argentiferous When the percentage reaches 20 per cent or above the alloy is called clectru ,: Palladium, rhodium and bismuth gold are alloys of the last-named metal roth the rare metals palladium or rhodium or with the more common bismath
The color of the different varieties of the mineral varies from pinkish silver-white to almost copper-red Pure gold is golden yellow With increase cf silver it becomes lighter in color and T\ith increase in copper, darker The rich red-yellow ot much of the gold used in the arts is due to the admixture ot copper In very thin plates or lea\ es ( ooi mm ) gold is translucent a blue or green tint
Gold is soft, malleable and ductile Its luster is, of course, metallic and its streak, yellow When pure its density is 1943, its hardness between 2 and 3, and its fusing point 1062° The metal is insoluble in most acids, but it is readily dissolved in a mixture of nitric and hydro- chloric acids (aqua regia) It is not acted upon by water or the atmos- phere Its negative properties distinguish it from the other substances -which it resembles in appearance It is a good conductor of electricity.
Syntheses — Crystals of gold have been obtained by heating a solu- tion of AuCls in amyl alcohol, and by treating an acid solution of the same compound with formaldehyde
Occurrence — Native gold is tound in the quartz of veins cutting through granite and schistose rocks, or in the gravels and sands of rivers whose channels cut through these, and in the sands of beaches bordering gold-producing districts It is sometimes found in the compacted gravels of old river beds, in a rock known as conglomerate, and in sand- stones It is also present in small quantities in many volcanic rocks, and is disseminated through pyrite (FeS2) and some other sulphur com- pounds and their oxidation products
The gold in quartz veins occurs as grains and scales scattered through quartz irregularly, often in such small particles as to be invisible to the naked eye, or as aggregates of crystals in cavities in the quartz Pyrite is nearly always associated with the gold. On surfaces exposed to the weather the pyrite rusts out and stains the quartz, leaving it cavernous or cellular
Most of the world's supply of gold has come from placers. These are accumulations of sand or gravel in the beds of old river courses The sands of modern streams often contain considerable quantities of gold Many of the older streams were much larger than the modern ones draining the same regions and, consequently, their beds contain more gold This was originally brought down from the mountains or
60 Descriptive Mineralogy
highlands in which the streams had their sources The sands and gravels were rolled along the streams' bottoms and their greater portion was swept away by the currents into the lowlands The gold, however, being much heavier than the sands and pebble grains, merely rolled along the bottoms, dropping here and there into depressions from which it could not be removed As the streams contracted in volume the gold grains were covered by detritus, or perhaps a lava stream flowing along the old river channel buried them These buried river channels with their stores of sands, gravels and gold constitute the placers With the gold are often associated zircon crystals, garnets, diamonds, topazes and other gem minerals Alluvial gold is usually in flattened scales or in aggregates of scales forming nuggets Some of the nuggets are so large, 190 pounds or more in weight, that it is thought they may have been formed by some process of cementation after they were transported to their present positions
The gold-quartz veins are usually closely associated with igneous rocks, but the veins themselves may cut through sedimentary beds or crystalline schists The veins are supposed to have been filled from below by ascending solutions Metallic gold is also present m the oxi- dized zones of many veins of gold-bearing sulphides and m the zones of secondary enrichment At the surface the iron sulphides are oxidized into sulphates, leaving part of the gold m the metallic state and dissolv- ing another part which is carried downward and precipitated
Principal Localities — Vein gold occurs m greater or less quantity in all districts of crystalline rocks It has been obtained m large quantity along the eastern flanks of the Ural Mountains, this having been the most productive region in the world between the years 1819 and 1849 It has been obtained also from the Altai Mountains in Siberia, from the mountains m southeastern Brazil, from the highlands of many of the Central and South American countries, and from the western portion of the United States, more particularly from the western slopes of the Sierra Nevada Mountains and the higher portions of the Rocky Mountains In recent years auriferous quartz veins have been worked at various points m Alaska, at Porcupine, Ontario, and other points in Canada
The great placer mines of the world are in California, Australia and Alaska In Australia the principal gold mines are situated m the streams rising in the mountains of New South Wales and their extension into Victoria The valleys of 'the Yukon and other rivers m Alaska have lately attracted much attention, and in the past few years the beach sands off Nome have yielded much of the metal
The most important production at present is from South Africa
Introduction— The Elements 61
where the metal occurs in an old conglomerate In the opinion of some geologists this is an old beach deposit, in the opinion of others the gold was introduced into the conglomerate long after it had consolidated
The sands of many streams in Europe and in the eastern United States have for many years been "panned" or cashed for gold The South Atlantic States, before the discovery of gold m California, in 1849, yielded annually about a million dollars' worth of the precious metal All of it was obtained by working the gra\ els and sands of small rivers and rivulets Many of these streams have been worked o\er several times at a profit and the mining continues to the present day Small quantities of gold have also been obtained from streams in Maine, New Hampshire, Maryland and other Atlantic coast states
Extraction and Refining — Gold is extracted from alluvial sands and from placers by washing in pans or troughs The sand, gravel and foreign particles are carried away by currents of water and the gold settles down with other heavy minerals to the bottom of the shallow pans used in hand washing, or into compartments prepared for it in troughs when the processes are on a larger scale It is after- ward collected by shaking it with mercury or, quicksilver, m \\hich it dissolves The quicksilver is finally driven off by heat and the gold left behind Auriferous beach sands and many lake, swamp and mer sands are dredged, and the sand thus raised is treated by similar methods Sands containing as low as 15 cents' worth of metal per cubic yard can be worked profitably under f orable conditions
Where the gold occurs free (not disseminated through sulphides) in quartz the rock is crushed to a fine pulp -with -water and the mixture allowed to flow over copper plates coated \uth quicksilver The gold unites with the quicksilver and forms an alloy from which the mercury is driven off by heat The process of forming allo}s of silver or gold with mercury is known as amalgamation
When the gold is disseminated through sulphides, these are concen- trated, i e , freed from the gangue material by washing and then roasted This liberates the gold which is collected by amalgamation, or is dissolved by chlorine or cyanide solutions and then precipitated
Uses — Gold, like silver, is used in the manufacture of jewelry and or- naments, in the manufacture of gold leaf for gilding and in the produc- tion of valuable pigments such as the "purple of Cassms " It also con- stitutes the principle medium for coinage in nearly all of the most important countries of the world The gold coins of the United States contain 900 parts gold in 1,000. Those of Great Britain contain 916 66 parts, the remaining parts consisting of copper and silver The total
62 Descriptive Mineralogy
gold coinage of the United States mints from the time of their organi- zation to the end of the year 1912 amounted to $2,765,900,000 The gold coined in the world's mints in 1912 amounted m value to $360,- 671,382, and that consumed in arts and industries to $174,100,000 Jewelers estimate the fineness of gold in carats, 24-carat gold being pure Eighteen-carat gold is gold containing 18 parts of pure gold and 6 parts of some less valuable metal, usually copper The copper is added to increase the hardness of the metal and to give it a darker color The gold used most in jewelry is 14 or 12 carats fine
Production — The total value of the gold product of the United States during 1912 was $93,451,000 Of this the following states and territories were the largest producers
Alaska $17,198,000 Nevada $13,576,000
California 20,008,000 South Dakota 7,823,000
Colorado 18,741,000 Utah 4,312,000
Of the total product, placers gelded gold valued at $23,019,633, and quaitz veins, metal valued at $62,112,000 The balance of the gold was obtained from ores mined mainly for other metals, and in these it is probably not in the metallic state Moreover, some of the ore in quartz veins is a gold telluride, but by far the greater portion of the product from the quartz veins and placers was furnished by the native metal
The world's yield of the precious metal in 1912 was valued at $466,- 136,100 The principal producing countries and the value of the gold produced by each were
South Africa $211,850,600 Mexico $24,450,000
United States 93,45 1,500 India 11,055,700
Australasia 54,509,400 Canada 12,648,800
Russia 22,199,000 Japan 4,467,000
Lead occurs very rarely as octahedral or dodecahedral crystals, in thin plates and as small nodular masses in districts containing man- ganese and lead ores and also in a few placers It usually contains small quantities of silver and antimony The native metal ha1} the same properties as the commercial metal Its hardness 13 i 5 and density 113 It melts at about 33 5°
The mineral is of no commercial importance The metal is obtained from galena and other lead compounds
Mercury occurs as small liquid globules in veins of cinnabar (HgS) from which it has probably been reduced by organic substances, and ift
Introduction— The Elements 63
the rocks traversed by these veins The native metal possesses the same properties as the commercial metal It solidifies at — 39°, when it crystallizes in octahedrons ha\mg a cubic cleavage Its density is 13 6 Its boiling-point is 350°
The commercial metal is obtained from cinnabar (p 98).
Amalgam (Ag Hg) is found in dodecahedral crystals in a few places, associated with mercury and silver ores It occurs also as embedded grams, m dense masses and as coatings on other minerals It is silver- white and opaque and gives a distinct silver streak when rubbed on copper Its hardness is about 3 and its density 13 9 When heated in the closed tube it yields a sublimate of mercury and a residue of silver On charcoal the mercury volatilizes, leaving a silver globule, soluble in nitric acid
Platinum-Iron Group
The platinum-iron group of minerals may be divided into the plati- num and the iron subgroups The latter composes only iron and nickel- it on, both of which are extremely rare, and the former, the metals platinum, indium, osmium, ruthenium, rhodium, and palladium The platinum metals probably constitute an isodimorphous group since they occur together in alloys, some of which are isometric and others hexagonal (rhombohedral) Platinum is the only member of the group of economic importance.
Platinum (Pt)
Platinum occurs but rarely in crystals It is almost universally found as granular plates associated with gold in the sands of streams and rivers, and rarely as tiny grains or flakes in certain very basic igneous rocks
As found in nature the metal always contains iron, indium, rhodium, palladium and often other metals. A specimen from California yielded:
Pt Au Fe Ir Rh Pd Cu IrOs Sand Total 85 50 80 6 75 i 05 i oo 60 i 40 i 10 2 95 101 15
Though the metal occurs usually in grains and plates, nevertheless its crystals are sometimes found. On them cubic faces are the most prominent ones, though the octahedrons, the dodecahedrons and tetrahexahedrons have also been identified Like the crystals of silver and gold, those of platinum are frequently distorted.
64 Descriptive Mineralogy
The color of platinum is a little more gray than that of silver Its streak is also gray Its hardness is 4-4 5 and density 14 to 19 Pure platinum has a density of 21 5 It is malleable and ductile, a good conductor of electricity, and it is infusible before the blowpipe except in very fine wire It is not dissoh ed by any single acid, though soluble, like gold, in aqua regia Its melting temperature is 1755°
Syntheses —Crystals have been obtained by cooling siliceous mag- mas containing the metal, and by dissolving the metal in saltpelei and cooling the mixture
Occurrence — Platinum is found in the sands of rivers or beaches and in placer deposits in which it occurs in flattened scales or in small grains Nuggets of considerable size are sometimes met with, the largest known weighing about iSf kilos It is present also in small quantity in certain very basic igneous rocks, like pendotite
Localities — It occurs m nearly all auriferous placer districts and in small quantities in the sands of many rivers, among them the Ivalo in Lapland, the Rhine, the rivers of British Columbia, and of the Pacific States It is more abundant in the Natoos Mountains in Borneo, on the east flanks of the Ural Mountains in Siberia, in the placer of an old river in New South Wales, Australia, and the sands of rivers of the Pacific side of Colombia It is nearly always associated with chromite (p 200) A recent discovery which may prove to be of con- siderable importance is near Goodsprmgs, Nev , where platinum is in the free state associated with gold in a siliceous oie
The native metal is probably an original constituent of some pen- dotites (basic igneous rocks) Its presence m placers is due to the disintegration of these rocks by atmospheric agencies
Extraction and Refimng — The metal is separated from the sand with which it is mixed by washing and hand picking The metallic powder is then refined by chemical methods
Uses — On account of its infusibihty and its power to resist the coi- rosion of most chemicals the metal is used extensively for ciuciblcs and other apparatus necessary to the work of the chemist It is also used by dentists and by the manufacturers of incandescent electric lamps It is an important metal in the manufactuie of physical and certain surgical instruments, and was formerly used by Russia for coin- age The most important use of the metal in the industries is in the manufacture of sulphuric acid Sulphur dioxide (SCb) and steam when mixed and passed over the finely divided metal unite and foim HjSOi More than half of the acid made at present as manufactured by this process
Introduction— The Elements
Production — Most of the platinum of the world is obtained from placers in the Urals in Russia A small quantity is washed from the sands of gold placers in Colombia, Oregon and California, and an even smaller quantity is obtained during the refining of copper from the ores of certam mines The total production of the world in 1912 was 314,751 oz The output for Russia m this year was about 300,000 oz , of Colombia about 12,000 oz , and of the United States 721 oz (equiv- alent to 505 02 of the refined metal, valued at $22,750) In addition, about 1,300 oz were obtained m the refining of copper bullion imported from Sudbury, Ont , and m the treatment of concentrates from the New Rambler Mine, Wyoming Of this about 500 oz were produced
pIG 35 — iron Meteorite (Sidente) from Canyon Diablo, Arizona Weight 265 Ibs (Field Columbian Museum )
from domestic ores The importations into the United States for the same year were about 125,000 oz , valued at $4,500,000
Platinum-iron, or iron-platinum (Pt Fe), contains from 10 per cent to 19 per cent Fe It is usually dark gray or black and is magnetic It is found with platinum m sands of the rivers in the Urals Its crystals are isometric
Iron (Fe) occurs in small grains and large masses in the basalt at Ovifak, Disko Island, W Greenland, and at a few other points in Green- land, and alloys consisting mainly of iron are found in the sands of some rivers in New Zealand, Oregon and elsewhere The native metal always contains some nickel The most common occurrence of iron, however, is m meteorites (Fig 25) In these bodies also it is aUoyed with Ni When
Descriptive Mineralogy
polished and treated with nitric acid, surfaces of meteoric iron exhibit penes of lines (Widmanstatten figures), that are the edges of plates of different composition (Fig 26) These are so arranged as to indicate that the substance crystallizes in the isometric system
Iridium (Ir Pt) and platin-iridium (Pt Ir) are alloys of indium and platinum found as silver- white grains with a yellowish tinge, associated with platinum in the sands of rivers in the Urals, Burmah and Brazil Their hardness is 6 to 7, and density 22 7 The mineral is isometric and its fusing point is between 2i5o°-225o°.
FIG 26 — Widmanstatten Figures on Etched Surface of Meteorite from Toluca, Mexico (One-half natural size ) (Field Columbian Mit\ )
Palladium (Pd) is usually alloyed with a little Pb and Ir It is found in small octahedrons and cubes and also in radially fibrous grams in the platinum sands of Brazil, the Urals and a few other places It is whitish steel-gray in color, has a hardness of 4 to 5 and a density of ii 3 to ii 8 It fuses at about 1549° Its crystallization is isometric About 2,390 oz of the metal were produced in the United States during 1912, but all of it was obtained during the refining of bullion. The imports were 4,967 oz , valued at $213,397
Allopalladium (Pd) is probably a dimorph of palladium It is found in six-sided plates that are probably rhombohedral, intimately asso- ciated with gold, at Tilkerode, Harz
Introduction— The Elements 67
Osmiridium (Os Ir) and mdosmine (Ir Os) are foundm crystals and flattened grams and plates that are apparently rhombohedral They consist of Ir and Os m different proportions, often with the addition of rhodium and ruthenium Osmiridium is tin-white and iridosrmne steel-gray Their hardness is 6 to 7 and density 19 to 21 When heated with KNOs and KOH, both yield the distinctive chlorine-like odor of osmium o\ide (Os04) and a green mass, \\hich, when boiled with water, leaves a residue of blue indium oxide Both are insoluble in concentrated aqua regia They occur platinum in the sands of rivers m Colombia, Brazil, California, the Urals, Borneo, New South Wales, and a few other places They are distinguished from platinum by greater hardness, light color and insolubility in strong aqua regia
The world's product of refined indium is about 5,000 oz , of which the United States furnishes about 500 oz Its value is $63 per oz Imports into the United States during 1911 were 3,905 oz, valued at $210,616 The sources of the metal are native indium, osrniridmm, platinum, copper ore and bullion The metal is obtained from the last two sources in the refining process
Chapter Iv
The Sulphides, Tellurides, Selenides, Arsenides And Antimonides
THE sulphides are combinations of the metals, or of elements acting like bases, with sulphur They may all be regarded as derivatives of hydrogen sulphide (H2S) by the replacement of the hydrogen by some metallic element The tellundes are the corresponding compounds of EfeTe, and the selemdes of EkSe
With the same group are also placed the arsenides and the anti- monides, derivatives of HsAs and HsSb, because arsenic and antimony so often replace m part the sulphur of the sulphides, forming with these isomorphous mixtures
The minerals described in this volume may be separated into the following groups and subgroups
I The sulphides, tellundes and selemdes of the metalloids arsenic, antimony, bismuth and molybdenum
II The sulphides, tellundes, selemdes, arsenides and antimonides of the metals
(a) The monosulphides, etc (Derivatives of HsS, HgSe, HsTe,
H3As, H3Sb ) (&) The disulphides, etc (Derivatives of 2HsS, 2H2Te, 2HsAs,
2H3Sb)
All sulphur compounds when mixed with dry sodium carbonate (Na2COs) and heated to fusion on charcoal yield a mass containing sodium sulphide (Na2$) If the mass is removed from the charcoal, placed on a bright piece of silver and moistened with a drop or two of water or hydrochloric acid, the solution formed will stain the silver a dark brown or black color (AgsS), which will not rub off The sulphides yield the sulphur reaction when heated with the carbonate on platinum foil, the sulphates only when charcoal or some other reducing agent is added to the mixture before fusing Moreover, the sulphides yield sulphureted hydrogen when heated with hydrochloric acid, while the sulphates do not. These tests are extremely delicate. By the aid of
Sulphides, Tellurides, Etc 69
the first one the sulphur in any compound may be detected By the aid of the others the sulphates may be distinguished from the sulphides
The selemdes are recognized by the strong odor evolved heated before the blowpipe Selenates and selemtes give their odor only after reduction with Na2COs
The tellundes, wanned with concentrated HoSO-t, dissolve and yield a carmine solution from which water precipitates a black gray powder of tellurium
All substances containing arsenic and antimony yield dense white fumes when heated on charcoal in the oxidizing flame The fumes of arsenic possess a characteristic odor while those of antimony are odorless When heated in the open tube, arsenides and compounds sulphur and arsenic yield a very volatile sublimate composed of tiny white crys- tals (AS203) The corresponding sublimate for antimomdes and for compounds with antimony and sulphur is nonvolatile, or difficultly volatile, and apparently amorphous It is usually found on the under side of the tube
The Sulphides, Selenides And Tellurides Of The Metalloids
The sulphides of the metalloids include compounds of sulphur with arsenic, antimony, bismuth and molybdenum and a selemde and several tellundes of bismuth Only the sulphides are of importance. One, shbmte (Sb2Ss), is utilized as a source of antimony
Realgar (As2S2)
Realgar occurs as a bright red incrustation on other substances, as compact and granular masses and as crystals implanted on other minerals It is usually associated with the bright yellow orpunent
(P 7i)
Absolutely pure realgar should have the following composition
As, 70 i per cent, S, 29 9 per cent The mineral, however, usually contains a small amount of impurities It may be looked upon as a derivative of H2S in which the hydrogen of two molecules is replaced by two arsenic atoms, thus*
H2S As=S
yielding H2S As=S,
Descriptive Mineralogy
oo P 5b , oio (b) , oP, ooi (c), Poo, on (q) and P, in M
Crystals of realgar are usually short and prismatic m habit They are monoclmic (prismatic class) with an axial ratio a b c 44 i . 973 and /3=66° 5' The characteristic prismatic faces are (w)ooP(uo) and (J)ooP2(2io) These with (b) oo P 5b (oio) con- stitute the prismatic zone The terminations are (r) 00(012) or (q) Pob (on) in combination with the basal plane (0 oP(ooi), the orthodome (a) (Toi), and one or more of several pyramids (See Fig 27 ) The crystals are usually small and are striated vertically Prismatic angle 1 10 A ilo
105° 34'
The mineral possesses a distinct cleavage parallel to (fc)ooPoo and (/) oo P5 It is sectile, soft (H= i 5-2), resinous in luster and aurora-red or orange in color Its streak is a lighter shade, but with the mineral are fre- quently intermingled small quantities of orpi- FIG 27 — Realgar Crystal ment which impart to its streak a distinct yellow tinge Its density is 3 56 In thin splinters it is often translucent or trans- parent, and strongly pleochroic m red and yellow tints, but in masses it is opaque Its indices of refraction are not known with accuracy, but its double re- fraction is strong ( 030) It is a nonconductor of electricity
When heated on charcoal before the blowpipe realgar catches fire and burns with a light blue flame, at the same time giving off dense clouds of arsenic fumes and the odor of burning sulphur (SOs) When heated in a closed tube it melts, volatilizes and yields a transparent red sublimate in the cold parts of the tube
Its bright red color and its reaction for sulphur distinguish realgar from all other minerals but cinnalar, the sulphide of mercury (p 9#) It may easily be distinguished from cinnabar by its softness, its low specific gravity and the arsenic fumes which it yields when heated on charcoal
On exposure to the air and to light realgar oxidizes, yielding orpi- ment (As2Ss) and arsenolite (As20s)
Syntheses —Realgar is often produced in the flues of furnaces m which ores containing sulphur and arsenic are roasted Crystals have also been produced by heating to 150° a mixture of AsS with an excess of sulphur in a solution of bicarbonate of soda sealed m a glass tube
Occurrence Localities and Origin — Realgar occurs in masses asso dated with orpiment and m grams scattered through it at all places
Sulphides, Tellurides, Etc 71
where the latter mineral is found It also occurs associated with silver and lead ores in many places It is found in crystals implanted on quartz and on the walls of cavities in lavas It "is also occasionally a deposit from hot springs In the United States it forms seams in a sandy clay in Iron Co , Utah Its crystals are found in calcite in San Bernardino and Trinity Counties, California, and with orpiment it is deposited as a powder by the hot water of the Norns Geyser basin in the Yellowstone National Park
In most cases it is a product of the interaction of arsenic and sul- phur vapors.
Uses — The native realgar occurs in too small a quantity to be of commercial importance An artificial realgar is employed in tanning and m the manufacture of " white-fire "
Orpiment (As2S3)
Orpiment, though more abundant than realgar, is not a common mineral It is usually found m foliated or columnar masses with a. bright yellow color Its name — a contraction from the Latin aun- pigmentum, meaning golden paint — refers to this color
The pure mineral contains 39 per cent of sulphur and 61 per cent of arsenic, corresponding to the formula As2Sa It thus contains about 9 per cent more sulphur than does realgar.
The monoclmic orpiment crystals have the symmetry of the pris- matic class Their axial ratio is 596 . i 665 with £=89° 19' Though always small they are distinctly prismatic with an orthorhombic habit Their predominant faces are the ortho and clino pmacoids, several prisms and the orthodome
The cleavage of orpiment is so perfect parallel to °o P ob (oio) that even from large masses of the mineral distinct foliae may be split These are flexible but not elastic The mineral, like many other flexible minerals, is sectile Its luster is pearly on cleavage faces, which are always vertically striated, and is resinous on other surfaces The color of pure orpiment is lemon-yellow, it shades into orange when the mineral is impure through the admixture of realgar Its streak is always of some lighter shade than that of the mineral Its hardness is i 5-2 and its density about 34 In small pieces orpiment is translucent and possesses an orange and greenish yellow pleochroism When heated to 100° it becomes red and assumes the pleochroism of realgar. It, however, resumes its characteristic color and pleochroism upon cooling. When heated to 150° the change is permanent. The mineral is a nonconductor of electricity.
72 Descriptive Mineralogy
The chemical properties of orpiment are the same as those described for realgar, except that the sublimate in the closed tube is yellow instead of red
Synthesis —Orpiment is produced in large plcochroic crystals by treatment of arsenic acid with H2S under high prcssuie
Occurrence, Localities and Origin —Orpiment occurs in the same forms and in the same places as does realgar Small specks of it occur on arsenical iron at Edenville, NY It is also found in the deposits of Steamboat Springs Nevada The origin of orpiment is similar to that of realgar It is also formed by the oxidation of this mineral
Uses —Native orpiment mixed with water and slaked lime is used in the East as a wash for removing hair It is also employed as a pig- ment in dyeing Most of the As2§3 of commerce is a manufactured product
Stibnite Group (R>Q3)
The stibmte group of sulphides contains several isomorphous compounds, of which we shall consider only two, viz , Uibmtc and Usmuthimte (61283) The general formula of the group is m which R stands for Sb or Bi and Q for S 01 Se The gioup is orthorhombic (bipyramidal class) All the members have a distinct cleavage parallel to the brachypmacoid which yields flexible laminae
Sfobnite (Sb2Sa)
Stibmte is the commonest and the most important ore of anti- mony It is found in acicular and prismatic crys- tals, in radiating groups of crystals and m fibrous masses
Chemically, stibmte is the antimony tnsul- phide, SboSa, composed of SI), 71 4 per cent and S, 28 6 per cent Ab found, however, it usually contains small quantities of iron and often traces of silver and gold
„ „ „ , Crystals of stibmte are often very comnh-
FIG 28 —Stibmte Crys- , , 11, i .
tal M p no (w) caec They are orthorhombic with an axial ratio
OOP So, oio (ft), 2P2 9926 i 10179 and a columnar or acicular 121 00 and P, iii(.p) habit The most important forms m the pris- matic zone are oo P(no) and oo P 56 (oio). The prisms are often acutely terminated by P(iu), 4(431) and 6P2(36i), or bluntly terminated by iP(ii3), (Fig 28) Sometimes the crystals are rendered very complicated by the great number of their terminal
Sulphides, Tellurides, Etc. 73
planes Dana figures a crystal from Japan that possesses a termina- tion of 84 planes no A ilo=89° 34'
Many of the crystals of this mineral, more particularly those with an acicular habit, are curved, bent or twisted Nearly "all, whether curved or straight, are longitudinally striated
The cleavage of stibmte is very perfect parallel to oo P 06 (oio), leaving striated surfaces The mineral is soft (H=2) and slightly sectile Its density is about 4 5 Its color is lead-gray and its streak a little darker In very thin splinters it is translucent in red or yellow tints In these the indices of refraction for yellow light have been determined to be, 0=4303 and 7=3 194 Surfaces that are exposed to the air are often coated with a black or an iridescent tarnish The luster of the mineral is metallic It is a nonconductor of electricity
Stibmte fuses very easily, thin splinters being melted even in the flame of a candle When heated on charcoal the mineral yields anti- mony and sulphurous fumes, the former of which coat the charcoal white in the vicinity of the assay When heated in the open tube SCb is evolved and a white sublimate of Sb20s is deposited on the cool walls of the tube In the closed tube the mineral gives a faint ring of sulphur and a red coating of antimony oxysulphide It is soluble in nitric acid with the precipitation of Sb20s
Stibmte may easily be distinguished from all minerals but the other sulphides by the test for sulphur From the other sulphides it is dis- tinguished by its cleavage and the fumes it yields when heated on char- coal Its closest resemblance is with galena (PbS), which, however, differs from it in being less fusible and in yielding a lead globule when fused with sodium carbonate on charcoal. Moreover, galena possesses a cubic cleavage
Syntheses — Stibnite is produced by heating to 200°, a mixture of sulphur and antimony with water under pressure, and by the reaction of H2S on antimony oxide heated to redness
Occurrence, Localities and Origin — The mineral is found as crystals in quartz veins cutting crystalline rocks, and in metalliferous veins asso- ciated with lead and zinc ores, with cinnabar (HgS) and barite (BaSO-i) The finest crystals, some of them 20 inches in length, come from mines in the Province of lyo, on the Island of Shikoku/Japan The mineral occurs also m York Co , New Brunswick, in Rawdon township, Nova Scotia, at many points in the eastern United States, in Sevier Co , Arkansas, in Garfield Co , Utah, and at many of the mining districts in the Rocky Mountain States
In Arkansas stibmte is in quartz veins following the bedding planes
74 Descriptive Mineralogy
of shales and sandstones With it are found many lead, zmc and iron compounds and small quantities of rarer substances In Utah the mineral occurs m veins unmixed AMth other minerals, except its oxidation products The veins follow the bedding of sandstones and conglomerates Here, as in Arkansas, the stibnite is believed to have been deposited by magmatic waters
Uses —Stibnite was powdered by the ancients and used to color the eyebrows, eyelashes and hair At present it is used to a slight extent in vulcanizing rubber and in the manufacture of safety matches, percussion caps, certain kinds of fireworks, etc Its principal value is as an ore of antimony Practically all of the metal used in the arts is obtained from this source Antimony is chiefly valuable as an alloy with other metals With tin and lead it forms type metal The principal alloys with tin are britannia metal and pewter With lead, tin and copper it constitutes babbit metal, a hard alloy used in the construction of locomotive and car journals, and with other substances it enters into the composition of other alloys used for a variety of purposes The double tartrate of antimony and potassium is the well known tartar emetic. The pigment, Naples yellow, is an antimony chromate.
Production — The total quantity of stibnite mined in the world can- not be accurately estimated That mined in the United States is very small in amount, most of the antimony produced m this country being obtained in the form of an antimony alloy as a by-product in the smelting of antunomal lead ores
Bismuthinite (Bi2S3)
Bismuthimte is completely isomorphous with stibnite It rarely, however, occurs in acicular crystals, but is more frequently in foliated, fibrous or dense masses
Its axial ratio is 968 i : 985.
The angle noAiTo 88° 8'
The mineral resembles stibnite in color and streak, but its surface is often covered with a yellowish iridescent tarnish Its fusibility and hardness are the same as those of stibnite but its density is 6 8-7 i It is an electrical conductor
In the open tube the mineral yields S02 and a white sublimate which melts into drops that are brown while hot, but change to opaque yellow when cold On charcoal it yields a coating of yellow 81203 which changes to a bright red Bils when moistened with potassium iodide The mineral dissolves in hot nitric acid, forming a solution, which upon the addition of water gives a white precipitate of a basic bismuth nitrate.
Sulphides, Tellurides, Etc ?5
Bismuthmite is distinguished from stibmte by the coating on char- coal and by its complete solubility in HNOa
Syntheses — Crystals have been obtained by cooling a solution of m molten bismuth, and by cooling a solu.ion made by heating BioSs m a solution of potassium sulphide in a closed tube at 200°.
Occurrence , Localities and Origin — Bismuthmite occurs as a constit- uent of veins associated \vith quartz, bismuth and chalcopynte, in which it was probably formed as a product of pneumatolytic processes It is found at Schneeberg and other points in Saxony, at Redruth and elsewhere in Cornwall, near Beaver City, Utah, in a gold-bearing veiii at Gold Hill, Rowan County, N C , and in a vein containing benl, garnet, etc , in granite at Haddam, Conn
Tetradymite Group
This group comprises a series of tellundes and selemdes of bismuth that have not been satisfactorily differentiated because of the lack of accurate analyses
Tetradymite, the best known member of the group, is probably an isomorphous mixture cf bismuth tellunde and bismuth sulphide of the formula Bi2(Te 8)3 It occurs in small rhombohedral cnstals with the axial ratio i . i 587 and loli A 1101 98° 58' Its crystals are bounded by rhombohedrons (R(ioTi) and 2R(202ii)) and the basal plane (oP(oooi)). Interpenetration fourlings are common with — |R(oil2), the twinning plane The mineral is, however, more frequently found in foliated and granular masses. Its color is lead-gray It possesses a perfect cleavage parallel to the base Its hardness is i 5-2 and its density about 74 It is a good electncal conductor Its best known occurrences are Zsubkau, Hungary, Whitehall, Va, in Davidson County, N C , near Dahlonega, Ga , near Highland, Mont , and at the Montgomery Mine and at Bradshaw City in Arizona It occurs in quartz veins associated with gold in the gold sands of some streams
The other members of the group appear to be completely isomorphous with tetradymite. They vary m color from tin-white through gray to black.
Molybdenite (MoS)
This mineral, which is the sulphide of the rare metal molybdenum, does not occur in large quantity, but it is so widely distributed that it seems to be quite abundant It occurs principally in black scales scat-
76 Descriptive Mineralogy
tered through coarse-grained, crystalline, siliceous rocks and granular limestones and in black or lead-gray foliated masses
The theoretical composition of molybdenite is 40 per cent sulphur and 60 per cent molybdenum Usually, however, the mineral contains small quantities of iron and occasionally other components
Crystals of molybdenite are exceedingly rare Scales and plates with hexagonal outlines are often met with but they do not usually pos- sess sufficiently perfect faces to >ield accurate measurements The measurements that have been obtained appear to indicate a holohedral hexagonal symmetry with an axial ratio i i 908
The cleavage of molybdenite is very perfect parallel to the base. The laminae are flexible but not elastic The mineral is sectile and so soft that it leaves a black mark when drawn across paper Its density is 4 7. Its luster is metallic, color lead-black, and streak greenish black In very thm flakes the mineral is translucent with a green tinge Otherwise it is opaque It is a poor conductor of electricity at ordi- nary temperature, but its conductivity increases with the temperature
In the blowpipe flame molybdenite is infusible It, however, im- parts to the edges of the flame a yellowish green color Naturally, it yields all the reactions for sulphur, and in the open tube it deposits a pale yellow crystalline sublimate of MoOs Molybdenite is decomposed by nitric acid with the production of a gray powder (MoOs)
By its color, luster and softness molybdenite is easily distinguished from all minerals but graphite From this it is distinguished by its reaction for sulphur Moreover, a characteristic test foi all molyb- denum compounds is the dark blue coating produced on porcelain when the pulverized substance is moistened with concentrated sulphuric acid and then heated until almost dry Before this test can be applied to molybdenite, the mineral must first be powdered and then oxi- dized by roasting in the air for a few minutes or by boiling to dryness with a few drops of HNOs
Syntheses —Crystalline molybdenite has been prepared by the action of sulphur vapor or EfeS upon glowing molybdic acid It has also been produced by heating a mixture of molybdates and lime, in a large excess of a gaseous mixture of HC1 and EfeS.
Occurrence, Localities arid Origin — Molybdenite generally occurs embedded as grams in limestone and in the crystalline silicate rocks, as, for instance, granite and gneiss, and as masses in quartz veins, at Arendal, Norway, at Blue Hill Bay, Maine, at Haddam, Conn , m Renfrew Co , Ontario, and at many points in the far western states It is thought to be of pneumatolytic origin.
Sulphides, Tellurides, Etc 77
Uses — The mineral is the principal ore of the metal molybdenum, the salts of which are important chemicals employed principally in analytical work, especially in the detection and estimation of phosphoric acid The molbdate of ammonia (NHMoO the principal salt employed in analytical processes, is easily obtained by roasting a mix- ture of sand and molybdenite and treating the oxidized product with ammonia Other molybdenum salts are used for giving a green color to porcelain The metal is used in an alloy (ferro-mol}bdenum) for hardening steel, as supports for the lower ends of tungsten filaments in electric lamps and for making ribbons used in electric furnaces
Production — There was no production of molybdenite in North America during 1912 The imports of the metal into the United States aggregated 3 5 tons, valued at $4,670. The value of the imports of the ore is not known*
THE SULPHIDES, SELEWIDES, ETC., OF THE METALS THE METALLIC MONOSULPHIDES, ETC
The metallic monosulphides, monoselemdes, etc , are compounds in which the hydrogen of H2S, H2Se, H2Te, HsAs, and HsSb are replaced by metals Among them are some of the most important ores
They may be separated into several groups of which some are among the best defined of all the mineral groups, while others consist simply of a number of minerals placed together solely for convenience of description In addition, there are a few members of this chemical group which seem to have no close relationship with any other mem- bers These are discussed separately
The groups described are as follows:
The Dyskrasite Group The Galena Group The Chalcocite Group. The Blende Group The Millerite Group The Cinnabar Group.
DYSKRASITE GROtJP
This group includes a number of arsenides and antimonides, some of which apparently contain an excess of the metal above that neces- sary to satisfy the formulas HsAs and HsSb. Although their com-
78 Descriptive Mineralogy
position is not understood, they are generally regarded as basic com- pounds A few of them are well crystallized, but their composition is doubtful, because of the difficulty of obtaining pure material for anal- yses Some of them are probably mixtures The members of the group, all of which are ccmparatrvely rare, are wkitneyite (CuoAs), algodomte (CueAs), domeykite (CuaAs), horsfordite (CuSb) and dyskras- ite (AgaSb) Other minerals are known which may properly be placed here, but their identity is doubtful The only two members that need further discussion are domeykite and dyskrasite
Domeykite (CuaAs) is known only in disseminated particles and in botryoidal and dense masses and small orthorhombic crystals It may be a mixture of several components, which in other proportions form algodomte It is tin-white or steel-gray and opaque It becomes dull and covered with a yellow or brown iridescent tarnish when ex- posed to the air Its hardness is 3-4 and density about 73 It is the most easily fusible of the copper arsenides Its principal occurrences are m the silver mines of Copiapo and Coquimbo in Chile, associated T\ith native copper at Cerro de Paracabas, Guerrero, Mexico, at Shel- don, Portage Lake, Michigan, and on Michipicoten Island, in Lake Superior, Ontario The last two occurrences are in quartz veins
Dyskrasite (AgaSb) occurs in foliated, granular and structureless masses and rarely in small orthorhombic crystals with an hexagonal habit Their axial ratio is 5775 i . 6718, Twinning is frequent, yielding star-shaped aggregates The mineral has a silver-white color and streak, but its exposed surfaces are often tarnished yellow or bUck It is opaque and sectile Its hardness is 3 5-4 and density about 9 6 It is a good electrical conductor Dyskrasite is soluble in HNO leaving a white sediment of Sb20s It occurs principally in the silver mines of central Europe, and especially near Wolfach, Baden, St Andreasberg, Harz, and at Carnzo, in Copiapo, Chile.
Galena Group
The minerals comprising the galena group number about a dozen crystallizing m the holohedral division of the regular system (hex- octahedral class) They possess the general formula RQ in which R represents silver, lead, copper and gold, and Q sulphur, selenium and tellurium The group may be divided into silver compounds and lead compounds, thus (A) argentite (Ag2S), hessite (Ag2Te), petzite ((Ag Au)2Te), naumanmte (Ag2Se), agmlante (Ag2(Se S)), jalpaitc
Sulphides, Tellurides, Etc 79
((Ag Cu)2S) and eukante ((Ag Cu)2Se), and (B) galena (PbS\ altaite (PbTe), and dausttalite (PbSe) Of these onh two are of importance, viz, galena, and argentite Hessite and petzite are comparative!} unimportant ores of gold
Argentite (AgoS)
Argentite, though not very widespread m its occurrence, is an important ore of silver It is found in masses, as coatings, and in crys- tals or arborescent groups of crystals
Argentite contains 87 i per cent silver and 12 9 per cent sulphur when pure It is usually, however, impure through the admixture of small quantities of Fe, Pb, Cu, etc
The forms most frequently observed on argentite crystals are ooOoo(ioo), ooO(no) and 0(in), though various wOoo (hid) and wOm (hll) forms are also met Tvith The crystals are often distorted and often they are grouped in paiallel growths of different shapes Twinning is common, with 0(in) the twinning plane The twins are usually penetration twins The habit of most crystals is cubical or octahedral
Argentite is lead-gray in color Its streak is a little darker The mineral is opaque Its luster is metallic, its hardness about 2 25 and* density 73 It is sectile, has an imperfect cleavage and is a conductor of electricity
When heated on charcoal argentite shells and fuses, yielding sulphur fumes and a globule of silver It is soluble m nitric acid
Argentite is easily recognized by its color, its sectility, the fact that it yields a silver globule when fused with Na2COs on charcoal and yields the sulphur test with a silver corn
Syntheses — Crystals of argentite may be obtained by treating red hot silver with sulphur vapor or dry HfcS, and by heating silver and SCb in a closed tube at 200°
Occurrence, Localities and Origin — The mineral is found in the second- ary enrichment zones of veins associated with silver and other sulphides in many silver-mining districts In Nevada it is an important ore at the Comstock lode and in the Cortez district It is found also near Port Arthur on the north shore of Lake Superior, in Ontario, and asso- ciated with native silver in the copper mines of Michigan The ores of Mexico, Chile, Bolivia and Peru are composed largely of this mineral.
Production — Much of the silver produced in this country is obtained from argentite, though by no means so great a quantity as is obtained from other sources*
80 Descriptive Mineralogy
Hessite (Ag2Te) and Petzite ((Ag Au)2Te)
These two minerals, though comparatively rare, are prominent sources of gold and silver in some mining camps They usually occur together associated with other sulphides.
Hessite is the nearly pure silver tellunde and petzittf, &n isomorphous mixture of gold and silver tellundes, as indicated by the following analy- ses of materials from the Red Cloud Mine, Boulder Co , Colorado
Te
Ag
Au Cu
Pb Fe
Zn
Si02
Total
22 17
45 i 35
13 09 °7
17 36
Is
The minerals crystallize in all respects like argentite They are opaque and lead-gray to iron-black in color, sectile to brittle, have a hardness between 2 and 3 and a specific gravity of 8 3-9, increasing with the percentage of gold present They are good conductors of electricity
Before the blowpipe, both minerals melt easily to a black globule, at the same time coloring the reducing flame greenish and giving the odor of tellurium fumes When acted upon by the reducing flame, the globule becomes covered with little crystals of silver With Na2COs on charcoal both minerals yield a globule of silver, but the globule obtained from hessite dissolves in warm HNOs, while that obtained from petzite becomes yellow (gold) In the open tube both yield a white sublimate of TeO2 which melts, when heated, to colorless drops When heated with concentrated HSCU, they give a purple or red solution which, upon the addition of water, loses its color and precipitates blackish gray, powdery tellurium. The minerals dissolve in HNOs From this solu- tion HC1 throws down white silver chloride
Both the minerals resemble very closely many forms of argentite and galena, from which, however, they may be distinguished by the reactions for tellurium Petzite and hessite may be distinguished from one another by the test for gold Moreover a fresh surface of hessite blackens when treated with a solution of KCN, whereas a surface of petzite remains unaffected
Syntheses —Octahedrons of hessite are obtained by the action of tellurium vapor upon glowing silver in an atmosphere of nitrogen, and dodecahedrons of petzite upon similar treatment of gold-silver alloy
Origin — Both minerals are believed to be primary deposits orig- inating in magmatic solutions They occur in veins with native gold, quartz, fluonte, dolomite, and various sulphides and other tellundes.
Sulphides, Tellurides, Etc 81
Localities —These tellundes, together uith others to be described later (p 113), are important sources of silver and gold in the mines at Nagyag, Transylvania, at Cripple Creek and in Boulder Co , Colo , and at Kalgoorhe, W Australia The quantity of tellundes mined is con- siderable, but since it is impracticable to separate these tellundes from the other compounds of gold and silver mined with them, it is im- possible to estimate the proportion of the metals obtained from them
Galena (PbS)
Galena, the most important ore of lead, occurs in great lead-gray crystalline masses, in large and small crystals, in coarse and fine granukr aggregates, and in other less common forms Much galena contains silver, m which case it becomes an important ore of this metal
Galena rarely approaches the theoretical composition 13 4 per cent cf sulphur and 86 6 per cent of lead It usually contains small quanti- ties of the sulphides cf silver, zinc, cadmium, copper and bismuth and in some cases native silver and gold When the percentage of silver present reaches 3 oz per ton the mineral is ranked as a silver ore This silver is apparently present in some cases as an isomorphous mixture of silver sulphide and m other cases in distinct minerals included within the galena
Galena crystals usually possess a cubical habit, though crystals with the octahedral habit are very common The principal forms observed are
ooOoo(ioo), 0(in), ooO(no), mQoo(klo) and
mQm (hlT) (Figs 29 and 30) Twins are common, 0 the twinning face FlG 29 -Galena ays-
Galena is well characterized by its lead-gray °°' J,°? color, its perfect cleavage parallel to the cubic faces an Q, ni (o) and by its great density (8 5) Its luster is me- tallic and its hardness about 2 6 Its streak is grayish black. It is a good conductor of electricity
On charcoal galena fuses, yielding sulphurous fumes and a globule of metallic lead, which may easily be distinguished from a silver globule by its softness The charcoal around the assay is coated with a yellow sublimate of lead oxide (PbO) The mineral is soluble in HNOs with the separation of sulphur
Its color and luster distinguish galena from nearly all minerals but s Unite From this mineral it is easily distinguished by its more difficult fusibility, by its cleavage, and by the fact that it does not yield the anti- mony fumes when heated on charcoal
Descriptive Mineralogy
Galena weathers readily to the sulphate (anglesite) and carbonate (cerussite) , consequently it is usually not found m the upper portions of veins that are exposed to the action of the air.
Syntheses —Crystals of galena result from heating a mixture of lead oxide with NEUCl and sulphur, and from treatment of a lead salt with HgS at a red heat Small crystals have been produced by heating
FIG 30 — Galena Crystals (<*>OQ°(IOO) and O(in)) partly covered by Manasitc, from the Joplm District, Mo (After UT 6 T Smith and C I1 bitbentlial )
in a sealed glass tube at 8o°-9o° pulverized cerussite (PbCO,j) in a water solution of HkS
Origin — Veins of galena containing silver (silver-lead) were probably produced by ascending solutions emanating from bodies of igneous rocks, while the galena in limestone was probably deposited by ground- water that dissolved the sulphide from the surrounding sedimentary rocks Galena is also in some cases a metamorphic product
Occurrence — The mineral occurs very widely spread It is found in veins associated with quartz (SiCfe), calcite (CaCOa), bante (BaSOi) or fluonte (CaF2) and various sulphides, especially the zinc sulphide, sphalerite, in irregular masses filling clefts and cavities in limestone,
Sulphides, Tellurides, Etc 83
in beds, and in stalactites and other forms characteristic of water deposits
It occurs also as pseudomorphs after pyromorphite— the lead phos- phate The form that occurs in veins is often silver bearing, while that in limestone is usually free from silver
Localities — Galena is mined m Cornwall and in Derbyshire, Eng- land, in the Moresnet district, Belgium, at various places in Silesia, Bohemia, Spam and Australia In the United States it occurs in veins at Lubec, Me , at Rossie, St Lawrence Co , N Y , at PhoenL\ville, Penn , at Austin's Mines in Wythe Co , Va , and at many other places It is mined for silver in Mexico, at Leadville, Colo , at various points in Montana, in the Cceur d'Alene region in Idaho and at many other places in the Rocky Mountain region
The most extensive galena deposits in this country are in Missouri, m the corner made by the states of Wisconsin, Illinois and Iowa, and in Cherokee Co , Kansas In these districts the galena, associated with sphalerite (ZnS), pynte (FeS2), smithsomte (ZnCOs), calamine ((ZnOH)2SiO3), cerussite (PbC03), calcite (CaCOa) and other minerals, fills cavities in limestone
Extraction of Lead and Silver from Galena — The ore is first crushed and concentrated by mechanical or electrostatic methods, and the concentrates are roasted to convert them into oxides and sulphates The mass is then heated without access of air, sulphur dioxide being driven off, leaving metallic lead carrying impurities, or a mixture of lead and silver
The processes employed in refining the impure lead vary with the nature of the impurities
Uses — Galena is employed to some extent in glazing common stoneware It is also used in the preparation of white lead and other pigments As has alrercly been stated, it is the most important ore of lead and a very important ore of silver
The metal lead finds many uses in the arts Its most common use is for piping Its alloys, type metal, pewter and babbitt metal have already been referred to (p 74) Solder is an alloy of tin and lead, Wood's metal a mixture of lead, bismuth, tin and cadmium The spe- cial characteristic of Wood's alloy is its low fusion point (70°)
Production —The total production of galena by the different coun- tries of the world cannot be given, but the world's production of lead in 1912 was 1,277,002 short tons The total quantity of lead pro- duced by the United States from domestic ores in the same year was about 415,395 tons, valued at $37,385>55° M°st of this was obtained
84 Descriptive Mineralogy
from galena About 171,037 tons were soft lead, smelted from ores mined mainly for their lead and zinc contents, and the balance from ores mined partly for their silver The importance of galena as an ore of silver may be appreciated from the fact that of the $39,197,000 worth of this metal produced in the United States during 1912, silver to the value of about $12,000,000 was obtained from lead ores or from mixtures of lead and zinc ores
Altaite (PbTe) and clausthalite (PbSe) both resemble galena m appearance Both occur commonly in fine-grained masses, but they are also found in cubic crystals Altaite is tin-white, tarnishing to yellow or bronze, and clausthahte is lead-gray Their hardness is 2 5-3 and specific gravity about 8 i They are associated with silver and lead compounds principally in the silver mines of Europe and South America Altaite is known also from several mines in California, Colorado and North Carolina They are distinguished from one another and from galena by the tests for Te and Se
Chalcocite Group
The chalcocite group includes four or five cuprous and argentous sulphides, selemdes and tellundes They all crystallize in the ortho- rhombic system (rhombic bipyramidal class) often with an hexagonal habit, and are isomorphous The best known members of the group are chalcocte (Cu2S) and stromeyente (Cu AgJgS, but only the first- named is common Although these minerals are orthorhombic, never- theless Cu2S is known to exist also in isometric crystals, in which form it is isomorphous with argentite Moreover, stromeyente is an iso- morphous mixture of Ag2$ and Cu2S Therefore, it is inferred that and AggS are isomorphous dimorphs
Chalcocite (Cu2S)
Chalcocite (Cu2S), the cuprous sulphide, is an important ore of copper though by no means as widely spread as the iron-copper sul- phide, chalcopyrite It is usually found in black masses with a dull metallic luster and as a black powder, though frequently also in crys- tals It is a common constituent of the enrichment zone of many veins of copper ores,
The best analyses of chalcocite agree closely with the formula given above, requiring the presence of 20 2 per cent of sulphur and 79 8 per cent of copper Iron and silver are often present in the mineral in small quantity
Sulphides, Tellurides, Etc 85
In crystallization chalcocite is orthorhombic (rhombic bipyramidal class) with the axial ratio 5822 . i 9701 Its crystals contain as their predominant forms oP(ooi), ooP(no), ooP 00(010), P(in),
a series of prisms of the general symbol -P(iiA). and several bra-
m
chydomes Many cf the crystals are elongated parallel to #, and others are so developed as to possess an hexagonal habit (Fig 31) Twins are common according to several laws When the twinning plane is (112) the twins are usually cruciform (Fig 32) The zone ooi— oio is often striated through oscillatory combinations iioAiib=6o° 25' The cleavage of chalcocite is indistinct, its fracture is conchoidal Its hardness is 2 5-3 and density about 5 7. Its streak, like its color,
Fig 31 Fig 32
FIG 31 — Chalcocite Crystal oP, ooi (c), p So , oio (ft), °o P, no (m), 2? £ ,
021 (d), w, 023 (<0, P, iii (p) and JP, 113 00
FIG 32 — Complex Chalcocite Twin, with °o P, no (m) and |P, 112 (p) the Twinning
Planes
is nearly black, but exposed surfaces are often tarnished blue or green, probably through the production of thin films of other sulphides like covellite (CuS), chalcopynte (FeCuSa), etc The mineral is an excel- lent conductor of electricity
In the open tube or on charcoal chalcocite melts and yields sul- phurous fumes
When mixed with Na2COs and heated a copper globule is produced. The mineral dissolves in nitric acid with the production of a solution that yields the test for copper.
Upon exposure to the air chalcocite changes readily to the oxide, cupnte (CusO), and the carbonates, malachite and azurite. In the presence of siliaous solutions it may give rise to the silicate, chrysocolla
(P 44i) .
A pseudomorph of chalcocite after galena is known as Aomnfe.
86 Descriptive Mineralogy
It occurs at the Canton Mine m Georgia and in the Polk Co copper mines in Tennessee Pseudomorphs after many other copper min- erals are common
Chalcocite is recognized by its color and crystallization Massive varieties are distinguished from argentite by greater bnttleness and the reaction for copper, from bormte (CusFeSs) by the fact that it is not magnetic after roasting
Syntheses — Crystals of chalcocite have been made in many ways, more particularly by heating the vapors of CuCb and HS, and by gently warming CuaO in BS Measurable crystals have been observed on old bronze that has been immersed m the waters of hot springs for a long time
Occurrence , Localities and Origin —The mineral is a common prod- uct of the alteration of other copper compounds in the zone of secondary enrichment of sulphide veins. It is therefore present at most localities of copper minerals One of the best known occurrences is Butte, Mont
Fine crystals of chalcocite occur in veins and beds at Redruth and at other places m Cornwall, England, at Bristol m Connecticut, and at Joachunthal in Bohemia The massive variety is known at many places In the United States it occurs m red sandstone at Cheshire in Connecticut It is found also in large quantities near Butte City in Montana, and in Washoe and other counties in Nevada, and indeed in the veins of most copper producing mines In Canada it is present with chalcopynte and bormte at Acton, Quebec, and at several places in Ontario north of Lake Superior
Extraction of Copper — Chalcocite rarely occurs alone in large quantity. In ores it is usually mixed with other compounds of copper, and is treated with them in extracting the metal (see p. 133).
Stromeyerite ((Ag Cu)2S) is usually massive, but it occurs also in simple and twinned crystals similar to those of chalcocite Their axial ratio is 5822 i : 9668, almost identical with that of chalcocite The mineral is opaque and metallic Its color and streak are dark steel- gray Its hardness is 2 5-3 and density about 62 It is soluble m nitric acid It occurs associated with other sulphides in the ores of silver and copper mines at Schlangenberg, Altai, Kupferberg, Silesia, Coquimbo, Copiap6, and other places in Chile, and in a few mines m California, Arizona, and Colorado,
Sulphides, Tellurides, Etc 87
Blende Group
The blende group of minerals comprises a series of compounds whose general formula like that of the galena group is RQ In the blendes R stands for Zn, Cd, Mn, Ni and Fe and Q for S, Se and Te
The blendes are ail transparent or translucent minerals of a lighter color than galena They constitute an isodimorphous group of a dozen or more members crystallizing in the tetrahedral division of the regular system (hextetrahedral class), and in hemimorphic holohedral forms of the hexagonal system (dmexagonal-pyramidal class) The group may be divided into two subgroups known respectively as the sphalerite and the wurtzite groups
Sphalerite Division
The most important member of this division of the blende group is the mineral sphalerite. This, like the other less well known members, crystallizes in the hemihedral division of the regular system with various tetrahedrons as prominent forms The other members of the group are alabandite (MnS), and an isomorphous mixture of FeS and NiS, pentlandite
Sphalerite (ZnS)
Sphalerite, one of the very important zinc ores and one of the most interesting minerals from a crystallographic standpoint, occurs in amor- phous and crystalline masses and in handsome crystals and crystal groups Botryoidal and other imitative masses are common
Pure white sphalerite consists of 67 per cent of Zn and 23 per cent of sulphur The colored varieties usually contain traces of silver, iron, cadmium, manganese and other metals Sometimes the proportion of the impurities is so large that the mineral containing them is regarded as a distinct variety Two analyses of American sphalerites are as follows
S Zn Cd Fe Total
Franklin Furnace, N J 32 22 67 46 tr 99 68
Jophn, Mo 32 93 66 69 42 100 04
The hemihedral condition of sphalerite is shown in the predominance of tetrahedrons among its crystal forms and by the symmetry of its
etched figures (Fig. 33). Its most common forms are — ~(321) and other hextetrahedrons, ±—(221), -(331) and other deltoid-dodeca-
Descriptive Mineralogy
hedrons and ±303(311) and other tristetrahedrons In addition, ooO<(ioo) and ooO(no) are quite common (Fig 34) Twins are abundant Their twinning plane is 0 and their composition face either 0 (Fig 35), or a plane perpendicular to this Through twinning, the crystals often assume a rhombohedral habit
The cleavage of sphalerite is perfect pardlel to ooO(no) From a compact mass of the mineral a fairly good dodecahedron may some- times be split Its fracture is conchoidal When pure the mineral is transparent and colorless As usually found, however, it is yellow, translucent and black, brown, or some shade of red Its streak is brownish, yellow or white. The yellow masses look very much like
Fig 33
Fig 34
Fig 35
FIG 33 — Tetrahedral Crystal of Sphalerite Bounded by oo 0 °o (101) and ±O (in and ill), Illustrating the Fact that Its Octahedral Faces Fall into Two Groups
FIG 34 —Sphalerite Crystal oo 0, no and-f —-, 311 (m) FIG 35 — Sphalente Octahedron Twinned about 0(ni)
lumps of rosin. The hardness of sphalerite is between 3 5 and 4, and its density about 4 Its luster is resinous The minei al is difficultly fusible, and is a nonconductor of electricity Its index of refraction (ri) for yellow light is 2 369.
Sphalerite when powdered always yields tests for sulphur under proper treatment On charcoal it volatilizes slowly, coating the coal with a yellow sublimate when hot, turning white on cooling When moistened with a dilute solution of cobalt nitrate and heated m the reducing flame, the white coating of ZnO turns green The mineral dis- solves in hydrochloric acid, yielding sulphuretted hydrogen
By oxidation sphalerite changes into the sulphate of zinc, and by other processes into the silicate of zinc, calamine, or the carbonates, smithsonite and hydrozincite.
Sulphides, Tellurides, Etc 89
Syntheses —Sphalerite crystals have been made by the action of upon zinc chloride apor at a high temperature They are also often produced in the flues of furnaces in which ores containing zinc and sul- phur are roasted
Occurrence and Origin — Sphalerite occurs disseminated through lime- stone, in streaks and irregular masses in the same rock, and in veins cut- ting crystalline and sedimentary rocks It is often associated with galena The material in the veins is often crystallized Here it is asso- ciated with chalcopynte (CuFeS2), fluonte (CaF2), bante (BaSCX), sidente (FeCOs), and silver ores When in veins it is in some cases the result of ascending hot waters and in other cases the product of down- ward percolating meteoric water. Much of the disseminated ore is a metamorphic contact deposit.
Localities — Crystallized sphalerite is found abundantly at Alston Moor, Cumberland, England, at vanous places in Saxony, in the Bin- nenthal, Switzerland; at Broken Hill, N S Wales, and in nearly all localities for galena. Handsome, transparent, deavable masses are brought from Pilos de Europa, Santander, Spain. Stalactites are abundant near Galena, 111
The principal deposits of economic importance in America are those in Iowa, Wisconsin, Missouri and Kansas, where the sphalerite is asso- ciated with other zinc compounds and with galena forming lodes in limestone, and at the silver and gold mines of Colorado, Idaho and Mon- tana
Extraction of the Metal — In order to obtain the metal from sphalerite, the ore is usually first concentrated by flotation or other mechanical processes. The concentrates are then converted into the oxide by roast- ing and the impure oxide is mixed with fine coal and placed in clay retorts openmg into a condenser. These are gradually heated The oxide is reduced to the metal, which being volatile distils over into the con- denser, where it is safely caught. Other processes are based on wet chemical methods
Uses of Zinc — Zinc is used extensively in galvanizing iron wire and sheets It is also employed in the manufacture of important alloys such as brass, and in the manufacture of zmc white, which is the oxide (ZnO), and other pigments A solution of the chloride is used for pre- serving timber. Argentiferous zinc is the source of a considerable quan- tity of silver.
Production — The figures showing the quantity of sphalerite pro- duced in the zinc-producing countries are not available The total amount of metallic zmc produced in the year 1912 was 1,070,045 tons,
90 Descriptive Mineralogy
valued at $44,699,166, of which the United States produced from domestic ores 323,907 tons, and in addition used, in the making of zinc compounds, about 55,000 tons Of this aggregate, Missouri produced about 149,560 tons Most of the metal was obtained from sphalerite, but a large part came from other ores The quantity of silver produced in refining zinc ores was 664,421 oz , valued at $408,619
Alabandite (MnS) is isomorphous with sphalerite It usually occurs, however, in dense granular aggregates of an iron-gray color Its streak is dark green It is opaque and brittle Its hardness is 3-4 and density 39 It is not an electrical conductor When heated on charcoal in the reducing flame it changes to the brown oude of man- ganese and finally melts to a brown slag It is soluble ui dilute HC1 with the evolution of EkS Alabandite occurs with other sulphides at Kapnik, Hungary, at Tarma, Peru, at Puebla, Mexico, and m the United States at Tombstone, Arizona, and on Snake River, Summit Co , Colorado
Pentlandite ((Fe Ni)S) may belong to this group Iron is frequently found in crystallized sphalerite Its sulphide, therefore, may be isomor- phous with sphalerite, in \\hich case pentlandite, which is probably an isomorphous mixture of NiS and FeS, would also belong m the sphal- erite group The mineral occurs in light bronzy yellow, granular masses with a distinct octahedral cleavage, a hardness of 3 5-5 and a density of 46 It is a nonconductor of electricity Pentlandite occurs with chalcopynte (CuFeS2) and pyrrhotite (FerSg), at Sudbury, Ontario, where it is probably the constituent that furnishes most of the nickel (seep 92)
It is distinguished from pyrrhotite, which it resembles in appearance, by its cleavage and the fact that it is not magnetic Moreover, it weathers to a brassy yellow color, while pyrrhotite weathers bronze
Wurtzite Division
The wurtzite group comprises only two or three members, wurt.iie (ZnS), greenoMe (CdS), and possibly pyrrhottte (FenSH+1) All crys- tallize m the holohedral division of the hexagonal system and the first two are unquestionably heimmorphic (dihexagonal pyramidal class) Pyrrhotite is the most common.
Wurtzite (ZnS) is one of the dimorphs of ZnS, sphalerite being the other. It occurs in brownish black crystals, m masses and m fibers
Sulphides, Tellurides, Etc 91
Its crystals are combinations of ooP(ioib) with 2(2021) and oP(oooi) at one end, and a series of steeper pyramids at the other Their axial ratio is i : 8175 The a&gk ion Aoili=4o° 9',
2P(022l) A2P(022I) 52° 2Jf
The mineral is brownish black to brownish yellow and its streak is brown Its hardness is between 3 and 4 and its sp gr is about 4 It conducts electricity very poorly In chemical and physical prop- erties it resembles sphalerite Its crystals ha\e been produced by fusing a mixture of ZnSO.4, fluonte and barium sulphide They are frequently observed as furnace products
Wurtzite occurs as crystals at the original Butte Mine, Butte, Montana, and in a mine near Benzberg, Rhenish Prussia, at both places associated sphalerite They also occur \uth silver ores near Oruro and Chocaya, Bolivia, and near Quispisiza, Peru
Greenockite. — Greenockite (CdS) is completely isomorphous with wurtzite Its crystals have an axial ratio i ' 8109 In general habit they are like those of wurtzite but they contain many more planes (Fig 36) The angle ioTiAoiTi 39° 58 Crystals are rare and small The mineral usually occurs as a coating on other minerals, especially sphalerite Its color is honey to orange-yellow, its streak orange- FIG 36 —Greenockite Crys- yellow, and its luster glassy or resinous It tal OOP, ioT<(w), aP,
is transparent or translucent and is brittle 2°?x IOIJLand TII j j A ± °F o001 (c) (The form
Its hardness is 3-3 5 and density about 4 9 ip> Iol2 (l) ls often pres-
Its index of refraction w=2 688 When ent at the upper end of
heated in the closed tube it becomes carmine, the crystals )
but it changes to its original color on cooling.
It yields the usual reactions for sulphur and cadmium, and dissolves
in HC1, yielding H2S
Crystals have been obtained by melting a mixture of CdO, BaS, and CaF2, and by heating cadmium in an atmosphere of EfeS to near fusing point The mineral is a common furnace product Greenockite crystals occur with prenmte at Bishoptown, Scotland, and as coatings on sphalerite in the zinc regions of Missouri and Arkansas, and at Fnedensville, Pennsylvania,
92 Descriptive Mineralogy
Pyrrhotite (FenSn+i)
Pyrrhotite, or magnetic pyrite, occupies the anomalous position of being one of the most important ores of nickel, whereas it is essen- tially a sulphide of iron The name is really applied to a series of compounds whose composition ranges between FesSo and Feu>Si7 The crystallized material is in some cases FerSs, and in others, FenSi2 It is probably a solid solution of FeS2 or S in the sulphide of iron (FeS) As usually found, pyrrhotite is in bronze-gray granular masses, that tarnish rapidly to bronze on exposure to the air Good crystals of the mineral are rare.
Analyses of pyrrhotite vary widely The percentages of Fe and S corresponding to FeySs are Fe, 60 4, S, 39 6, and those corresponding to FenSi2 are Fe, 61 6, S, 38 4 Much of the mineral contains in addi- tion to the iron and sulphur sufficient nickel to render it an ore of this metal, but it is probable that the nickel is present in pentlandite (see p 90) or some other nickel compound embedded in the pyrrhotite
Analyses of pyrrhotite from various localities are
S Fe Co Ni Total
Schneeberg, Saxony 39 10 6r 77 tr 100 87
Brewster, NY 37 98 61 84 25 100 07
Sudbury, Ontario 38 91 56 39 4 66 99 96
Gap Mine, Penn. 38 59 55 82 5 59 100 oo
The few crystals of pyrrhotite known are distinctly hexagonal in habit with a c=i i 7402 They are com- monly tabular or acutely pyramidal, but it has not been established that they are hemi- morphic, although the almost universal pres- ence of FeS in crystals of wurtzite would FIG 37 -Pyrrhotite Crystal mdlcate that the two substances are isomor- oP, oooi (c), P, ion (s); , , , . f
4P, 4041 and COP, Phous The tabular crystals possess a broad I0lo (m) basal plane, which surmounts hexagonal prisms
ooP(ioTo) and oop2(ii2o); and a series of
pyramids, of which 2P(2O2i), JP(ioT2), P(ioli) and P2(ri22) are the most frequent (Fig 37 ) The angle loli AoiTi S3°
The cleavage of pyrrhotite is not always equally distinct When marked it is parallel to ooP2(ii2o) There is also often a parting parallel to the base Its fracture is uneven The mineral is brittle. It is opaque, and has a metallic luster Its color varies between bronze-
Sulphides, Tellurides, Etc 93
yellow and copper-red, and its streak is grayish black Its hardness is a little less than 4 and its density about 4 5 All specimens are magnetic but the magnetism varies greatly in intensity, being at a maximum in the direction of the vertical axis The mineral is a good conductor of electricity.
Pyrrhotite gives the usual reactions for iron and sulphur, and some- times, in addition, the reactions for cobalt and nickel It is decom- posed by hydrochloric acid with the evolution of EbS, which may easily be detected by its odor.
From the many sulphides more or less closely resembling pyrrhotite in appearance, this mineral may easily be distinguished by its color and density and by its magnetism
Syntheses — Crystals may be obtained by heating iron wire or Fes04, or dry FeCk to redness in an atmosphere of dry HoS and by heating Fe in a closed tube with a solution cf FcCls saturated with H2S
Occurrence, Locdtes and Origin — Pyrrhotite occurs completely filling vein fissures, and also as crystals embedded in other minerals constituting veins It occurs also as impregnations in various rocks and as a segregation in the coarse-grained basic rock known as nonte, where it is believed to have separated from the magma producing the rock It may also in some cases be a product of metamorphism on the borders of igneous intrusions
It is found at Andreasberg, Harz, Bodenmais, Bavaria, Minas Geraes, Brazil, various points in Norway and Sweden, and on the lavas of Vesuvius In North America crystals occur at Standish, Maine, at Trumbull, Monroe Co , N Y , and at Elizabethtown, Ontario The mineral has been mined at Ducktown, Tenn , at Ely, Vermont, and at Gap Mine, Lancaster Co , Penn
Its mines at present, however, are at Sudbury, in Ontario, where the mineral is associated with magnetite, chalcopynte and pentlandite ((Fe Ni)S) on the lower border of a great mass of igneous rock (norite). Besides these there are present also embedded in the pyrrhotite small quantities of other minerals, so that the ore as mined is very complex.
Pyrrhotite is sometimes found altered to pyrite, to limomte and to siderite (FeC03)
Extraction — Pyrrhotite is crushed and roasted to drive off the greater portion of the sulphur It is then placed in a furnace and smelted with coke and quartz The nickel, copper and some of the iron, together with some of the fused sulphides, collect as a matte in the
94 Descriptive Mineralogy
bottom of the furnace from which it is withdrawn from time to time The matte is next roasted to transform the iron it contains into oxides and the remaining nickel and copper are separated by patented or secret methods
Uses —The mineral is sometimes worked for the sulphur it con- tains Its principal use, however, is as a source for nickel, nearly all of this metal used in America coming from the nickehferous variety found at Sudbury, Ontario
The metal nickel has come into extensive use in the past few years in connection with the manufacture of armor plate for warships The addition of a few per cent of nickel to steel hardens it and increases its strength and elasticity
Nickel is also extensively used in mckel-platmg and in the manufac- ture of alloys German silver is an alloy of nickel, copper and zinc The nickel currency of the United States contains about 25 per cent Ni and 75 per cent Cu Monel metal is a silver-white alloy containing about 75 per cent Ni, i per cent Fe and 29 per cent Cu It is stronger than ordinary steel, takes a brilliant finish and is impervious to acids It is made directly at Sudbury, Ont , by smelting
Production —The production of pyrrhotite and chalcopyrite (CuFeS) at the Sudbury mines in 1912 amounted to 737,584 short tons The value of the matte produced was $6,303,102, and the value of nickel con- tained in it was about $16,000,000 About half of the nickel was used in America, the remainder, amounting to $8,515,000, was exported, after being refined in the United States Formerly the United States pro- duced a considerable quantity of nickel from domestic ores, most of it from pyrrhotite, but the mines have been closed down within the past few years. It is, however, produced as a by-product in the refining of copper ores to the amount of about 325 tons annually, This is worth about $260,000 (see also p, 400).
Millerite Group
This group comprises sulphides, arsenides and antimonides of nickel. It includes the minerals millmte (NiS),mccohte (NiAs), ante (Ni(Sb As)) bwthauptite (NiSb) and a few others Of these only millente and nic- colite are at all common The minerals all crystallize m the hexagonal system, possibly in the rhombohedral division (ditrigonal scalenohedral class). Well defined crystals are, however, rare and often capillary so that their symmetry has not been determined with certainty.
Sulphides, Tellurides, Etc 95
Mfflerite (NiS)
Millerite is easily recognized by its brass-yellow color It occurs most frequently in slender hair-like needles, often aggregated into tufts or radial groups, or, woven together like wads of hair, forming coatings on other minerals
Pure millente contains 35 3 per cent sulphur and 64.6 per cent nickel It frequently contains also a little Co and Fe.
Crystals are thin, acicular or columnar with prismatic and rhom- bohedral faces predominating, and an axial ratio of i 330, or of i : 9886 if the rhombohedron 311(0331) is taken as the ground form
The mineral is elastic Its hardness is 3-3 5 and density about 5 5. It is opaque and brassy yellow Its streak is greenish black. It is an excellent conductor of electricity
The mineral yields sulphurous fumes in the open tube. After roast- ing it gives, with borax and microcosmic salt, a violet bead when heated in the oxidizing flame of the blowpipe On charcoal with NaaCOs it yields a magnetic globule
Synthesis — Bunches of yellow acicular crystals of N1S have been formed by treatment of a solution of NiSO with HS, under pressure.
Localities — Millerite occurs as long acicular crystals in cavities in other minerals at Joachimthal, in Bohemia, and at many places in Saxony In the United States it forms radiating groups in cavities in hematite (F&Os) at Antwerp, NY At the Gap Mine, Lancaster Co , Penn , it forms coatings on other minerals and at St Louis, Mo and at Milwaukee, Wis , it occurs in delicate tangled tufts in geodes in lime- stone, Nowhere does it occur in sufficient quantity to constitute an ore.
Niccolite (NiAs)
Niccolite usually occurs massive, though crystals are known It is of economic importance only in a few localities
Theoretically, the mineral contains 56 10 per cent As and 43 90 per cent Ni, but as usually found it contains also Sb, S, Fe and often small quantities of Co, Cu, Pb and Bi
Its crystals, which are rare, are hexagonal and hemimorphic (prob- ably dihexagonal pyramidal class), with a : c=i : 8194 The prism ooP(ioTo), and oP(oooi) are the predominant forms, with the pyramids P(ioTi) and (5057) less well developed The angle
The mineral is pale copper-red and opaque It has a brownish
96 Descriptive Mineralogy
black streak. Its hardness is about 5 and its density 7 6 The surfaces of nearly all specimens are tarnished with a grayish coating The min- eral is a good conductor of electricity
In the open tube mccohte yields arsenic fumes and often traces of 862 On charcoal with Na2COs it yields a metallic globule of nickel It dissolves in HNOs with the precipitation of AsgOa The apple-green solution, thus produced, becomes sapphire-blue on addition of ammonia
Its peculiar light pink color and its reactions for arsenic and nickel distinguish mccohte from all other minerals, except, perhaps, breit- kaupttte, which, however, contains antimony
Occurrence — Niccohte occurs principally in veins in crystalline schists and in metamorphosed sedimentary rocks, associated with silver and cobalt sulphides and arsenides
Localfoes — The principal locality for mccohte in North America is Cobalt, Ontario, where it is found with native silver and silver, cobalt, and other nickel compounds, all of which are thought to have been de- posited by hot waters emanating from a mass of diabase In Europe it is abundant at Joachimsthal in Bohemia, and at a number of other places in small quantity
Although rich in nickel, the mineral is not used as an ore at present, except to a very minor extent, most of the nickel of commerce being obtained from other compounds (see p 94)
Breithauptite (NiSb) is rare It is of a light copper-red color, much brighter than that of mccohte, and its streak is reddish brown Its hard- ness is 5 5 and density about 7 9 Its crystals are hexagonal tables with an axial ratio i i 294, and a distinct cleavage parallel to oP(ooi) It usually occurs m dendritic groups, m foliated and finely granular aggregates and in dense masses It is a frequent furnace product, when ores containing Ni and Sb are smelted It is found at Andreasberg, Harz , at Sarrabus, m Sardinia, at Cobalt, Ont , and at a few other places It is distinguished from mccohte by its deeper color and its content of Sb.
Covelhte (CuS)
Covellite, or indigo copper, is the cupric sulphide, chalcocite being the corresponding cuprous salt It is called indigo copper because of the deep blue color of its fresh fracture. It is often mixed with other copper compounds from which it has been derived by alteration It usually occurs massive, but crystals are known It is an unimportant ore of copper.
Sulphides, Tellurides, Etc 97
The theoretical composition of the mineral is 33 56 per cent S, 66 44 per cent Cu It usually, however, contains also a little iron and often traces of lead and silver
Crystals of covellite are not common. They are hexagonal a c-i 3 972 and their habit is usually tabular The forms observed are oP(oooi), oo P(iolo), P(ioTi) and JP(ioT4) icTi /\oi Ti 77° 42'.
The mineral has one perfect cleavage parallel to oP(oooi) In thin splinters it is flexible Its hardness is i 5-2 and density about 4 6 Its color is dark blue and its streak lead-gray to black It is opaque, with a luster that is sometimes nearly metallic, but more frequently dull It is a good electrical conductor
The blowpipe reactions of covellite are like those of chalcocite, with these exceptions Covellite burns ith a blue flame when heated on charcoal, and yields a sublimate of sulphur in the closed tube
Covellite is distinguished from other minerals than chalcocite by its reactions for Cu and S and the absence of reactions for Fe. It is distinguished from chalcocite by its color and density and by the fact that it ignites on charcoal
Syntheses — The treatment of green copper carbonate with water and EkS in a closed tube at 8o°-9o° yields small grains of covellite The mineral has also been produced by the action of HsS upon vapor of CuCl2, and by treating sphalerite with a solution of copper sulphate in a sealed glass tube containing C02 at a temperature of iso°-i6o° for two days
Localities and Origin— The mineral is comparatively rare It is abundant in Chile and Bolivia and at Butte, Mont , and is found in crystals on the lava of Vesuvius and elsewhere It usually occurs as an alteration product of other copper-sulphur compounds, especially in the zone of secondary enrichment of copper veins
Uses — It is mined with other compounds and used as a source of copper,
Cinnabar Group
This group comprises sulphides, selenides and tellundes of mercury The group is dimorphous, with its members crystallizing in henuhedrons of the isometric system (hextetrahedral class) and in tetartohedrons of the hexagonal system (trigonal trapezohedral class) The isometric HgS is known as metacmnabante and the hexagonal form as cinnabar Only the latter is important In addition to these are known the rare compounds onofnte (Hg(S Se)), tiemanmte (HgSe) and coloradcnte (HgTe), all of which are isometric
Descriptive Mineralogy
Cinnabar (HgS)
Cinnabar is the only compound of mercury that occurs in sufficient quantity to constitute an important ore Nearly all of the mercury, or quicksilver, in the world is obtained from it The mineral occurs both crystallized and massive The ore is a red crystalline mass that is easily distinguished from all other red minerals by its peculiar shade of color and its great weight.
Theoretically, it contains 13 8 per cent S and 86 2 per cent Hg Massive cinnabar is, however, usually impure through the admixture of clay, iron oxides or bituminous substances Occasionally the quan- tity of organic material present is so large that the mixture is inflam- mable.
Though cinnabar is usually granular, massive or earthy, it some- times occurs beautifully crystallized in small complex and highly modi- fied hexagonal crystals that exhibit tetartohedral forms (trigonal trape- zohedral class) Usually the crys- tals are rhombohedral or prismatic m habit Their axial ratio is i . i 1453 Planes belonging to more than 100 distinct forms have been observed, but the crystals on which they occur aie usually so small that few of them are of im- portance as distinguishing charac- teristics. The prismatic crystals, which are the most common in this country, are often bounded by ooR, (rolo) and £R, (4045) (Fig 38) Others, however, are very complicated Their cleavage is perfect parallel to oo R(ioTo).
The mineral is slightly sectile It is transparent, translucent or opaque, is of a cochineal-red color, often inclining to brown, and its streak is scarlet Its hardness is only 2-2 5 and its density about 8 i It is circularly polarizing and is a nonconductor of electricity Its dimorph, metacinnabante, on the other hand, is a good conductor The indices of refraction of cinnabar are co= 2 854, 201
When heated gently in the open tube cinnabar yields sulphurous fumes and globules of mercury. On charcoal before the blowpipe it volatilizes completely.
There are only a few minerals with which cinnabar is likely to be
FIG 38 -Cinnabar Crystals with R, iolo (m), fR, 4045 (0, £R, 2025 (/), R, loTi (0 and o&, oooi (c)
Sulphides, Tellurides Etc 99
confused, since its color and streak are so characteristic From all red minerals but realgar it may easily be distinguished by its sulphur reaction From realgar it is distinguished by its great density and its greater hardness
Pseudomorphs of cinnabar after stibnite, dolomite ((Ca Mg)COsJ, pynte and tetrahednte (a complicated sulpho-salt) have been described
Synthesis — Crystals ha\ e been made heating mercury in an aque- ous solution of HbS
Occurrence Localities and On gin — Cinnabar is usually found in veins cutting serpentine, limestones, slates, shales and \anous schists It is associated \Mth gold, various sulphides, especially pynte and mar- casite (FeS2) calcite (CaCOs), barite (BaSO-i), fluonte (CaF2) and quartz It is also found impregnating sandstones and other sedimen- tary rocks, and sometimes as a deposit from hot springs Its deposi- tion is thought to be the result of precipitation from ascending hot
Crystallized cinnabar occurs at a number of places in Bohemia, Hungary, Serbia, Austria, Spam, California, Texas, Nevada, and at ether localities m Europe Asia and South America
The principal deposits of economic importance are at Almaden in Spain, at Idria in the Province of Carmola, Austria, at Bakhmut in southern Russia, at various points along the Coast Ranges in Cal- ifornia, in Esmeralda, Humboldt, Nye and Washoe Counties in Nevada, at many points in Oregon and Utah, and at Terhngua in Texas The mineral is also abundant in Peru and in China but in these countries it has not yet been mined profitably The California cinnabar district extends for many miles along the Coast Ranges, but at only about a dozen places is the mineral mined
The Spanish mines, near the city of Cordova, have been worked for many hundreds of years Much of the ore is an impregnation of sandstone and quartzite — the mineral sometimes comprising as much as 20 per cent of the rock mined
Extraction — The metallurgy of cinnabar is exceedingly simple It consists simply in roasting the ore alone, or mixed with limestone, and conducting the fumes into a condensing chamber that is kept cool. The sulphur gases are allowed to escape through the chamber in which the mercury is collected
Uses of Metal — Mercury finds many uses in the arts Its most im- portant one is in the extraction of gold and silver by the amalgamation process It is the essential constituent of the pigment vermilion, which is a manufactured HgS. In its metallic state it is largely employed in
100 Descriptive Mineralogy
the making of mirrors, of barometers, thermometers and other physical instruments Some of the salts are important medicinal preparations while others are used in the manufacture of percussion caps
Production —The world's annual production of quicksilver, all of which is obtained from cinnabar, is not far from 4,000 metric tons The United States produced 940 tons in 1912, valued at $1,053,941 Of this total California yielded 20,524 flasks of 75 Ibs each, valued at about $863,034, and Texas and Nevada 4,540 flasks valued at $190,907 To produce these quantities of metal California mined I39>347 tons of ore and Texas and Nevada 16,346 tons The California ore yielded n Ibs of metal per ton and the Nevada and Texas ore 20,8 Ibs,
Metacmnabarite (HgS) is generally found as a gray-black massive mineral with a black streak It is brittle, has a hardness of 3 and a density of 7 8 It is associated with cinnabar at some of the mines in California and Mexico, and at a few places in other countries It is exceedingly rare.
The Metallic Disulphides, Diselenides And Diarsenides
The disulphides, diselemdes, ditellundes, diarsemdes and dianti- monides differ from the corresponding monocompounds m that they contain double the quantity of S, Se, Te and Sb They are divisible into two groups, one of which comprises sulphides, arsenides and anti- monides of iron, manganese, cobalt, nickel and platinum, and the other the tellundes and selemdes of gold and silver,
Glanz Group
The glanz group is an excellent illustration of an isodimorphous group. Its members are characterized by their hardness, opaqueness, light color and brilliant luster. Hence the name of the group In composition the minerals belonging to the group are sulphides, arsenides or anti- momdes of the iron-platinum group of metals, with the general formula RQ2 in which R is Mn, Fe, Ni, Co, Pt, and Q=S, As and Sb The com- position of the more simple members may be represented by the formula
/S Fe/ , and of those in which arsenic or antimony replaces a part of the
S y
It is probable, however, that some of the cobalt and nickel arsenides
Sulphides, Tellurides, Etc 101
are mixtures and that their indicated compositions are only approximate All members of the group are believed to be dimorphous, crystallizing in the isometric (dyakisdodecahedral class), and in the orthorhombic systems (orthorhombic bipyramidal class), though not all have as yet been found in both forms The most important members of the group, as at present constituted, are as follows
Isometric Orthorhombic
Pynte FeSg Marcasite
Hauente MnS2
FeAsS Arsenopyrite
FeAs2 Lolhngite
CobalMe CoAsS Glaucodot
Gersdor/tte (Ni Fe)AsS
Korymte (Ni Fe)(As Sb S)2 Wolfachite
Ullmamte NiSbS
Smdtite CoAs2 Safflonte
Ckloanthite NiAs2 Rammdsbergite
Sperryhte PtAs2
The group is divided into two subgroups, the regularly crystallizing minerals forming the pynte group and the orthorhombic ones the mar- casite group The most important members of the former group are pynte, cobaltite, smaltite and chloanthite The most important members of the marcasite group are marcastte, arsenopynte and lolhngite.
Pyrite
The crystallization of the pyrite group is in the parallel heimhedral division (dyakisdodecahedral class) of the isometric system. The
occurrence of the form - , 210, is so frequently seen on the mineral
pyrite that it has received the name pyritoid
The group is so perfectly isomorphous that a description of the forms on one member is practically a description of the forms on all.
Pynte (FcS2)
Pyrite, one of the most common of all minerals, is found under a great variety of conditions as crystals, as crystalline aggregates and as crystalline masses It occurs under practically all conditions and in all situations It is easily recognized by its bright yellow color, its brilliant luster and its hardness,
Descriptive Mineralogy
Pyrite containing, theoretically, 46 6 per cent of iron and 53 4 per cent of sulphur is usually contaminated with small quantities of nickel,
FTC 39 — Group of Pyrite Crystals in which the Cube Predominate The c
are striated parallel to the edge between oo 0 oo (100) and I — — ) , (210)
cobalt, thallium and other elements An auriferous variety is worked for gold, yielding in the aggregate a large quantity of the precious
FIG 40 IK, 4i
FIG 40 — Pynte Crystals on which 0 (in) Predon mates o=0, n i and c
FIG 41 — Pynte Crystal with oo 02, 210 (e) and 0, in (a)
metal Sometimes arsenic is present in small quantity Analysis of the crystals from French Creek, Penn , gave
8=5408, As=o 20, Fe=44 24, Co=i 75, Ni=o 18, Cu=oos, =100 50.
Sulphides, Telluride3, Etc
The number of forms that have been observed on pynte crystals is
very large Hintze records 86 The cube and the pyntoid I
L 2 J
FIG 42 — Group of Pynte Crystals in \\hich ooQ2 (210) Predominates Daly- Judge Mine, near Park City, Utah (After J W Bmtfaett )
From
(210) are the most common of these, though the octahedron and the
dodecahedron are not rare Four distinct types of crystals may be
recognized, viz those with the cubic (Fig 39),
the octahedral (Fig. 40), and the pyntoid
habits (Figs 41 and 42), and those that are
interpenetrating twins (Fig 43) The cubic
and the pyritoid planes are often striated
parallel to the edges between these faces The
interpenetrating twins are twinned about the
plane 0(ni)
The cleavage of pynte is imperfect and its fracture conchoidal. The mineral is brittle Its hardness is 6-6 5 and density about 5. Its luster is very brilliant and metallic Its color is brassy yellow and its
streak greenish or brownish black With steel it strikes fire, hence its name from the Greek word meaning fire. It is a good conductor of electricity and is strongly thermo-electric.
FIG 43 — Pynte Interpene- trationTwin Two Pyn- toids ( Os, 210) Twinned about O in
In the closed tube pynte yields a sublimate of sulphur and a residue that is magnetic On charcoal sulphur is freed This burns with the blue flame characteristic of the substance The globule remaining after heating for some time is magnetic Treated with nitric acid the mineral dissolves leaving a flocculent residue of sulphur, which when dried and heated may readily be ignited
Pynte in some of its forms so closely resembles gold that it is often known as fool's gold There is, of course, no difficulty in distinguishing between the two metals, since pyrite contains sulphur and is soluble in nitric acid, while gold contains no sulphur and is insoluble in all simple acids.
The mineral is most easily confounded with chako pynte (CuFeS>), though the difference in hardness of the two easily serves to distinguish them Chalcopynte may be readily scratched with a knife blade or a file, while pyrite resists both The latter mineral, moreover, contains no copper
Syntheses — Small crystals of pyrite are produced by the action of HaS on the oxides or the carbonate of iron enclosed in a sealed tube heated to 8o°-9o°, also by the passage of EbS and FeCla vapors through a red-hot porcelain tube.
Occurrence and Origin— Pynte occurs in veins and as grains or crystals embedded in all kinds of rocks. In rocks it usually appears as crystals, but in vein-masses it may appear either as crystals, with other minerals, or as radiating or structureless masses occupying entirely the vein fissures In slates it often occurs in spheroidal nodules and concretions of various forms, and also as embedded crystals. The mineral is the product of igneous, metamorphic and aqueous agencies
Pyrite weathers readily to hmonite. In ore bodies near the surface it is oxidized. A portion of the mineral changes to FeSQt which percolates downward and aids in the concentration of any valuable metals that may be present m small quantity in the ore. Another portion of the iron remains near the surface in the form of lunonite This covering of oxidized material is known as the " gossan " and it is characteristic of all pyrite deposits
Localities — Pynte crystals are so widely distributed that but very few of its most important occurrences may be mentioned here In the mines of Cornwall, Eng , and in those on the Island of Elba very large crystals are found Fine crystals also come from many different places in Bohemia, Hungary, Saxony, Peru, Norway, and Sweden
In the United States the finest crystals are at Schoharie and Rossie, N Y ; at the French Creek mines in Chester Co , and at Cornwall,
Sulphides, Telluride3, Etc 105
Lebanon Co , Penn , and near Greensboro and Guilford Co , X Carolina Massive pyrite occurs in great deposits at the Rio Tmto mines in Spain, at Rowe, Mass , in St Lawrence and Ulster counties, X Y , in Louise Co , Va , and in Pauldmg Co , Ga Much of the massive pynte in the veins of Colorado, California and of the southern states, from Virginia to Alabama, is auriferous and much of it is mined for the gold it contains
Uses — Pynte is used principally in the manufacture of sulphuric acid The mineral is burned in furnaces and the 862 gases thus result- ing are carried to condensers \\here they are oxidized by fineh divided platinum or by the oxides of nitrogen The residue, which consists largely of Fe20s, is sometimes smelted for iron or made into paint This residue also contains the gold and other \aluable metals that may have been in the original pyrite.
The sulphuric acid obtained from pyrite enters into many manu- facturing processes The greater portion of it is consumed in the artificial fertilizer industry
Production — Pyrite is mined in the United States in Franklin Co , Mass , in Alameda and Shasta Counties, California, in Louisa, Pulaski and Prince William Counties, Va , in Carroll Co , Ga 3 in St Lawrence Co , N Y , m Clay Co , Alabama, and at the coal mines in Ohio. Illinois and Indiana where it is a by-product The total production of the United States in 1912, amounting to 330,928 long tons, was \alued at $1,334,259 Virginia is by far the largest producer In addition to this quantity the trade consumed 970,785 tons of imported ore, most of which came from Spain, and utilized the equivalent of 260,000 tons of pynte m the shape of low grade sulphide copper ores from Ducktown, Tenn , and zinc sulphide concentrates from the Mis- sissippi Valley and elsewhere for the manufacture of sulphuric acid. The total amount of sulphuric acid manufactured in the United States during 1912 was 2,340,000 short tons, valued at $18,338,019 The total world production of pyrite is about 2,000,000 tons annually
Small quantities of the mineral are also mined for local consumption in Lumpkin Co , Georgia, and near Hot Springs, Arkansas Much aunferous pynte has also been mined in the southern states and the Rocky Mountain region for the gold it contains This metal is sepa- rated from the pyrite partly by crushing and amalgamation and partly by smelting or by leaching processes. In the former case the gold occurs as inclusions of the metal in the pynte.
106 Descriptive Mineralogy
Cobaltite (CoAsS)
Cobaltite is a alver-nvhite or steel-gray mineral occurring in massive forms or in distinct crystals exhibiting beautifully their hemihedral character It is completely isomorphous with the corresponding nickel compound, gersdorffite (NiAsS), and consequently mixtures of the two are common
Cobaltite usually contains some iron and often a little nickel Theoretically, it consists of 19 3 per cent S, 45 2 per cent As and 35 5 Co The compositions of a massive variety from Siegen, Westphalia, and that of crystals from Nordmark, Norway, are as follows
As S Co Fe Ni Total
Siegen 45 31 19 35 33 71 i 63 100 oo
Nordmark 44 77 20 23 29 17 4 72 i 68 100 57
The crystallization of cobaltite is perfectly isomorphous with that of pyrite, though the number of its forms observed is far smaller The
most common planes are those of oo 0 oo (100) , 0(i 1 1 ) and (210)
The cleavage of cobalt is fairly good parallel to oo 0 oo (100) Its fracture is uneven, its hardness is 5 5 and its density about 6 2 The color of the mineral, as stated above, varies between silver-white and steel- gray Its streak is grayish black It is a good conductor of electricity
In the open tube cobaltite reacts for S and As On charcoal it yields a magnetic globule which when fused with borax on platinum wire yields a deep blue bead It weathers fairly readily to the rose- colored cobalt arsenate known as erythnte (Coa(As04)2 SEfeO)
By its crystallization and color cobaltite is distinguished from nearly all other minerals but those of the same group From most of these it is easily distinguished by its blowpipe reactions foi sulphur, arsenic and cobalt
Occurrence and Origin — Cobaltite occurs mainly m veins that are believed to have been filled by upward moving solutions emanating from igneous rocks It is associated with compounds of nickel and other cobalt compounds and with silver and copper ores
Localities — Cobaltite is not very widely distributed Large, hand- some crystals occur at Tunaberg in Sweden, at Nordmark, Norway, at Siegen, Westphalia, and near St Just in Cornwall, England It is found also in large quantity at Cobalt, Ontario, associated with silver ores and nickel compounds
Sulphides, Tellurides Etc 107
Uses — Cobaltite is said to be used jewelers in India in the pro- duction of a blue enamel on gold ornaments It is employed also in the manufacture of blue and green pigments and in the manufacture of com- pounds used in small quantity in the various arts Smalt is the most valuable of the cobalt pigments and is at present the chief commercial compound of this metal It is a deep blue glass that cheers from ordinary glass in containing cobalt in place of calcium Smalt is made from cobaltite and from other cobalt ores fusion a mixture of quartz and potassium carbonate Certain cobalt compounds are sug- gested as excellent driers for oils and varnishes The mineral is also utilized as an ore of cobalt, \\hich in the form of stelhte, an alloy com- posed of 70 per cent cobalt, 15 per cent chromium and 15 per cent molybdenum or tungsten, bids fair to acquire a large use as a material for the manufacture of table cutlery and edged tools The use of the metal has also been suggested as a material for coinage in place of nickel.
Production — Most of the cobalt of commerce is handled by the trade in the form of the oxide It is produced from the anous cobalt minerals, mainly as a by-product in the extraction of nickel, and hence ver> little is obtained from cobaltite The mines at Cobalt, however, have furnished a large quantity of cobaltite and smaltite \uthin the past few years and these have gone into the manufacture of the oxide, of which about 515 tons -\\ere produced in 1912, ha\mg a \alue of $317,165
Smaltite (CoAs>)
Smaltite is another important ore of cobalt It is found in crystals and masses
Its theoretical composition is 71 88 per cent As and 28 12 per cent Co, though it usually contains also S, Ni, Fe and frequently traces of Bi, Cu and Pb Since it is isomorphous \uth the arsenide of nickel chloanthite (NiAs2), mixed crystals of the are common Moreover, sharply defined crystals have been found to consist of mechanical mix- tures of several compounds
Smaltite occurs in small crystals of cubical habit with ooOoo (100), 0(in) and various pyritoids predominating
The mineral is tin-white to steel-gray, and opaque, and has a grayish black streak It is often covered ith an iridescent or a gray tarnish. Its cleavage is indistinct, its fracture uneven, its hardness 5-6 and density 6 3-7 It is a good electrical conductor
Before tie blowpipe on charcoal smaltite yields arsenic fumes and a
108 Descriptive Mineralogy
magnetic globule of metallic cobalt It is soluble in HNOs, yielding a rose-colored solution and a precipitate of As2Os
The mineral is fairly easily distinguished from most other minerals by its color and blowpipe reactions From cobaltite it is distinguished by the lack of S From a few others that are not described in this volume it can be distinguished by its crystallization or by quantitatn e analysis
Synthesis — Smaltite crystals are produced when hydrogen acts at a high temperature upon a mature of the chlorides of cobalt and arsenic
Occurrence and Ongm —Smaltite is found associated with cobaltite in nearly all of its occurrences It is especially abundant at Cobalt, Out As in the case of most other cobalt minerals, its presence is indicated by deposits of rose-colored erythnte which coat its surfaces wherever these are exposed to moist air Its methods of occurrence, origin and uses are the same as for cobaltite (p 107).
Chloantfaite (NiAso) resembles smaltite in most of its characteris- tics The two minerals grade into each other through isomorphous mixtures Those mixtures in which the cobalt arsenide is in excess are known as smaltite, while those in which NiAs predominates arc called chloanthite The pure chloanthite molecule is Ni= 28 i per cent, As 1 9 per cent
The two minerals can be distinguished when unmixed with one another by the blowpipe reactions for Co and Ni In mixed ciysUis the predominance of one or the other arsenides can be determined only by quantitative analysis
Chloanthite containing much iron is distinguished as thathamite, from Chatham, Conn , where it occurs with arsenopynte and niccohte in a mica-slate
The mode of occurrence of chloanthite and the localities at which it is found are the same as in the case of smaltite.
Spenyhte (PtAs2)
Sperryhte is extremely rare It is referred to here because it is the only platinum compound occurring as a mineral Chemically, it is 43 S3 Per cent As and 56 47 per cent Pt, but it contains also small quan- tities of Sb, Pd and Fe
Its crystals are simple They contain only 0(iu), ooOoo(ioo), oo 0(no) and several pyntoids Their habit is usually octahedral or cubical
The mineral is opaque and tin-white, and its streak black Its hard- ness is 6-7 and density 10 6
Sulphides, Telluride3, Etc 109
In the closed glass tube it remains unchanged, but in the open tube it gives a sublimate of AsOs When dropped upon red-hot platinum foil it immediately melts, giving rise to fumes of As20s, and forming blisters on the foil that are not distinguishable from the original platinum in color or general character It is soluble in concentrated HC1 and aqua regia
Synthesis — The mineral has been produced by leading arsenic fumes over red-hot platinum in an atmosphere of h\drogen
Occurrence and Localities — Sperrylite occurs as little crystals com- pletely embedded in the chalcopynte (CuFeSo) and the gossan of a nickel mine, and in the chalcop\nte of a gold-quartz vein near Sudbury, Ontario, in covelhte at the Rambler Mine, Encampment, \V\ormng, and as flakes in the sands of streams in the Co\\ee Valle\ , Macon Co , Ga The flakes resemble very close,!} native platinum, from which they are of course, easily distinguished by the test for arsenic
Uses — The sperryhte from Sudbury and ommg furnish much of the platinum produced in the United States (see p 64)
MARCASITE Dl\ ISIOX
Three members of the marcasite group are important, all are inter- esting from the fact that they are so alike in their cr\stalhzation that a description of the forms belonging to any one of them might serve as a description of those belonging to all others The crystallization of the group is orthorhombic (rhombic bipyramidal class), with an axial ratio approximately a b ' 7 1:12
Marcasite (FeS2)
Marcasite, the dimorph of pynte, resembles this mineral so closely that in massive specimens it is difficult to distinguish between the two They are nearly alike in hardness, in color and in chemical properties Marcasite is a little lighter m color than pynte Its density is less (about 4 9), and it possesses a greater tendency to tarnish on exposed surfaces
This tarnish indicates that the mineral is more susceptible to altera- tion than is pynte One of the products of this alteration is ferrous sul- phate, which may often be detected by its taste upon touching the tongue to specimens of the mineral In crystallized specimens there is not the least difficulty in distinguishing between them, suice their crystallization is very different
Marcasite is orthorhombic (rhombic bipyramidal class), with the
Descriptive Mineralogy
axial ratio 7662 i i 2342 Its simple crystals often possess a tabular or a pyramidal habit (Figs 44 and 45) In the former case oP(ooi) is the predominant face, and m the latter case the two domes P 60 (101)
Fig 44 Fig 45
FIG 44— Marcasite Crystal with °oP,no(w), oP,ooi(c), Po , on (/) and JPS5 ,
013 (T)
FIG 45 — Marcasite Crystal with Forms as Indicated in Fig 44, and P M , 101 (e)
and P, in (s)
andP <56 (on) The other forms observed on most crystals are oo P(iio), P(III), and often oo (013)
Twins are very common, with oo P(no) the twinning plane (Fig 46) Sometimes these are aggregated by repeated twinning into serrated groups known as cockscomb twins or spearhead twins (Fig 47), because
Fig 46 Fig 47
FIG 46 —Twin of Marcasite about oo P(iio)
FIG 47 — Spearhead Group of Marcasite Fourling Twinned about no and then
about i To
of the outlines of their edges. In many instances the crystals aie acic- ular or columnar in habit, forming radiating groups with globular, rem- form and stalactitic shapes Concretions are also common The basal plane is usually striated parallel to the edge between it and P oo (on) The cleavage is distinct parallel to oo P(iio) The fracture is uneven
SULPHIDES, TELLURIDES, ETC. Ill
When powdered marcasite is treated cold nitric acid and allowed to stand, it decomposes \uth the separation of sulphur
Marcasite readih alters to limonite The fact that pyrite, sphaler- ite, chalcopyrite, and other minerals form pseudomorphs after it indicates that, under suitable conditions, it alters also to these com- pounds The mineral is in most cases a direct result of precipitation from hot solutions
Synthesis — Marcasite crystals ha\e been prepared by the reduction of FeSQi by charcoal in an atmosphere of EfeS
Occurrence ani Uses — The mineral, like pyrite, is found embedded in rocks in the form of crystals and concretions, and also as the gangue masses of veins It constitutes nearly the entire filling of some veins, and forms druses on the walls of cavities in both rocks and miner- als It also replaces the organic matter of fossils preserving their shapes — thus producing true pseudomorphs
When associated pyrite it is mined together this mineral as a source of sulphur
Localities — Crystalline marcasite occurs m such great quantity near Carlsbad m Bohemia that it is mined The cockscomb variety is found in Derbyshire, England, and crystals at Schemmtz in Hungary and at Andreasberg and other places in the Harz In the United States the mineral occurs as crystals at a great number of places, being par- ticularly abundant m the lead and zinc localities of the Mississippi Valley, where it sometimes forms stalactites The stalactites from Galena, 111 , often consist of concentric layers of sphalerite, galena and crystallized marcasite
Arsenopyrite (FeAsS)
Arsenopyrite, or mispickel, is the most important ore of arsenic It is found in crystals and in compact and granular masses. It is a silver-white metallic mineral resembling very closely cobaltite in its general appearance
The formula FeAsS for arsenopynte is based on analyses like the following.
As S Fe Total
Specimen from Hohenstein, Saxony 45 62 19 76 34 64 100 02 Specimen from Mte Chalanches, France 45 78 ig 56 34 64 99 98
Theoretically, the mineral consists of its components m the following proportions, As 46 per cent, S 19 7 per cent, Fe 34 3 per cent In many specimens the iron is replaced in part by cobalt, nickel or manganese.
Descriptive Mineralogy
Sometimes the cobalt is present in such large quantity that the mineral is smelted as an ore of this metal
The axial ratio of arsenopynte is 6773 i i 1882 Its crystals are usually simpler than those of marcasite (Fig 48), though the number of planes observed in the species is larger. Most of the untwmned crystals
are a combination of oo P(no) with JP66 (014), or P 06 (on), or POO(IOI), and have a pris- matic habit. Twins are not rare The twinning plane is the same as in marcasite, and repetition is often met with The angle no/\i"io= 68° 13'
FIG 48-Arsenopynte Crystals with cop, The brachydomes are stri- no (m) , iP oo , 014 (M), and P 5 , on (j) ated horizontally, and often
the planes ooP(no) are stri- ated parallel to the edge oo P(no) A? (101)
The cleavage of arsenopynte is quite perfect parallel to ooP(no) The mineral is brittle and its fracture uneven Its hardness is 5 5-6 and density about 6 2 Its color is silver-white to steel-gray, its streak grayish black It is a good conductor of electricity
In the closed tube arsenopynte at first gives a red sublimate of AsS and then a black mirror of arsenic On charcoal it gives the usual reactions for sulphur and arsenic Cobaltiferous varieties react for cobalt with borax. The mineral yields sparks when struck wilh. steel and emits an arsenic smell It dissolves m nitric acid with the separa- tion of sulphur
Arsenopynte is distinguished from the cobalt sulphides and arsenides by the absence of Co
Synthesis — Crystals of the mineral are produced by heating in a closed tube at 300° precipitated FeAsS in a solution of NaHCO*
Occurrence — Arsenopynte crystals are often found disseminated through crystalline rocks, and often embedded m the gangue minerals of veins Like pyrite and marcasite they frequently fill vein fissures. Its associates are silver, tin and lead ores, chalcopyrite, pynte and sphalerite Localities — The mineral is abundant at Freiberg, m Saxony, at Tunaberg, in Sweden, and at Inquisivi Mt , Sorato, m Bolivia
It also occurs in fine crystals at Francoma in New Hampshire, at Blue Hill m Maine, at Chatham in Connecticut, and at St. Francois, Beauce Co, Quebec Massive arsenopynte is found near Kecscville
Sulphides, Tellurides Etc 113
Essex Co , near Edenville, Orange Co , and near Carmel, Putnam Co , N Y , and at Re\\ald, Flo\d Co , Va In most cases it is appaiently a result of pneumatoh sis
Uses — Arsenopynte was formerly the source of nearly all the arsenic of commerce The mineral is concentrated mechanical methods, and the concentrates are heated in retorts, when the following reaction takes place FeAsS FeS+As The arsenic being volatile is conducted into condensing chambers where it is collected When the mineral con- tains a reasonable amount of cobalt or of gold these metals are extracted
Uses of Arsenic — The metal arsenic has \ery little use in the arts, though its compounds find many applications as insecticides, medicines, pigments, in tanning, etc The basis of most of these is AsoOs, and this is produced directly from the fumes of smelters working on arsenical gold, silver and copper ores Only a portion of such fumes are saved, however, as even half of those produced at a single smelter center (Butte, Montana), would more than supply the entire demand of the United States for arsenic and its compounds Under these conditions the mining of arsenical pynte as a source of arsenic has ceased so far as the United States is concerned
Lollingite (FeAso) is usually massive, though its rare crystals are isomorphous in e\ery respect with those of arsenopynte The pure mineral is not common Most specimens are mixtures of lollmgite with arsenopynte or other sulphides or arsenides.
The mineral is silver-white or steel-gray Its streak is grayish black Its hardness is 5-5 5 and density about 72 It readily fuses to a mag- netic globule, at the same time evolving arsenic fumes It is soluble in HN03
It usually occurs in veins associated with other sulphides and arsen- ides It is found at Pans, Maine; at Edenville and Monroe, N. Y.; at vanous mines in North Carolina, and on Brush Creek, Gunnison Co., Colo At the last-named locality the mineral is in star-shaped crystalline aggregates, in twins and trillings, associated with siderite and barite.
Sylvanite Group
The sylvanite group includes at least three distinct minerals, all of which are ditellurides of gold or silver. The group is isodunorphous. The pure gold tellunde is known only in monochmc crystals, but the isomorphous mixtures of the gold and silver compounds occur both in monochmc and orthorhombic crystals
114 Descriptive Mineralogy
Orthorhombic bipyramidal Monoclmic prismatic
AuTeo Calavente
Krennente (Ag Au)Te2 Syhamte
All three minerals are utilized as ores of gold While occurring only in a few places, they are sufficiently abundant at some to be mined
Calaverite (AuTe2)
Calavente is a nearly pure gold chloride However, it is usually intermixed with small quantities of the silver tellunde An analysis of a specimen from Kalgoorhe, Australia, gave Te=5727, Au=4i 37,
Ag=58
Calaverite crystallizes m the monoclmic system (prismatic class) in crystals that are elongated parallel to the orthoaxis and deeply striated in this direction. Their axial ratio is i 6313 i ' i 1449 with £=90° 13' The prominent forms are ooP 66(100), ooPD(oio), oP(ooi), -Poc(ioi), +P6o(ioT), -2Poo(20i), +2P66(2oT), and P(in) Twinnmg is common and the resulting tuiins are very complicated Usually, however, the mineral occurs massive and granular
Calavente is opaque, silver-white or bronzy yellow in color and has a yellow-gray or greenish gray streak. Its surface is frequently covered with a yellow tarnish. The mineral is brittle and without distinct cleav- age Its hardness is 2-3 and density 9 04
On charcoal before the blowpipe the mineral fuses easily to a yellow globule of gold, yielding at the same tune the fumes of tellurium oxide. It dissolves in concentrated EfeSO.*, producing a deep red solution. When treated with HNOs it decomposes, leaving a rusty mass of spongy gold The solution treated with HC1 usually yields a slight precipitate of silver chloride
Calaverite is distinguished from most other minerals by the test for tellurium It is distinguished from fetzite (p 80), by its crystallization and the fact that it gives a yellow globule when roasted on charcoal, and from sylvamte by the small amount of silver it contains, its higher specific gravity, its color and its lack of cleavage It is distinguished from krennente by its crystallization
Occurrence — The mineral occurs in veins with the other tellurides associated with gold ores in Calaveras Co , Cal , and at the localities mentioned for petzite (see p 81) It is believed to have been deposited by pneumatolytic processes or by ascending magmatic water at com- paratively low temperatures.
Sulphides, Telluride8, Etc 115
Uses. — The mineral is mined with other tellundes in Boulder Co , and at Cripple Creek, Colorado, as an ore of gold
Sylvamte (Ag Au)Te2
Sylvamte is more common than calavente It is an isomorphous mixture of gold and silver tellundes in the ratio of about i . i Analyses follow
I Te=62 16 Au=24 45 Ag=i3 39 Total=ioo oo
II Te=59 78 Au=26 36 Ag i3 86 " ico oo
III Te=58 91 Au=29 35 Ag=n 74 100 oo
I Theoretical for AgTe2+ \uTe2 II and III Specimens trom Boulder Co , Colo
In crystallization the mineral is isomorphous with calavente, with an axial ratio a b . i 6339 i : i 1265 and $=90° 25' Its crystals are usually rich in planes, about 75 ha\mg been identified Their habit is usually tabular parallel to ooP ob (GIO), with this plane, —P 5c (101), oP(ooi), oo P 5b (100) and 2P2(T2i) predominating The mineral also occurs in skeleton crystals and in aggregates that are platy or granular Twinning is common, — P<X(IOI) the twinning plane Many twinned aggregates form networks suggesting writing, hence the name " Schnfterz '' often applied to the mineral by the Germans
Sylvamte is silver-white or steel-gray and has a brilliant metallic luster and a silver-white or yellowish gray streak Its hardness is between i and 2 and its densiU 7 9-8 3 Moreover, it possesses a per- fect cleavage parallel to oo P ob (oio)
Its chemical properties are the same as those of calavente, but the silver precipitate produced by adding HC1 to its solution m HNOs is always large It is best distinguished from the gold tellunde by its cleavage and from fetzite ((AgAuTe) and lessite (AgsTe) by its crystallization, and by the yellow metallic globule produced when the mineral is roasted on charcoal It is distinguishable from krennente by its crystallization
Localities and Origin — Sylvanite occurs with the other tellundes in veins at Offenbanya and Nagyag in Transylvania, at Cripple Creek and m Boulder Co , Colo , near Kalgoorhe, W Australia, in small quan- tities near Balmoral in the Black Hills, S D , and at Moss, near Thunder Bay, Ontano Like calavente it TV as deposited by magmatic water, or by hot vapors
Uses — It is mined with calaverite as a gold and silver ore at Cripple Creek and in Boulder Co , Colo.
Chapter V The Sulpho-Salts And Sulpho-Ferrites
THE sulpho-salts are salts of acids analogous to arsenic acid, and arsenious acid, HsAsOs, and the corresponding antimony acids HsSb04 and EfeSbOs The sulpho-acids differ from the arsenic and the antimony acids in containing sulphur in place of oxygen, thus HsAsS-i, HsAsSa, H3SbS4 and H3SbS3. The mineral enargite may be regarded as a salt of sulpharsenic acid, thus CusAsS-i, copper having replaced the hydrogen of the acid Proustite, on the other hand, is AgsAsSs, or a salt of sulpharsemous acid. The salts of sulpharsenic acid are called sulpharsenates, while those derived from sulpharsemous acid are known as sulpharsemtes The sulpharsenates are not represented among the commoner minerals, although the copper salt enargite is abundant at a few places A number of salts of other sulphur-arsenic acids are known but they are comparatively rare
There is another class of compounds with compositions analogous to those of the sulpho-salts, though their chemical nature is not well understood This is the group of the sulpho-ferntes We know that certain hydro-sides of iron may act as acids under certain conditions The sulpho-ferrites may be looked upon as salts of these acids in which, however, the oxygen has been replaced by sulphur, as in the case of the sulpho-acids referred to above Thus by replacement of 0 by S, m feme hydroxide Fe(OH)s the compound Fe(SH)s or HsFeSs results The salts of this acid are sulpho-ferrites This acid, by loss of HaS, may give rise to other acids in the same way that sulphuric acid (EfeSO/O, by loss of HaO, gives nse to pyrosulphuric acid In the case of the sulpho-acid we may have HsFeSs— H2S=HFeS2 The copper salt of this acid is the common mineral chalcopyrite, CuFeS2
The sulpho-salts are very numerous, but only a few of them are of sufficient importance to warrant a description in this book
Sulpho-Saltb And Sulpho-Ferrites 117
The Sulpharsenites And Sulphantimonites
The sulpharsemtes and sulphantimomtes are denvatives of the ortho acids HsAsSs and
Ortho Sulpho-Salts
The ortho salts are compounds in \\hich the hydrogen of the ortho acids is replaced by metals They include a large number of minerals, of which the following are the most important.
Boitrnomte (Cus Pb)s (SbSs)2 Orthorhombic
Pyrargynte AgsSbSa Hexagonal
Proustite AgsAsSs Hexagonal
PYRARGYRITE GROUP Pyrargynte (AgsSbSs)
Pyrargyrite, or dark ruby silver, is an important silver ore, especially in Mexico, Chile and the \\estern United States. The name ruby silver is given to it because thin splinters transmit deep red light The mineral is usually mixed with other ores in compact masses, but it also forms handsome crystals
The composition of pyrargyrite is represented by the formula AggSbSs which demands 17 82 per cent S , 22 21 per cent Sb , 59 97 per cent Ag Many specimens contain also a small quantity of arsenic, through the admixture of the isomorphous compound proustite The analyses given below show the effect of the intermixture of the two molecules
S Sb As Ag Total
Andreasberg, Harz 17 65 22 36 59 73 99 77
Zacatecas, Mexico 17 74 22 39 27 60 04 100 44
Freiberg, Saxony 17 95 18 58 2 62 60 63 99 78
The crystals of pyrargyrite are rhombohedral and hemunorphic (ditngonal pyramidal class), with an axial ratio i : 8038 They are usually quite complex and are often twinned. The species is very rich in forms, not less than 150 having been reported The most prominent of these are ooP2(ii2o), ooP(ioTo), R(ioli), -iR(oil2) and the scalenohedrons R3(2i3i) and iR3(2i34) (Fig 49) In the commonest twinning law the twinning plane is ooP2(ii2o) and the composition
118 Descriptive Mineralogy
face oPfooi) The c axes in the twinned portions are parallel and the o=P2(ii2~o) planes coincident, so that the at a hasty glance looks like a simple crystal The angle roll /\lioi 71° 22'
The cleavage of pyrargynte is distinct parallel to R(ioTi) Its frac- ture is conchoidal or une\ en The mineral is apparently opaque and its color is grayish black in reflected light, but is trans- parent or translucent and deep red in transmitted light Its streak is purplish red For lithium light 03=3084, €=2881 It is not an electrical conductor
In the closed tube the mineral fuses easily and
/
ghes a reddish sublimate When heated
sodium carbonate on charcoal it is reduced to a
P\rag\nte with g°bule of silver, \which, when dissolved in nitric
1 1 20 (a) acid, yields a silver chloride precipitate when
I treated a soluble chloride The mineral dis-
solves in nitric acid with the separation of sulphur and a white precipitate of antimony oxide It is also soluble in a strong solution of KOH From this solution HC1 precipitates orange Sb2Ss (compare proustite)
The color and streak of p>rargynte, together with its translucency, distinguish it from nearly all other minerals Its reaction for silver serves to distinguish it from cuprite, dnnalar and realgar, which it some- times resembles The distinction between this mineral and its iso- morph, proustite, is based on the streak and the reaction for anti- mony.
Pyrargynte occurs as a pseudomorph after native silver. On the other hand it is occasionally altered to pynte or argentite, and some- times to silver
Syntheses — Microscopic crystals ha\e been made by heating in a porcelain tube, metallic silver and antimony chlorides in a current of IfeS, and by the action of the same gas at a red heat on a mixture of metallic silver and melted antimony* o\ide
Occurrence, Localities and Origin — Pyrargynte occurs in veins asso- ciated with other compounds of silver and scmetimes with galena and arsenic It is most common in the zone of secondary enrichment of silver veins. The crystallized variety is found at Andreasberg in the Harz, at Freiberg, in Saxony, at Pnbram, in Bohemia, at many places in Hungary, and at Chanarcillo, in Chile The massive variety is worked as an ore of silver at Guanajuato in Mexico and in several of the western states, as, for instance in the Ruby district, Gunmson Co , and in other
Sulpho-Salts And Sulpho-Ferrites 119
mining districts m Colorado, near Washoe and Austin, Nevada, and at several points in Idaho, Ne\v Mexico, Utah and Arizona
Uses — The mineral is an important ore of silver in Mexico and in the western United States It is usually associated with other sulphur- bearing ores of sil\er, the metal being extracted from the mixture by the processes referred to under argentite,
Proustite (AgsAsSs)
Proustite, or light ruby siher, is isomorphous with p\rargynte It differs from the latter mineral in containing arsenic m place of antimony It occurs both massive and in crystals, and like pyrargynte is an ore of silver
The formula abo\e given demands 19 43 per cent S, 15 17 per cent As, and 65 40 per cent sih er The analysis of a specimen from Mexico yields figures that correspond \ery nearly to these Cr}stals from Chanarcillo contain a slight admixture of the antimony compound
S As Sb Ag Total
Mexico 19 52 14 98 65 39 99 89
Chanarcillo, Chile 19 64 13 85 i 41 65 06 99 96
Like pyrargynte, proustite is rhombohedral Its crystals are pris- matic or acute rhombohedral The forms present on them are much less numerous than those on the corresponding antimony compound, the predominant ones being ocp2(ii2o), iR(ioT4), -iR(oil2), Rd(2i3i), ~|R4(3557J and other scalenohedrons (see Fig 50) Twins are common, the t winning planes being (i), parallel to JR(iol4) and (2) parallel to R(ioTi) The angle io7i Alici 7i° 12'. FlG So-Crystal of
The cleavage, fracture and haidness of prous- JJJHJ Jj tite are the same as for pyrargynte Its hard- (j/) and -|R, 0112 ness is 2 and its density is about 5.6 The mineral is transparent or translucent Its color is grayish black by reflected light and scarlet m transparent pieces by transmitted light. Under the long-continued influence of daylight the color deepens until it becomes darker than that of pyrargynte Its streak is cirnabar-red to brownish black Its luster is adamantine. It is a nonconductor of electncity For sodium light 03=3 0877, 2 7924
In the closed tube proustite fuses easily and gives a slight sublimate
120 Descriptive Mineralogy
of \\hite arsenic oxide In its other chemical properties it resembles pyrargyrite except that it gi\es reactions for arsenic \\here this mineral reacts for antimony, and yields onh sulphur dissohed in HNOa From its solution in KOH a yellow precipitate of AsSs is thrown upon the addition of HC1 (compare pyrargyrite)
Proustite differs from pyra g \nte in Us color, transparency and streak, as \vell as in its arsenic reactions It is distinguished from cinnabar and cuprite (CuO) the arsenic test
Syntheses — Crystals of proustite ha\e been produced by reactions analogous to those that yield p\rargynte, when arsenic compounds are employed in place of antimon\ compounds
Occurrence — The mineral occurs under the same conditions and with the same associates as pyrargyrite and it yields the same alteration products as pyrargynte
Localities and Uses — Handsome crystals of proustite occur at Freiberg and other places in Saxony, at Wolfach in Baden, at Markirchen in Alsace and at Chanarcillo in Chile It is associated with pyrargyrite and with other ores of silver
In the western United States it is quite abundant, more particular!} in the Ruby district, Colorado, at Poorman lode in Idaho, and in all other localities where pyrargynte occurs In many it is mined as an ore of silver
Bournonite ((Pb Cu2)3(SbS3)2)
Bournomte is a comparatively rare mineral It occurs either in compact or granular masses or in well developed crystals of a steel gray color It is not of any economic importance except as it may be mixed with other copper compounds exploited for copper
Analyses of bournomte from two localities are given below
S Sb
I- 19 36 23 57 n. 19 78 23 80
I Liskeard, Cornwall, England II Felsobinya, Hungary
These analyses are by no means accurate, but they show the compo- sition of the mineral to be approximately Pb, Cu, Sb and S, in which the elements are combined in the following proportions 8=19 8 per cent, Sb=24 7 per cent, Pb 42 5 per cent, Cu 13 per cent
Bournonite crystals are orthorhombic (rhombic bipyramidal class),
As
Pb
Cu
Fe
Total
Sulpho-Salts Axd 3Ulphoferrites
with a . b 9380 i 8969 They are usually tabular 'Fig 51;, or short, prismatic in habit, and are often in repeated twins fFig 52*, with wheel-shaped or cross-like forms The principal planes observed on them are oP(ooi),P<(ioij, POD (011 ),iP(ii2), wP(noi, xPxiioo, and oo P oc (oio), though 90 or more planes are n The most com- mon twinning plane is oo P(no) Angle IIOAIIO— 86° 20'
The luster of the mineral is brilliant metallic Its and streak are steel-gray Its cleavage is imperfect, parallel to QC P c£ f oio; and its fracture conchoidal or uneven Its hardness is 2 5-3 and density 5 8 Like most other metallic minerals it is opaque It is a ery poor con- ductor of electricity
In the closed tube bournomte decrepitates and yields a dark red sub- limate In the open tube, and on charcoal, it gives reactions for Sb, S, Pb and Cu When treated with nitric acid it decomposes, producing a
FIG 51 FIG s-
FIG 51 — Bournomte Crystal \uth oP ooi (c], P 55 , 101 (0), 112 fu) and P x,
on in)
FIG 52 — Bournonite Fourlmg Tuinned about x P, no (m) Form c same as in Fig 51 b P oo (oio; and a oc P 55 s 100)
blue solution of copper nitrate that turns to an intense azure blue when an excess of ammonia is added In this solution is a residue of sulphur and a white precipitate that contains lead and antimon\ .
Bournomte is distinguished from most other minerals by its reactions for both antimony and sulphur. From other sulphantunonites it is distinguished by its color, hardness and density.
On long exposure to the atmosphere bournomte alters to the car- bonates of lead (cerussite and copper (malachite and azunte)
Synthesis — Crystals of bournomte have been obtained by the action of gaseous HkS on the chlorides and oxides of Pb, Cu and Sb, at moderate temperatures
Occurrence — The mineral occurs principally in veins with galena, sphalerite, stibmte, chalcopynte and tetrahednte
Localities. — Good crystals are found in the mines at Neudorf, Harz; at Pnbram, m Bohemia, at Felsobanya, Kapnik and other places in Hungary, and at various places in Chile. In North America it has
122 Descriptive Mineralogy
been found at the Boggs Mine in Yavapai Co , Ariz , in Montgomery Co , Ark , and at Marmora, Hastings Co , and Darling, Lanark Co , Ontario.
The Sulphdiarsenites And Sulphdiantimonites
A large number of sulpho-salts are apparent!} salts of acids that contain two or more atoms of As or Sb in the molecule These acids may be regarded as derived from the ortho aads by the abstraction of HsS, thus The arsemous acid containing two atoms of As may be thought of as 2H3AsS3-H2S=H4As2S5 Acids with larger proportions of arsenic may be regarded as derived in a similar manner from three or more molecules of the ortho acid Only a few of these salts are common as minerals. Among the more common are two that are lead salts of derivatives of sulpharsemous and sulphantimonous acids,
Jamesomte (PbsSbgSs) and Dufrenoysite (Pb2AsgS5)
Jamesonite and dufrenoysite are lead salts of the acids H4Sb2Ss and H4As2Ss Both minerals occur in acicular and columnar orthorhombic crystals and in fibrous and compact masses of lead-gray color Their cleavage is parallel to the base The minerals are brittle and have an uneven to conchoidal fracture Their hardness is 2-3 and density 5 5-6 The streak of jamesomte is grayish black, and of dufreynosite reddish brown. Both minerals are easily fusible They are soluble in HC1 with the evolution of EfeS, giving a solution from which acicular crystals of PbCfe separate on cooling They are decomposed by HNOs, with the separation of a white basic lead salt They are found in veins with antimony and sulphide ores abroad and at several points in Nevada and in the antimony mines in Sevier Co , Arkansas
The Sdlpharsewates And Sdlphantimoitates
The sulpharsenates are salts of sulpharsenic acid, HaAsS and the sulphantimonates, the salts of the corresponding antimony acid, HsSbS These compounds are much less numerous among the minerals than the sulpharsenites and sulphantimomtes. Moreover, no member of the former groups is as common as several of the members of the latter The most important member is the mineral enargite (CusAsS an ortho- sulpharsenate, which in a few places is wrought as a copper ore.
Sulpho-Salts And Sulpho-Ferrites 123
Enargite
Enargite, though a rare mineral, is so abundant at a few points that it has been mined as an ore of copper
Theoretically, the mineral is 8=326, As=i9i, 01=483 Most specimens, however, contain an admixture of the isomorphous anti- mony compound, jamaiimte and consequently sho\v the presence of antimony. A specimen from the Rarus Mine, Butte, Montana, yielded
S As Sb Cu Fe Zn Ins Total
31 44 17 91 i 76 48 67 .33 10 ii 100 32
The mineral crystallizes in the orthorhombic system (bipyramidal class), m crystals with an axial ratio 8694 : i : 8308 Their habit is usually prismatic, and they are strongly striated vertically. The crystals are usually highly modi- fied, with the following forms predominating oo P 06(100), ooP(no), ooP3(i2o), ooPfo), oo P 06 (oio), and oP(ooi) (Fig 53) Stellar trill- ings, with ooP2(i2o) the twinning plane, have a pseudohexagonal habit. The mineral occurs also
in columnar and platy masses FIG _Enarglte Crys_
Enargite possesses a perfect prismatic cleavage tal wth M Pj 1IO (m and an uneven fracture. It is opaque with a OOP 55,100 (a), grayish black color and streak. Its hardness is 3 i2o(A)andoP,oor(c). and density 44. It is a poor electrical conductor.
It is easily fusible before the blowpipe When roasted on charcoal it gives the reactions for S and As, and the roasted residue when moistened with HC1 imparts to the flame the azure-blue color char- acteristic of copper. In the closed tube it decrepitates and gives a sublimate of S. When heated to fusion it yields a sublimate of arsenic sulphide The mineral is soluble in aqua regia
Enargite is easily recognized by its crystallization and blowpipe reactions
Occuiience. — Enargite is associated with other copper ores in veins filled by magmatiC water at intermediate depths and in a few replace- ment deposits
Localities — Although not widely distributed, enargite occurs in large quantities in the copper mines near Morococha, Peru; Copiap6, Chile; in the province of La Rioja, Argentine; on Luzon, Philippine Islands,
124 Descriptive Mineralogy
and in the United States, at Butte, Montana in the San Juan Moun- tains, Colorado and m the Tmtic District, Utah
Uses —It is smelted as an ore of copper At the Butte smelter it furnishes the arsenic that is separated from the smelter fumes and placed upon the market as arsenic oxide (see p 113)
The Basic Sulpho-Salts
The basic sulpho-salts are compounds in \\hich there is a greater percentage of the basic elements (metals, etc), present than is necessary to replace all the hydrogen of the ortho acids Thus, the copper orthosulpharsenate, enargite, is CusAsSU The mineral steph- anite is AgsSbS* and the pure silver polybasite AggSbSe
Since three atoms of Ag are sufficient to replace all the hydrogen atoms m the normal acid containing one atom of antimony and the quantities of silver present in stephamte and polybasite are in excess of this requirement, the two minerals are described as basic The exact relations of the atoms to one another in the molecules are not known
Although the number of basic sulpho-salts occurring as minerals is large only four are common These are:
Stephamte AgoSbS* Orthorhombic
Polybasite (Ag - CuSbSc Monoclimc
Tetrahednte (R")4Sb2S7 Isometric
T&nnantite (R'AsoS? Isometric
Stephanite (Ag5SbS4)
Stephanite, though a comparatively rare mineral, is an important ore of silver in some camps It occurs massive, in disseminated grains and as aggregates of small crystals Analyses indicate a composition very dose to the requirements of the formula AgsSbS4
S Sb Ag AsandCu Total
Theoretical . . . 16 28 15 22 68 50 100 oo
Crystals, Chanarollo, Chile 16 02 15 22 68 65 tr 99 89
Stephanite crystallizes in hemimorphic orthorhombic crystals (rhom- bic pyramidal class), with an axial ratio .6291 : i : .6851. The crystals are highly modified, 125 forms having been identified upon them. They have usually the habit of hexagonal prisms, their predominant planes
Sulpho-Salts And Sulpho-Ferrites 125
being ooP(no) and oop 06(010), terminated by oP(ooi), P(in) and 2Poc (021) at one or the other end of the c aus (Fig 54) Twins are common, with oo P(no) and oP(ooi) the inning planes
The mineral is black and opaque and its streak is black Its hard- ness is 2 and density 2 — 63 It cleaves parallel to oo P 06 (oio) has an uneven frac- ture, and is a poor conductor of electricity
On charcoal stephamte fuses \ery easily to a dark gray globule, at the same time yielding the \white fumes of antimony oxide FIG. 54 —Stephanite Crystal and the pungent odor of S02 Under the oP, oox reducing flame the globule is reduced to oio(ft) ooP, !io W, |P,
,, , m-, i T t - S32 (P)> "°° °21 W-
metallic silver. The mineral dissolves in
dilute nitric acid and this solution gives a white precipitate with HC1.
Stephamte is easily distinguished from other black minerals by its easy fusibility, its crystallization, and its reactions for Ag, Sb and S
Localities — The mineral is associated Tvith other silver ores in the zone of secondary enrichment of veins at Freiberg, Saxony, Joachimsthal and Pribram, Bohemia, the Comstock Lode and other mines in the Rocky Mountain region and at many points in Mexico and Peru.
Uses — It is mined together with other compounds as an ore of silver It is particularly abundant in the ores of the Comstock Lode, Nev., and of the Las Chispas Mine, Sonora, Mex.
Polybasite ((Ag-Cu)9SbS6)
Polybasite is the name usually applied to the mixture of basic sulph- aifomtes and sulpharsemtes of the general formula RSb-AsJSe, in which R'= Ag and Cu. More properly the name is applied to the anti- monite, and the corresponding arsenite is designated as pearceite. Sev- eral typical analyses follow
S As Sb Ag Cu Fe Pb Ins Total
I 17 46 7 56 . . 59 22 15 65 - 99 89
H- 17 7i 7 39 SS-I7 ii i 05 42 99 85
Hi. 15 43 5° 10.64 68 39 $ 13 . . 100 09
IV. 16 37 3 88 5 is 6793 607 . .76 ... 100.18
I Pearceite Veta Rica Mine, Sierra Mojada, Mexico II. Crystals of pearceite, Drumlummon Mine, Marysville, Montana.
III. Polybasite, Santa Lucia Mine, Guanajuato, Mexico
IV. Polybasite, Quespisiza, Clule
126 Descriptive Mixeralogy
The crystallization of the two minerals, which are completely isomor- phous, is monoclinic (prismatic class) Their axial ratios are
Pearceite, a : b : 1.7309 : i : i 6199 £=9°° 9' Polybasite, 7309 : i : i 5796 £=90'
Y
o
The crystals are commonly tabular or prismatic, with a distinct hexagonal habit. The prominent forms are oP(ooi), P(ni) and 2P 55 (20!). Contact twinning is common, with oo P(no) the twinning plane, and oP(ooT) the composition plane
Both minerals are nearly opaque Except in very thin splinters they are steel-gray to iron-black in color Very thin plates are trans- lucsnt and cherry-red Their streaks are black Their cleavage is perfect parallel to oP(ooi) and their fracture uneven Their hardness is 2-3, and density 6-6 2
Both minerals are easily fusible They usually exhibit the reactions for Ag, Sb, As and S
They are readily distinguished from all other minerals but silver sulpho-salts by their blowpipe reactions From these they are distin- guished by their crystallization Pearceite and polybasite are distin- guished from one another by the relative quantities of As and Sb they contain
Occurrence — Both minerals occur in the zone of secondary enrich- ment in veins of silver sulphides.
Localities — Polybasite was an important ore of silver in the Comstock Lode, Nevada It is at present mined with other silver ores at Ouray, Colorado, at Marysville, Montana, at Guanajuato, Mexico, and at various points in Chile Good crystals occur at Freiberg, Saxony, at Joachimsthal, Bohemia, and in the mines in Colorado, Mexico and Chile.
Tetrahedrite Group
The name tetrahedrite is given to a mixture of basic sulphanti- monites and sulpharsenites crystallizing together in isometric forms with a distinct tetrahedral habit (hextetrahedral dass) The isomorphism is so complete that all gradations between the various members of the group are frequently met with The arsenic-bearing member of the series is known as tennantite and the corresponding antimony member as letrakednte The latter is the more common
The following six analyses of tetrahedrite will give some idea of the great range in composition observed in the species.
SULPHO-SALTS AND St'LPHO-FERRITES 127
S Sb As Cu Fe Zn Ag Hg Pb Total
I 27 60 25 87 tr 35 85 2 66 5 15 2 30 99 43
II 23 51 17 21 7 67 42 oo 8 28 49 55 99 71
Iii. 24 44 27 60 27 41 4 27 2 31 14 54 . 100 57
IV 24 89 30 18 tr 32 80 5 85 07 5 57 99 36
V 21 67 24 72 33 53 56 i So 16 23 98 51
I Xewbur>port, Mass
II Cajabamba, Peru
HI Star City, Xev
IV Poracs, Hungary.
V Arizona.
Upon examination these are found to correspond approximately to the formula R' SbaS:, in which the R" is Cu2, Pb, Fe, Zn, Hg, Ag2 and sometimes Co and Ni When R is replaced entirely by copper, the formula (CusSb2S-) demands 23 i per cent S, 24 8 per cent Sb and 52 i per cent Cu
Analyses of tennantite yield analogous results that may be repre- sented by the formula CusAs2Sr which demands 26 6 per cent S, 20 76 per cent As and 52 64 per cent Cu
Analyses of even the best crystallized specimens rarely yield As or Sb alone. Moreover, nearly all show the presence of Zn in notable quantity The great variation noted in the composition of different specimens which appear to be pure crystals has led to the proposal of other formulas than those given abo\e — some being simpler and others more complex It is possible that the variation may be explained as due, in part, to some kind of solid solution, rather than as the result solely of isomorph'jus replacement It is more probable, however, that it is due to the intergrowth of notable quantities of various sulphides with the sulpho-salts
There is still considerable confusion in the proper naming of the mem- bers of the series, but generally the forms composed predominantly of Cu, Sb and S with or without Zn are known as tetrahednte and those containing As m place of Sb as tennantite, although several authors confine the use of the latter term to arsenical tetrahedrites containing a notable quantity of iron
Since the members of the tetrahedrite series often contain a large quantity of metals other than Cu and Zn the group has been so sub- divided as to indicate this fact Thus, there are argentiferous, mercurial and plumbiferous varieties of tetrahedrite Some of these varieties are utilized as ores of the metals that replace the copper and zinc in the more
128 Descriptive Mineralogy
common varieties The relations of the ordinary (II) and the bis- muthiferous tennantites (III) to tetrahednte (I) are shown by the fol- lowing three analyses.
S As Sb Bi Cu Fe Ag Pb Co Total
I 24 48 tr 28 85 45 39 i " IQo 15
II 26 61 19 03 51 62 i 95 99 21
III 29 10 ii 44 2 19 13 07 37 52 6 51 04 i 20 101 07
I Fresney d'Oisans, France. II Cornwall, England. Ill Cremenz, Switzerland
The crystals of both tetrahedrite and tennantite are tetrahedral in habit, the principal forms on them consisting of the simple tetrahedron
and complex tetrahedrons such as —(211), — — (332) together with
the dodecahedron, ooQ(iio) and the cube, ooOoo(ioo) (Fig. 55) Twins are common with 0(in) the twinning plane. These are sometimes contact twins and sometimes interpenetration twins. Some crystals are very complicated, because of the presence on them of a great number of forms The total number of distinct forms that have been identified is about 90. The mineral
m L j occurs also in granular, dense and earthy FIG 55 —Tetrahednte Crys- 6 ' J
o masses.
tal with -, 1 1 1 W , o, The fracture of the tetrahedrites is uneven
no (d) and fO, 332 Their hardness varies between 3 and 4 5 and
their density between 4 4 and 5 i Their color
is between dark gray and iron-black, except in thin splinters, which sometimes exhibit a cherry-red translucency. Their streak is like their color. All tetrahedrites are thermo-electric.
The chemical properties of the different varieties of tetrahedntes vary with the constituents present. All give tests for sulphur and for either antimony or arsenic, and all show the presence of copper in a borax bead. The reactions of other metals that may be present may be learned by consulting pages 483-494.
The crystals of tetrahedrite are so characteristic that there is little danger of confusing the crystallized mineral with other minerals of the same color. The massive forms resemble most dearly arseno$yritey lownmtie and chalcocite From these the tetrahedrites are
Sulpho-Salts And Sulpho-Ferrites 129
best distinguished by their hardness, together with their blowpipe reac- tions
Tetrahednte appears to suffer alteration quite readily, since pseudo- morphs of several carbonates and sulphides after tetrahednte crystals are well known
Synthesis — Crystals of the tetrahedrites have been made by passing the vapors of the chlorides of the metals and the chlorides of arsenic or antimony and EfeS through red-hot porcelain tubes They have also been observed in Roman coins that had Iain for a long time in the hot springs of Bourbonne-les-Bains, Haute-Marne, France.
Occurrence — The tetrahedrites are very common in the zone of secondary enrichment of sulphide veins and in impregnations They occur associated with chalcopyrite, pynte, sphalerite, galena and other silver, lead and copper ores in nearly all regions where the sulphide ores of these metals are found They occur also as primary constituents of veins of silver ores, where they were deposited by magmatic waters.
Localities — In the United States tetrahedrite occurs at the Kellogg Mines, ten miles north of Little Rock, Arkansas, near Central City and at Georgetown, Colorado; in the Ruby and other mining districts in the same State; at the De Soto Mine in Humboldt Co , Nevada, and at several places in Montana, Utah and Arizona It is found also in British Columbia and in Mexico, and at Broken Hill, New South Wales
The arsenical tetrahedrites are not quite as common as is the anti- monial variety Excellent crystals occur in the Cornish Mines, at Freiberg in Saxony, at Skutterud in Norway, and at Capelton, Quebec
Uses. — The mineral is used to some extent as an ore of silver or of copper, the separation of the metals being effected in the same way as in the case of the sulphides of these substances.
The Sulpho-Ferrites
Only two sulpho-f emtes are sufficiently important to merit descrip- tion here Both of these are copper compounds and both are used as ores of this metal, one — chalcopyrite — being one of the most important ores of the metal at present worked
The first of these minerals discussed, bornite, is a basic salt of the acid EfeFeSa, the second is the salt of the derived acid HFeS2, which may be regarded as the normal acid from which one molecule of H2S has been abstracted (see p. n6],
130 . Descriptive Mineralogy
Bornite (Cu5FeS4)
Bormte, known also as horseflesh ore because of its peculiar purplish- red color, is found usually massive In Montana and in Chile it con- stitutes an important ore of copper
Bornite is probably a basic sulpho-femte, though analyses yield lesults that vary quite widely, especially in the case of massive varieties This variation is due to the greater or less admixture of copper sulphides, mainly chalcocite, with the bormte The theoretical composition of the mineral is 25 55 S, 63 27 Cu, and 11.18 Fe The analyses of a crystallized variety from Bristol, Conn , and of a massive variety from the Bruce Mines, Ontano, follow.
S Cu Fe Ins Total
Bristol, Conn . 25 54 63 24 n 20 99 98
Bruce Mines, Ont 25 39 62 78 n 28 30 99 75
The crystallization of bormte is isometric (hexoctahedral class), in combinations of oo O oo (ico), oo 0(iio),0(rn), and sometimes 202(211) Crystals often form mterpenetration twins, with 0 the twinning plane
The fracture of the mineral is conchoidal, its hardness 3 and density about 5 On fresh fracture the color varies from a copper-red to a pur- plish brown Upon exposure alteration rapidly takes place covering the mineral with an iridescent purple tarnish. Its streak is grayish black It is a good conductor of electricity
Chemically, the mineral possesses no characteristics other than those to be expected from a compound of iron, copper and sulphur It dis- solves in nitric acid with the separation of sulphur
It is easily recognized by its purplish brown color on fresh fractures and its purple tarnish.
Bornite alters to chalcopyrite, chalcocite. covellite, cuprite (CuaO), chrysocolla (CuSiQs 2H20) and the carbonates, malachite and azurite. On the other hand, bornite pseudomorphs after chalcopyrite and chal- cocite are not uncommon
Syntheses — Roman copper coins found immersed in the water of warm springs in France have been partly changed to bornite. Crystals have been formed by the action of EkS at a comparatively low tempera- ture (ioo°-2oo° C ), upon a mixture of CuaO, CuO and Fe20s
Occurrence and Origin — Bornite is usually associated with other copper ores in veins and lodes, where it is in some cases a primary min- eral deposited by magmatic waters and in others a secondary mineral produced in the zone of enrichment of sulphide veins. It also sometimes
Sulpho-Salts And Sulpho-Ferrites 131
impregnates sedimentary rocks, where its origin is part due to contact action.
Localities — The crystallized mineral occurs near Redruth, Cornwall Eng , and at Bristol, Conn The massive mineral is found at many places in Norway and Sweden It is the principal ore of some of the Bolivian, Chilian, Peruvian and Mexican mines and of the Canadian mines near Quebec In the United States it has been mined at Bristol, Conn , and at Butte, Montana
Uses — Bornite is mined with chalcopyrite and other copper com- pounds as an ore of this metal
Chalcopynte (CuFeS2)
From an economic point of this mineral is the most important of the sulpho-salts, as it is one of the most important ores of copper
Fig 56 Fig 57 Fig 58
FIG. 56 —Chalcopynte Crystal with P, in (p), -P, ill (p) and 2? , 201 (3).
IP Pz
FEG 57 — Chalcopynte Crystal with — , 772 (&J and — , 212 (x) The form
sometimes approaches P(zio) and x approaches P (xoi1) FIG 58 — Chalcopynte Twinned about P(iu)
known. It occurs both massive and crystallized. From its similarity to pyrite in appearance it is often known as copper pyrites.
Crystallized specimens of chalcopyrite contain 35 per cent S, 34 5 per cent Cu and 30.5 per cent Fe, corresponding to the formula CuFeSk, i e , a copper salt of the acid HFeS2 The mineral often contains small quantities of intermixed pyrite. It also contains in some instances selenium, thallium, gold and silver
The crystallization of chalcopynte is in the sphenoidal, hemihedral division of the tetragonal system (tetragonal scalenohedron class).
132 Descriptive Mineralogy
P The crystals are usually sphenoidal in habit with the sphenoids -(in),
3p
and —(332) the predominant forms (Figs 56 and 57) In addition to
these there are often present also oo P oo (100), oo P(no), 2? oo (201),
ff and a very acute sphenoid that is approximately — (772), supposed to be
p
due to the oscillation of oo P(no) and -(in) (Fig 57) Twins are quite
common, with the twinning plane parallel to P (Fig 58). The plus faces of the sphenoid are often rough and striated, while the minus faces are smooth and even.
The fracture of the mineral is uneven. Its hardness is 3 5-4 and density about 4.2. Its luster is metallic and color brass-yellow Old fracture surfaces are often tarnished with an iridescent coating Its streak is greenish black. It is an excellent conductor of electricity
On charcoal the mineral melts to a magnetic globule. When mixed with Na2COs and fused on charcoal, a copper globule containing iron results. When treated with nitric aad it dissolves, forming a green solution in which float spongy masses of sulphur The addition of ammonia to the solution changes it to a deep blue color and at the same time causes a precipitate of red feme hydroxide.
From the few brassy colored minerals that resemble it, chalcopyrite is distinguished by its hardness and streak.
When subjected to the action of the atmosphere or to percolating atmospheric water chalcopyrite loses its iron component and changes to covelhte and chalcocite The iron passes into limomte. Bornite, copper and pyrite are also frequent products of its alteration. In the oxidation zone of veins it yields limonite, the carbonates, malachite and azurite, and cuprite (Cu20). When exposed to the leaching action of water, limonite alone may remain to mark the outcrop of veins, the copper being carried downward in solution to enrich the lower portions of the vein. The deposit of limonite on the surface is known as
Syntheses — Crystals of chalcopyrite have been produced by the action of HaS upon a moderately heated mixture of CuO and FOs cndosed in a glass tube. The mineral has also been made by the action of warm spring waters upon ancient copper coins. It is also a fairly common product of roasting-oven operations
Occurrence and Origin.— Chalcopyrite is widely disseminated as a primary vein mineral, and is often found in nests in crystalline rocks.
Sulpho-Salts And Sulpho-Ferrites 133
It also impregnates slates and other sedimentary rocks, schists and altered igneous rocks where, in some cases, it is a contact deposit and in others is original It is also formed by secondary processes caus- ing enrichment of copper sulphide veins Its most common associ- ates are galena, sphalerite and pyrite. It is the principal copper ore m the Cornwall mines, where it is associated with cassitente (Sn02), galena and other sulphides. It is also the important copper ore of the deposits of Falun, Sweden, of Namaqualand in South Africa, those near Copiapo in Chile, those of Mansfeld, Germany, of the Rio Tinto district in Spain, of Butte and other places in Montana, and of the great copper-producing districts in Arizona, Utah and Nevada.
Crystals occur near Rossie, Wurtzboro and Edenville, N. Y., at the French Creek Mines, Chester Co., Penn., near Finksburg, Md., and at many other places
Extraction — The mineral is concentrated by mechanical methods. The concentrates are roasted at a moderately high temperature, the iron being transformed into oxides and the copper partly into oxide and partly into sulphide. Upon further heating with a flux the iron oxide unites with this to form a slag and the copper sulphide melts, and collects at the bottom of the furnace as " matte/' which consists of mixed copper and copper sulphide. This is roasted in a current of air to free it from sulphur. By this process all of the copper is transformed into the oxide, which may be converted into the metal by reduction. The metal is finally refined by electrical processes. Much of the copper obtained from chalcopyrite contains silver or gold, or both, which may be recov- ered by any one of several processes.
Uses.— A large portion of the copper produced in the world is obtained by the smelting of chalcopyrite and the ores associated with it.
Production.— The world's total product of copper has been referred to in another place (p. 55). Of this total (2,251,300,000 Ib.) the United States supplied, in 1912, 1,243,300,000 Ib., of which about 1,000,000,000 Ib. were obtained from sulphide ores. Arizona and Montana produced the greater portion of this large quantity, the former contributing about 359,000,000 Ib. to the aggregate, and the latter 308,800,000 Ib Out- side of the United States the most important copper-producing countries are Mexico, Japan, Spain and Portugal, Australia, Chile, Canada, Russia, Peru and Germany, in the order named. Practically all of this copper, except that from Japan and Mexico, is extracted from sulphide ores.
Chapter Vi
The Chlorides Bromides Iodides \Nd Fluorides
THE salts belonging to this group are 'compounds of metals with hydrochloric (HC1), h>drobromic (HBr), hydnodic (HI) and hydro- fluoric (HF) acids Only a few are of importance Of these some are simple chlorides, others are simple fluorides, others are double chlorides or fluorides (i e cryolite, AlFaNaF), and others are double hydrox- ides and chlorides (atacamite)
The Chlorides
The simple chlorides crystallize in the isometric system, but in differ- ent classes in this system. They comprise salts of the alkalies, K, Na and NKi, and of silver Of these only three mmerals are of importance, viz.: sylmte, hahte and cerargynte
Halite (Had)
Halite, or common salt, is the best known and most abundant of the native chlorides It is a colorless, transparent mineral occurring in crystals, and in granular and compact masses
Pure halite consists of 39 4 per cent Cl and 60 6 per cent Na The mineral usually contains as impurities clay, sulphates and organic substances The several analyses quoted below indicate the nature of the commonest impurities and their abundance in typical specimens
NaCl CaCl MgCl CaS04 Na2S04 Mg2S04 Clay H20
I 97 35 ... i 01 43 23 30
II. 90 3 „ . 5 oo 2 oo 2 oo 70
III, 98 88 tr tr .79 33
I Stassfurt, Germany. II Vic, France III. Petit Anse, La.
The crystallization of halite is isometric (hexoctahedral class), the principal forms being ooOoo(ioo), 0(iu) and ooO(no) Often the
Chlorides, Fluorides, Etc 135
faces of the forms are hollowed or depressed giving nse to what are called " hopper crystals " (Fig 59). The mineral occurs also in coarse, gran- ular aggregates, in lamellar and fibrous masses and in stalactites
Its cleavage is perfect parallel to oo 0 oo (100) Its fracture is con- choidal Its hardness is 2-2 5 and density about 217 Halite, when pure, is colorless, but the impurities present often color it red, gray, yellow or blue The bright blue motthngs obsened in many specimens are thought to be due to the presence of colloidal sodium. The mineral is transparent or translucent and its luster is \itreous. Its streak is colorless Its saline taste is well known. It is diathermous and is a nonconductor of electricity. prG 59— Hopper- The mineral is plastic under pressure and its plasticity Shaped Cube of increases with the temperature Its index of refraction Halite for sodium light, i 5442
In the closed tube halite fuses and often it decrepitates. When heated before the blowpipe it fuses (at 776°) and colors the flame yellow. The chlorine reaction is easily obtained by adding a small particle cf the mineral to a microcosmic salt bead that has been saturated with copper oxide. This, when heated before the blowpipe, colors the flame a bnl- hant blue. The mineral easily dissolves in water, and its solution yields an abundant white precipitate with silver nitrate.
The solubility of halite is accountable for a large number of pseudomorphs. The crystals embedded in clays are gradually dissolved, leaving a mold that may be filled by other substances, which thus become pseudomorphs.
Syntheses.— Crystals of halite have been produced by sublimation from the gases of furnaces, and by crystallization from solution contain- ing sodium chloride.
Occurrence and Origin —Salt/occurs most abundantly in the water of the ocean, of certain salt lakes, of brines buned deep within the rocks in some places, and as beds interstratified with sedimentary rocks. In the latter case it is associated with sylvite (KC1), anhydrite (CaSO*), gypsum (CaSO4 2H2O), etc., which, lite the halite, are believed to have been formed by the drying up of salt lakes or of portions of the ocean that were cut off from the main IxxLy of water, since the order of occurrence of the various beds is the sa me as the order of deposition ot the corre- sponding salts when precipitated by the evaporation of sea water at varying temperatures (Ojanp pp. 22, 23.)
Below are given figures* showing the composition of the salts in the water of the ocean, of GF -at Salt Lake, and of the Syracuse, N. Y. and
136 Descriptive Mineralogy
Michigan artificial brines (produced by forcing water to the buned rock salt)
NaCl CaCk MgCl2 NaBr KC1 Na2S04 K2S04 CaS04 MgS04 I 77 07 7 86 i 30 3 89 4 63 5 29
II. 79 57 10 oo 6 25 3 60 58
Iii 95 97 90 69 . 2 54
Iv. 91 95 3 19 2 48 2 39
I Atlantic Ocean
II Great Salt Lake
HI New York bnnes
IV Michigan bnnes
Localities —The principal mines of halite, or rock salt, are at Wie- liczka, Poland, Hall, Tyrol, Stassfuit, Germany, where fine crystals are found, the Valley of Cardova, Spain, in Cheshire, England and in the Punjab region of India At Petit Anse in Louisiana, in the vicinity of Syracuse, N Y , and in the lower peninsula of Michigan thick beds of the salt are buried in the rocks far beneath the surface Much of the salt is comparatively pure and needs only to be crushed to become usable In most cases, however, it is contaminated with clay and other sub- stances In these cases it must be dissolved in water and recrystallized before it is sufficiently pure for commercial uses
The best known deposits are at Stassfurt where there is a great thick- ness of alternating layers of halite, sylvite (KC1), anhydrite, gypsum, kieseiite (MgSQa-IfeO) and various double chlorides and sulphates of potassium and magnesium. Although the halite is in far greater quan- tity than the other salts, nevertheless, the deposit owes most of its value to the latter, especially the potassium salts (comp. pp. 137, 142)
Uses. — Besides its use in curing meat and fish, salt is employed in glazing pottery, in enameling, in metallurgical processes, for clearing oleomargarine, making butter and in the more familiar household oper- ations. It is also the chief source of sodium compounds.
Production —Most of the salt produced in the United States is ob- tained directly from rock salt layers by mining or by a process of solu- tion, in which water is forced down into the buned deposit and then to the surface as bnne, which is later evaporated by solar or by artificial heat In the district of Syracuse, N. Y , salt occurs in thick lenses interbedded with soft shales In eastern Michigan and in Kansas salt is obtained from buried beds of rock salt, and in Louisiana from great dome-like plugs covered by sand, day and gravel. Some of the masses in this State are 1,756 ft. thick.
Chlorides, Fluorides, Etc 137
The salt production of the United States for 1912 amounted to 33,- 324,000 barrels of 280 Ib each, valued at $9,402,772 Of this quantity 7,091,000 barrels were rock salt
The imports of all grades of salt during the same time were about 1,000,000 barrels and the exports about 440,000 barrels.
Sylvite (KC1)
Sylvite is isometric, like halite, but the etched figures that may be produced on the faces of its crystals indicate a gyroidal symmetry (pen- tagonal icositetrahedral class) The habit of the crystals is cubic with O(ni) and oo O oo (100) predominating.
Pure sylvite contains 47 6 per cent Cl and 52 4 per cent K, but the mineral usually contains some NaCl and often some of the alkaline sul- phates.
The physical properties of sylvite are like those of halite, except that its hardness is 2 and the density i 99 Its melting temperatuie is 738° and n for sodium light i 4903
When heated before the blowpipe the mineral imparts a violet tinge to the flame, which can be detected when masked by the yellow flame of sodium by viewing it through blue glass Otherwise sylvite and halite react similarly.
Halite and sylvite are distinguished from other soluble minerals by the reaction with the bead saturated with copper oxide, and from one another by the color imparted to the blowpipe flame.
Synthesis — Sylvite crystals have been made by methods analogous to those employed in syntheses of halite crystals
Occurrence — Sylvite occurs associated with halite, but in distinct beds, at Stassfurt, Germany, and at Kalusz, Galicia. It has also been found, together with the sodium compound, incrusting the lavas of Vesuvius.
Uses. — Sylvite Is an important source of potassium salts, large quan- tities of which are used in the manufacture of fertilizers,
Cerargyrite Group
The cerargyrite group comprises the chloride, bromide and iodide of silver. The first two exist as the minerals cerargyrite and bromargyrite, both of which crystallize in the isometric system. The isometric Agl exists only above 146°; below this temperature the iodide is hexagonal. The exhagonal modification occurs as the mineral iodyrite, which, of course, is not regarded as a member of the cerargyrite group
138 Descriptive Mineralogy
Cerargyrite (AgCl)
Cerargynte, or horn silver, is an important silver ore It is usually associated with other silver compounds, the mixture being mined and smelted without separation of the components It is usually recog- nizable by its waxy, massive character
Silver chloride consists of 24 7 per cent chlorine and 75 3 per cent silver, but cerargynte often contains, in addition to its essential con- stituents, some mercury, bromine and occasionally some iodine Crystals are rare They are isometric (hexoctahedral class), with a cubical habit, their predominant forms being oo O oo (100), oo 0(no), 0(in), 20(221) and 202(211) Twins sometimes occur with 0(in) the twinning face The mineral is sometimes found massive, embedded among other min- erals, but is more frequently in crusts covering other substances
The fracture of cerargynte is conchoidal The mineral is sectile Its hardness is i-i 5 and density about 5 5 Its color is grayish, white or yellow, sometimes colorless. On exposure to light it turns violet- brown It is transparent to translucent and its streak is white It is a very poor conductor of electricity Like halite it is diathermous n for sodium, light 2 071.
In the closed tube cerargynte fuses without decomposition On charcoal it yields a metallic globule of silver, and when heated with oxide of copper m the blowpipe flame it gives the chlorine reaction The min- eral is insoluble in water and in nitric acid but is soluble in ammonia, and potassium cyanide. When a particle of the mineral is placed on a sheet of zinc and moistened with a drop of water, it swells, turns black and is finally reduced to metallic silver, which, when rubbed by a knife blade, exhibits the white luster of the metal.
Cerargyrite is easily distinguished from all other minerals, except the comparatively rare bromide and iodide, by its physical properties and by the metallic globule which it yields on charcoal
Syntheses.— Crystals of cerargynte have been obtained by the rapid evaporation of ammoniacal solutions of silver chloride, and by the cooling of solutions of the chloride in molten silver iodide
Occurrence — The mineral occurs in the upper (oxidized) portions of veins of argentiferous minerals, where it is associated with native silver and oxidized products of various kinds
Localities.— The most important localities of cerargynte are in Peru, Chile, Honduras and Mexico, where it is associated with native silver. It is also found near Leadville, Colo*; near Austin, in the Comstock lode, Nev., and at the Poorman Mine, and in other mines in Idaho
CHLORIDES, FLfORIDES, ETC
and at several places in Utah. Good crystals occur in the Poorman Mine.
Extraction — When a silver ore consists essentially of cerargynte the metal may be extracted by amalgamation Ores containing compara- tively small quantities of cerargynte are smelted
Production — The quantity of cerargyrite mined cannot be safely estimated. As has been stated, it is usually wrought with other silver ores,
The Fluorides
The fluorides are salts of hydrofluoric acid. There are several known to occur as minerals, but only two, the fluoride of calcium and
FIG 60 —Group of Fluonte Crystals from Weardale, Co., Durham, England (Foote
Mineral Company )
the double fluorides of sodium and aluminium are of sufficient impor- tance to merit description here.
Fluorite (CaF2)
Fluorite, or fluorspar, is the principal source of fluorine. It is usually a transparent mineral that is characterized by its fine color and its hand-
Descriptive Mineralogy
some crystals (Fig 60) Perhaps there is no other mineral known that can approach it m the beauty of its crystal groups The uncrystallized fluorite may be massive, granular or fibrous
Fluonte is a compound of Ca and F in the proportion of 48 9 per cent F and 51 i per cent Ca Chlorine is occasionally present in minute quantities, and SiCfe, AkOs and Fe20s are always present A sample of commercially prepared fluonte from Marion, Ky , gave
CaF2
Si02
CaC03
MgO
The crystallization is isometric (hexoctrahedral class), and inter- penetration twins are frequent The principal forms observed are
Fig 6 1
Fig 62
FIG 61 —Crystal of Fluonte with oo O oo , 100 (a) and 02, 210 (e). FIG 62 — Interpeaetration Cubes of Fluonte, Twinned about O(in)
0(ui), oo O oo (100), oo 02(210) and 462(421) (Fig 61), but some crys- tals are highly modified, as many as 58 forms having been identified upon the species The twins, with O(ni) the twinning plane, are usually interpenetration cubes, or cubes modified on the corners by the octa- hedrons (Fig. 62). The mineral occurs also in granular, fibrous and earthy masses.
The cleavage of fluorite is perfect parallel to 0(in). The mineral is brittle, its fracture is uneven or conchoidal, its hardness is 4 and its density about 3.2. It at 1387°. Its color is some shade of yel- low, white, red, green, blue or purple, its luster vitreous, and its streak is white Many specimens are transparent, some are only translucent. Most specimens phosphoresce upon heating A vanety that exhibits a green phosphoresence is known as cfdorophane The index of refraction for sodium light is 1 43385 at 20°. The mineral is a nonconductor of electricity.
The color of the brightly tinted varieties was formerly thought to be due to the presence of minute traces of organic substance since it is lost
Chlorides, Fluorides, Etc 141
or changed when the mineral is heated, but recent observations of the effect of radium emanations upon light-colored specimens indicate a deepening of their color by an increase in the depth of the blue tints. This suggests that the coloring matter is combined with the CaF2- It may be a colloidal substance
In the closed tube fluonte decrepitates and phosphoresces When heated on charcoal it fuses, colors the flame yellowish red and yields an enamel-like residue which reacts alkaline to litmus paper Its powder treated with sulphuric acid yields hydrofluoric acid gas which etches glass. The same effect is produced when the powdered mineral is fused with four times its volume of acid potassium sulphate (HKSO*) in a glass tube The walls of the tube near the mixture become etched as though acted upon by a sand blast.
Fluonte is easily distinguished by its cleavage and hardness from most other minerals It is also characterized by the possession of fluorine for which it gives dear reactions.
Syntheses — Crystals are produced upon the cooling of a molten mix- ture of CaF2 and the chlorides of the alkalies, and by heating amorphous CaF2 with an alkaline carbonate and a little HC1 in a closed tube at 250°.
Occurrence, Localities and Origin. — The mineral occurs in beds, in veins, often as the gangue of metallic ores and as crystals on the wails of cavities in certain rocks. It is the gangue of the lead veins of northern England and elsewhere. Handsome crystallized specimens come from Cumberland and Derbyshire, England; Kongsberg, Norway, Cornwall, Wales, and from the mines of Saxony. In the United States the mineral forms veins on Long Island; in Blue Hill Bay, Maine, at Putney, in Vermont; at Plymouth, Conn ; at Lockport and Macomb, in New York, at Amelia Court House, Va., and abundantly in southeastern Illinois and the neighboring portion of Kentucky, where it occurs asso- ciated with zinc and lead ores. These last-named localities, the neigh- borhood of Mabon Harbor, Nova Scotia, and Thunder Bay, Lake Superior, afford excellent crystal groups. In nature fluonte has been apparently produced both by crystallization from solutions and by pneumatolytic processes
Since fluorite is soluble in alkaline waters, its place in the rocks is often occupied by calcite, quartz or other minerals that pseudomorph it.
Uses — The mineral is used extensively as a flux in smelting iron and other ores, in the manufacture of opalescent glass, and of the enamel coating used on cooking utensils, etc It is also used in the manufacture of hydrofluoric acid, which, in turn, is employed in etching glass The brighter colored varieties are employed as material for vases and the
142 Descriptive Mineralogy
transparent, colorless kinds are ground into lenses for optical instruments The mineral is also cut into cheap gems, l:no\vn according to color, as false topaz, false amethyst, etc Except used for making lenses or as a precious stone, fluorite is prepared for shipment by crushing, wash- ing and screening A portion is ground
Production — The fluonte produced in the United States is obtained mainly from Illinois and Kentucky, though small quantities are mined in Colorado, New Mexico and New Hampshire The production in 1912 amounted to 116,545 tons, valued at $769,163. Of this, 114,410 tons came from Illinois and Kentucky. The imports were 26,176 tons, valued at $71,616
The Double Chlorides And Double Fluorides
These double salts are apparently molecular compounds, in which usually two chlorides or two fluorides combine, as in AlFa+3NaF Moreover, one of the members of the combination of chlorides is nearly always either the sodium or the potassium chloride The law of this combination is expressed by Professor Remsen in these words " The number of molecules of potassium or sodium chloride which combine with another chloride is limited by the number of chlorine atoms con- tamed m the other chloride " Thus, if NaCl makes double salts with MC12, in which M represents any bivalent element, only two are possible, viz- MCl2+NaCl and MCl2+2NaCl With MC13 three double salts with sodium may be formed, etc These double salts are not regarded as true molecular compounds, but they are looked upon as compounds in which Cl and F are bivalent like oxygen
Carnallite (KMgCls 6H20)
Carnallite may be regarded as a hydrated double chloride of the composition MgCk KC1 6H2O with 14 i per cent K, 8 7 per cent Mg, 38 3 per cent Cl and 39 o per cent H20 It occurs m distinct crys- tals but more frequently in massive granular aggregates
Its crystallization is orthorhombic (bipyramidal class), but the habit of its crystals is usually hexagonal because of the nearly equal develop- ment of pyramids and brachydomes. Its axial ratio is .5891 i i 3759. Crystals are commonly bounded by oo P(no), P(in), JP(ri2), £P(ii3), oo P eo (oio), 2? a& (021), P 56 (on), oa (023), oP(ooi), and P 56 (101). The angle no A 3 10=61° 2oJ'.
Carnallite is colorless to milky white, transparent or translucent, and has a fatty luster Many varieties appear red in the hand specimens
Chlorides, Fluorides, Etc 143
because of the inclusion of numerous small plates of hematite or goethite, or yellow because of inclusions of yelkm liquids or tiny crystals. The mineral has a hardness of 1-3, and a density of 1.60 It possesses no cleavage but has a conchoidal fracture It is not an electrical conductor. It is deliquescent and has a bitter taste Its indices of refraction for sodium light are i 467, jS= 1.475, 1-494
Before the blowpipe carnalhte fuses easily. In the closed tube it becomes turbid and gives off much water, which is frequently accom- panied by the odor of chlorine. It melts in its own water of crystalliza- tion. When evaporated to dryness and heated by the blowpipe flame a white mass results which is strongly alkaline. The mineral dissolves in water, forming a solution which reacts for Mg, K and Cl
Carnalhte is easily recognized by its solubility, its bitter taste and the reaction for chlorine
Synthesis — The mineral separates in measurable crystals from a solu- tion of MgCl2 and KC1
Occurrence and Origin — Carnalhte occurs hi beds associated with sylvite, halite, kieserite (p. 246), and other salts that have been pre- cipitated by the evaporation of sea water or the water of salt lakes
Localities — It is found in large quantity at Stassfurt, Germany, at Kalusz, in Galicia and near Maman, in Persia
Uses. — Carnalhte is used as a fertilizer and as a source of potash salts.
Cryolite (NasAlFe)
Cryolite usually occurs as a fine-grained granular white mass in which are often embedded crystals of light brown iron carbonate (sider- ite). The formula given above demands 54 4 per cent F, 12 8 per cent Al and 32.8 per cent Na. Analyses of pure white specimens correspond veiy closely to this
The mineral is monoclinic (prismatic class), but crystals are exceed- ingly rare and when found they have a cubical habit. Their axial ratio is a : b : =.9662 : i . i 3882. £=89° 49'. The principal forms are ooP(no), oP(ooi), Pco(oTo), —P 00(010) and P 06(100), thus re- sembling the combination of the cube and octahedron. Twins are com- mon, with oo P(no) the twinning plane
The deavage of cryolite is perfect parallel to oP(coi). Its fractine is uneven. Hardness is 2 5 and density about 3. Its color is snow-white inclining to red and brown. Its luster is vitreous or greasy and the mineral is translucent to transparent Because of its low index of refraction, massive specimens suggest masses of wet snow. The re-
144 Descriptive Mineralogy
fractive index /3 for sodium light is i 364 It is a nonconductor of electricity.
Cryolite is very easily fusible, small pieces melting even at the low temperature of a candle flame The mineral is soluble in sulphuric acid with the evolution of HF When fused in the closed tube with KHS04 it yields hydrofluoric acid, and -ft hen fused on charcoal fluorine is evolved The residue treated with Co(NOs)2 and heated gives the color reaction forAl
By the aid of its reactions with sulphuric acid, its fusibility and its physical properties cryolite is easily distinguished from fluonte, which it most resembles, and from all other minerals.
Occurrence, Localities and Origin —The occurrences of cryolite are very few It has been found in small quantities near Miask in the Ihnen Mts, Russia, near Pike's Peak, Colo, and in the Yellowstone National Park. Its puncipal occurrence is m a great pegmatitic vein cutting granite near Ivigtut, Greenland, whence all the mineral used in the arts is obtained The associates of the cryolite at this place are sidente, galena, chalcopynte, pnte, fluonte, topaz and a few rare minerals The vein is said to be intrusive into the granite. It is believed to be a magmatic concentration
Uses. — Cryolite was formerly employed principally in the manufac- ture of alum and of salts of sodium. At present it is used as a flux in the electrolytic production of aluminium, and is employed in the man- ufacture of white porcelain-like glass, and in the process of enameling iron The mineral is quarried in Greenland and imported into the United States to the extent of about 2,500 tons annually. Its value is about $25 per ton.
The Oxychlorides
The oxychlorides are combinations of hydroxides and chlorides Some of them are " double salts " in the sense in which this word is explained above. Atacamite is a combination of the oxychlonde
Cu(OH)Cl with the hydroxide Cu(OH)2, or Ncu Cu(OH)2.
Atacamite (Cu(OH)Cl-Cu(OH)2)
Atacamite is especially abundant in South America The mineral is usually found in crystalline, fibrous or granular aggregates of a bright green color
Analyses of specimens from Australia and from Atacama, Chile, yield.
Chloeides, Fluorides, Etc 145
Cu
CuO
H20
Total
12 O2
Is 83
55 7°
Ioo 00
Austraha Atacama, Chile.
The formula lequires 16 6 per cent Cl, 14.9 per cent Cu, 55 8 per cent CuO and 12 7 per cent EkO.
The crystallization of atacamite is orthorhombic (bipyramidal class), with a : b : £=.6613 : i : .7529 Its crystals are usually slender prisms bounded by ooP(no), ooP£(i2o), ooPoo (oio), P66 (011), oP(ooi) and P(III), or tabular forms flattened m the plane of the macropinacoid oo P 56 (100). Twins are common, with the twinning plane ooP(no).
The cleavage of atacamite is perfect parallel to oo P 06 (oio). Its fracture is conchoidal. Its hardness is 3-3 5 and density about 3 76. Pure atacamite is of some shade of green, varying between bright shades and emerald. Its aggregates often contain red or brown streaks or grains due to the admixture of copper oxides. It is transparent to trans- lucent. The streak of the mineral is apple-green It is a nonconductor of electricity Its indices of refraction for green light are a=i 831, 1.861,7=1 880
In the closed tube atacamite gives off much water with an acid reac- tion, and yields a gray sublimate In the oxidizing flame it fuses and tinges the flame azure blue (reaction for copper chloride). It is easily reduced to a globule of copper on charcoal and is easily soluble in acids.
Atacamite is readily distinguished from garmerite, malachite and other green minerals by its solubility in acids without effervescence and by the azure blue color it imparts to the flame.
Synthess. — Crystals have been produced by heating cuprous oxide (CugO) with a solution of FeCls, in a closed tube at 250°.
Occurrence, Localities and Origin — The mineral is most abundant along the west side of the Andes Mountains in Chile and Bolivia. It occurs also in South Australia, in India, at Ambriz, on the west coast of Afnca, in southern Spain, in Cornwall, where it forms stalactite tubes, in southern California, and near Jerome, Arizona. It is formed as the result of the alteration of other copper compounds, and is found most abundantly in the upper portions of copper veins Atacamite changes on exposure to the weather into the carbonate, malachite, and the sili- cate, chrysocolla.
Uses. — The mineral is an important ore of copper, but it is mined with other compounds and consequently no records of the quantity obtained are available.
Chapter Vii The Oxides
THE oxides (except water) and the hydroxides may be regarded as derivatives of water, the hydrogen being replaced wholly or in part by a metal. When only part of the hydrogen is replaced an hydroxide results, when all of the hydrogen is replaced an oxide results Thus, sodium hydroxide, NaHO, may be looked upon as HgO, in which Na has replaced one atom of H, and sodium oxide, Na20, as KfeO in which both hydrogen atoms have been replaced by this element Ferric oxide and ferric hydroxide bear these relations to water:
H-0— H
H— O— H, Fe— O— Fe, feme oxide, H— O— Fe, ferric hydroxide
YFe203 H-0/ Fe(OH)3
The oxides constitute a very important, though not a large, class of minerals Some of them are among the most abundant of all minerals They are separated into the following groups: Monoxides, sesqui- oxides, dioxides and higher oxides.
The Monoxides
Ice (H2O)
The properties of ice are so well known that they need no special description in this place The mineral is never pure, since it contains, in all cases, admixtures of various soluble salts. Its crystallization is hexagonal and probably trigonal and hemimorphic (ditngonal pyram- idal class). Crystals are often prismatic, as when ice forms the cover- ing of water surfaces, or the bodies known as hailstones In the form of snow the crystals are often stellate, or skeleton crystals, and sometimes
Oxides
hollow prisms The principal forms observed on ice crystals are oP(oooi) ooP(ioTo), |P(iol2), P(ioTi) andtfUoli) (Fig 63).
The hardness of ice is about 1.5 and its density 9181 It is trans- parent and colorless except m large masses when it appears bluish. Its fracture is conchoidal It possesses no distinct cleavage Its fusing
FlG. 63 — Photographs of Snow Crystals, .Magnified about 15 Diameters (After
Benttey and Perkins )
point is o° and boiling point 100°. It is a poor conductor of electricity. Its indices of refraction for sodium light at 8° are: 1.3090, 1.3133.
Copper Oxides
There are two oxides of copper, the red cuprous oxide (Cu2O) and the black cupric oxide (CuO). Both are used as ores, the former being much more important a source of the metal than the latter
Cuprite (Cu2O)
Cuprite occurs in crystals, in granular and earthy aggregates and massive The mineral is usually reddish brown or red and thus is easily distinguished from most other minerals. Its composition when pure is 88.8 per cent Cu and n 2 per cent O.
In crystallization the mineral is isometric, in the gyroidal hemihedral division of the system (pentagonal icositetrahedral dass). Its pre-
148 Descriptive Mineralogy
dominant forms axe ooOoo(ioo), 0(iu), ooO(uo), 0002(210), 202(211), 20(221) and 301(321), sometimes lengthened out into capillary crystals, producing fibrous varieties (var chdcotrchte).
The cleavage of cupnte is fairly distinct parallel to O(in) Its frac- ture is uneven or conchoidal Its hardness is 3 5-4 and density about 6 The mineral is in some cases opaque, oftener it is translucent or even transparent in very thin pieces By reflected light its color is red, brown and occasionally black. By transmitted light it is crimson When gently heated transparent varieties turn dark and become opaque, but they reassume their original appearance upon cooling. Its streak is brownish red and has a brilliant luster When rubbed it becomes yellow and finally green. The luster of the mineral vanes between earthy and almost vitreous It is a poor conductor of electricity, but its con- ductivity increases rapidly with using temperature. Its refractive index for yellow light 2.705
In the blowpipe flame cuprite fuses and colors the mantle of the flame green If moistened with hydrochloric acid before heating the flame becomes a brilliant azure blue. On charcoal the mineral first fuses and then is reduced to a globule of metallic copper. It dissolves in strong hydrochloric acid, forming a solution which, when cooled and diluted with cold water, yields a white precipitate of cuprous chloride (Cu2Cl2).
Cupnte may easily be distinguished from other minerals possessing a red streak by the reaction for copper — such as the production of a metal globule on charcoal, and the formation of cuprous chloride in con- centrated hydrochloric acid solutions by the addition of water. More- over, the mineral is softer than hematite and harder than reaglar, cin- nabar and proitsttte.
Cuprite suffers alteration very readily. It may be reduced to native copper, in which case the copper pseudomorpbs the cuprite, or, on ex- posure to the air it may be changed into the carbonate, malachite, pseudomorphs of which after cupnte are common.
Syntheses — Crystals of cupnte have frequently been observed on copper utensils and coins that had been buried for long periods of time. Crystals have also been obtained by long-continued action of NHs upon a mixture of solutions of the sulphates of iron and copper, and by heating a solution of copper sulphate and ammonia with iron wire in a dosed tube
Occurrence Origin and Localities — Cuprite often occurs as well defined crystals embedded in certain sedimentary rocks in the upper, oxidized portions of copper veins, and in masses m the midst of other copper ores, from which it was produced by oxidation processes* It is
Oxides 149
found as crystals in Thuringia, in Tuscany, on the island of Elba, in Cornwall, Eng , at Chessy, France, and near Coquimbo, in Chile. In Chile, m Peru, and in Bolivia it exists in great masses
In the United States it occurs at Cornwall, Lebanon Co , Penn. It is also found associated with the native copper on Keweenaw Point, Mich , at the copper mines in St. Genevieve Co , Mo ; at Bisbee and at other places in Arizona The fibrous vanety known as chalcoinchite is beautifully developed at Morenci in the same State.
Uses —Cuprite is mined with other copper compounds as an ore of copper.
Melaconite, or Tenorite (CuO)
Melaconite, or tenonte, is less common than cuprite. It usually occurs in massive forms or in earthy masses Crystals are rare Its composition is 79 8 per cent Cu and 20 2 per cent 0.
In crystallization melacomte is tnchnic with a monochnic habit. Its axial ratio is a : b : c=i 4902 : i : 1 3604 and £=99° 32'. The angles a and 7 are both 90°, but the optical properties of the crystals proclaim their tnchnic symmetry.
The mineral possesses an easy cleavage parallel to oP(ooi). Its frac- ture is conchoidal and uneven, its hardness 3 to 4 and density about 6. When it occurs in thin scales its color is yellowish brown or iron gray. When massive or pulverulent it is dull black. Its streak is black, chang- ing to green when rubbed. Its refractive index for red light is 2 63. It is a nonconductor of electricity.
The chemical reactions of melaconite are precisely like those of cu- pnte, with the exception that the mineral is infusible.
Melaconite is distinguished from the black minerals that contain no copper by its reaction for this metal It is distinguished from covelhte and other dark-colored sulphides containing copper by its failure to give the sulphur reaction.
Syntheses — Crystals of melaconite have been found in the flues of furnaces in which copper compounds and moist NaCl are being treated. They have also been obtained by the decomposition of CuCk by water vapor
Occurrence, Localities and Origin.— The mineral usually occurs associ- ated with other ores of copper, from which it has been formed, in part at least, by decomposition. It is mined with these as jmt ore. Thin scales are found on the lava of Vesuvius, where it must have been f onned by sublimation. Masses occur at the copper mines of Ducktowu, Temi.
150 Descriptive Mineralogy
Zincite (ZnO)
Zincite is the only oxide of the zinc group of elements known It is rarely found in crystals It usually occurs m massive forms associated with other zinc compounds.
Pure zmcite is a compound containing 80 3 per cent Zn and 19 7 per cent 0, Since, however, the mineral is frequently admixed with man- ganese compounds it often contains also some manganese and a little iron. A specimen from Sterling Hill, N J , gave 98 28 per cent ZnO, 6 50 per cent MnO and 44 per cent Fe20g
Natural crystals of zmcite are very rare From a study of artificial crystals it is known that the mineral is hexagonal and hemimorphic (dihexagonal pyramidal class). The principal forms observed are ooP(ioTo), ooP2(ii2o), oP(oooi), P(ioTi), P2(ii22) and various other Fro. 64 —Zincite Crystal pyramids of the ist and 2d orders Their habit with oop, iolo (m). 1S hemimorphic with P(iori) and oP(oooi) at p, roll (p) and oP, oppOSite ends of a short columnar crystal 0001 W (Fig. 64)
The cleavage of incite is perfect parallel to oP(oooi) Its fracture is conchoidal, its hardness 4-4 5 and density about 5 8 Although color- less varieties are known, the mineral is nearly always deep red or orange- yellow, due most probably to the manganese present in it The streak of the red varieties is orange- yellow. Its indices of refraction are about 2 The mineral is a conductor of electricity.
When heated in the closed tube the common variety of zmcite blackens, but it resumes its original color on cooling With the borax bead it gives the manganese reaction Heated on charcoal it coats the coal with a white film, which, when moistened with cobalt solution and heated again with the oxidizing flame of the blowpipe, turns green The mineral dissolves in acids
When exposed to the atmosphere zmcite undergoes slow decomposi- tion to zinc carbonate
Syntheses — Zinc oxide crystals are frequent products of the roasting of zinc ores in ovens They have also been produced by the action of zinc chloride vapor upon lime and by the action of water upon zinc chloride at a red heat.
Occurrence and Locafofoes — The mineral occurs only in a few places It is found with other zinc and manganese minerals near Ogdensburg,
Oxides 151
and at Franklin Furnace, m Sussex Co , N J , m the form of great layers in marble, that are bent into troughs The lajers are probably veins that were filled from below by emanations from a great underground reservoir of igneous rock
Uses — Most of the zmcite produced in the United States is used in the manufacture of zinc oxide The ore, which consists of a mixture of zincite, franklimte (see p 199), and willemite (see p 306), is crushed and separated into its component parts by mechanical processes The separated zmcite is then mixed with coal and roasted The zinc oxide is volatilized and is caught m tubes composed of bagging. The willemite and franklimte are smelted to metallic zinc and the residues are used m the manufacture of spiegeleisen
Production — Formerly this mineral, together TMth the silicate found associated with it in New Jersey, constituted the most important source of zinc in this country At present most of the metal is obtained from sphalerite Of the 380,000 tons of zinc in spelter and zinc compounds produced in the United States during 1912 about 69,760 tons were made from zmcite and the ores associated with it. This had an esti- mated value of $9,626,991.
The Sesquioxides
The sesquioxides (R20s) include a few compounds of the nonmetals that are comparatively rare and a group of metallic compounds that includes two minerals of great economic importance. One of these, hematite (FeaOa), is the most valuable of the iron ores
Arsenolite— Claudetite Group
The only group of the nonmetallic sesquioxides that need be referred to in this place comprises those of arsenic and antimony. This is an isodimoiphous group including four minerals.
Isometric Monochmc
Arsenohte As20s Claudetite
Senarmoutote Sb20s Valenttmte
All the minerals of the group are comparatively rare. The isometric forms occur in well developed octahedrons and in crusts covering other minerals They are also found in earthy masses. It is probable that at high temperatures the isometric forms pass over into the monodinic modifications, as some of the latter have been abserved to consist of aggregates of tiny octahedrons. Crystals of daudetite are distinctly
152 Descriptive Mineralogy
monoclinic, but they are so thinned as to possess an orthorhombic habit Valentmite crystals, on the contrary, appear to be plainly orthorhombic, but their apparent orthorhombic symmetry may be due to submicroscopic twinning of the same character as that in claudetite, but which in the latter mineral is macroscopic
All four minerals occur as weathered products of compounds contain- ing As or Sb They give the usual blowpipe reactions for As or Sb In the closed tube they melt and sublime
Arsenolite (As2Os) is colorless or white Its specific gravity is 3,7 and refractive index for sodium light i 755 It usually occurs in octa- hedrons, or m combinations of 0(in) and ooO(no), but these when viewed in polarized light are often seen to be amsotropic The mineral is found also in aggregates of hair-like crystals with a hardness of i 2 It is soluble in hot water, yielding a solution with a sweetish taste
Senarmonite (SbgOs) is gray or white Its density is 5 2 and n=2 087 for yellow light Its octahedral crystals are also often aniso- tropic, its hardness=2 It is soluble in hot HC1 but is only very slightly soluble in water When heated it turns yellow, but becomes white again upon cooling
Claudetite (As2Os) is monochmc prismatic, with a : b : 4040 : i
: 3445 and /3=86° 03' Its white crystals are usually tabular parallel
to oo P ao (oio) and are twinned, with oo P 56 (100) the twinning plane
Their cleavage is parallel to oo P (oio) and their density is 4 15
2.5 The mineral is an electrical nonconductor
Valentinite (Sb2Os) is apparently orthorhombic bipyramidal (pos- sibly monoclimc prismatic) with a : b : 3914 i 3367 Its crystals are tabular or columnar in habit and are very complex The mineral is found also in radial groups of acicular crystals and m granular and dense masses Its color is white, pink, gray or brown, and streak white Its density is 5 77 and hardness 2 5-3. It is insoluble in HC1 It is a nonconductor of electricity
CORUNDUM GROUP t
The sesquioxides of aluminium and iron constitute an isomorphous group crystallizing in the rhombohedral division of the hexagonal sys- tem (ditngonal scalenohedral class) Both the aluminium and iron compounds, corundum and hematite are of great economic importance
Oxides
Hematite (Fe20a)
Hematite is one of the most important minerals, if not the most important one, from the economic standpoint, smce it is the most val- uable of all the iron ores It is known by its dark color and its red powder It occurs in black, glistening crystals, in yellow, brown or red earthy masses, in granular and micaceous aggregates and in botryoidal and stalactitic forms
Chemically, the mineral is Fe20a corresponding to 30 per cent 0 and 70 per cent Fe. In addition to these constituents, hematite often con- tains some magnesium and some titanium. By increase in the latter element it passes into a mineral which has not been distinguished from ilmenite (see p 462)
The habit of hematite crystals is nearly always rhombohedraL
FIG* 65— Hematite Crystals with R, loTi (r), |P2, 2243 JR 1014 oop2l 1 1 20 (0) and oR, oooi (c)
Their axial ratio is a : c=i : 1.3658, and the predominant forms are R(ioTi), iR(iol4), 2(2243), the prisms oo P(ioTo) and ooP2(ii2o) and often the basal plane (Fig. 65) In addition, about no other forms have been identified The crystals are often tabular, and sometimes are grouped into aggregates resembling rosettes. In many cases the terminal faces are rounded A parting is often observed parallel to the basal plane, due to the occunence of the mineral in aggregates in which each crystal is tabular.
Hematite has no well defined cleavage Its fracture is conchoidd or earthy. Its crystals are black, glistening and opaque, except in very small splinters These are red and transparent or translucent. Earthy varieties are red. The streak of all varieties is brownish red or cherry- red. The hardness of the crystallised hematite is 5.5-6.5 aad its density about 5.2. It is a good conductor of electricity. Its refractive indices are: 60=3.22, 6=2.94 for yellow light.
The mineral is infusible before the blowpipe. In the reducing flame on charcoal it becomes magnetic, and when heated with soda it is reduced to a magnetic metallic powder It is soluble IB strong hydrochloric acid.
154 Descriptive Mineralogy
The crystalline and earthy aggregates of hematite to which distinct names have been given are
Specular, when the aggregate consists of grains with a glistening, metallic luster, like the luster of the crystals When the grains are thin tabular the aggregate is said to be micaceous
Columnar or fibrous, when in fibrous masses The color is usually brownish red and the luster dull The botryoidal, stalactic and various imitative forms belong here Red hematite is a compact red variety in which the fibrous structure is not very pronounced
Red ocher is a red earthy hematite mixed with more or less clay and other impurities
Clay ironstone is a hard brownish or reddish variety with a dull luster It is usually a mixture of hematite with sand or clay
Oolitic ore is a red variety composed of compacted spherical or nearly spherical grams that have a concentric structure
Fossil ore differs from oolitic ere mainly in the fact that there are present in it small shells and fragments of shells that are now composed entirely of hematite
Martite is a pseudomorph of hematite after magnetite.
Hematite is distinguished from all other minerals by its red powder and its magnetism after roasting
Syntheses — Crystals of hematite are obtained by the action of steam on ferric chloride at red heat, by heating ferric hydroxide with water containing a trace of NH*F to 250° in a closed tube, and by cooling a solution of Fe20s in molten borax or halite
Occurrence and Origin — Hematite is found in beds with rocks of nearly all ages It occurs also as a deposit on the bottoms of marshy ponds, and m small grams m the rocks around volcanic vents The crystallized variety is often deposited on the sides of clefts in rocks near volcanoes and on the sides of certain veins It is produced by sublima- tion, by sedimentation and by metasomatic processes
Localities —Handsome crystals occur on the island of Elba, near Limoges in France, m and on the lavas of Vesuvius and Etna, at many places in Switzerland, Sweden, etc , and at many in the United States
Beds of great economic importance occur m the Gogebic, Menommee and Marquette districts in Michigan; m the Mesabe and Vermilion districts in Minnesota, m the Pilot Knob and Iron Mountain districts in Missouri, and in the southern Appalachians, especially m Alabama
Uses. — In addition to its use as an ore the fibrous variety of hematite is sometimes cut into balls and cubes to be worn as jewelry. The earthy varieties are ground and employed in the manufacture of a dark red
Oxides 155
paint such as is used on freight cars, and the ponder of some of the mass- ive forms is used as a polishing ponder
Prodtiction.—Most of the iron ore produced in the United States is hematite, and by far the greater proportion of it comes from the Lake Superior region The statistics for 191 2 follow
QUANTITY (IN LONG TONS) OF IRON ORE MINED IN THE SEVERAL LEAD- ING STATES DURING 1912
Hematite Other Iron Ores Total
Minnesota 34j43i,o°o . . 34,431,000
Michigan 11,191,000 11,191,000
Alabama . . . 3,814,000 749,ooo 4,563,000
New York . 106,327 1,110,000 1,216,327
Wisconsin 860,000 860,000
Tennessee. 246,000 171,000 417,000
Total in U S . 51,345,782 3,804,365 55,150,147
The total production in 1912 was valued at about $104,000,000 Corundum
Corundum is the hardest mineral known, with the exception of dia- mond In consequence of its great hardness an impure variety is used as an abrading agent under the name of emery. It is also one of the most valuable of the gem minerals It occurs as crystals and in granular masses
The mineral is nearly always a practically pure oxide of aluminium of the composition AkOs, in which there are 52 9 per cent Al and 47 i per cent O The impure varieties usually contain some iron, mainly as an admixture in the form of magnetite
The axial ratio of corundum crystals is i : i 36 The forms are usually simple pyramids, among which |P2(2243) and |P2(44S3) are the most common (Fig. 66), and the prism oo P2(ii2o) The basal plane is also common (Fig 67). Many crystals consist of a series of steep prisms and the basal plane, with a habit that may be described as barrel-shaped (Fig 68) The crystals are often rough with rounded edges The prismatic and pyramidal faces are usually striated hori- zontally, and the basal plane by lines radiating from the center
All corundum crystals are characterized by a parting parallel to the basal plane, and often by a cleavage parallel to the rhoinbohedron, due to the presence of lamellae twinned parallel to R(ioli). The fracture o£ the mineral is conchoidal or uneven. Its density is about 4 and its
Descriptive Mineralogy
hardness 9 The mineral possesses a vitreous to adamantine luster It is transparent or translucent Its streak is uncolored Its color varies from white, through gray to vanous shades of red, yellow, or blue The blue varieties are pleochroic in blue and greenish blue shades The mineral is a nonconductor of electricity. Its refractive indices for yellow light are w=i 7690, €=i 7598.
Three varieties of corundum are recognized in the arts: Sapphire, corundum and emery
Sapphire is the generic name for the finely colored, transparent or translucent varieties that are used as gems, watch jewels, meter bearings, etc. The sapphires are divided by the jewelers into sapphires, possessing
Fig 66
Fig 67
Fig 68
FIG 66 — Corundum Crystal with |P2, 4483 (u)
Fee. 67— Corundum Crystal with R, loYi (r), °oPs, 1120 (a), and oR, oooi (c) FIG. 68 — Corundum Crystal Form a, v and c as in previous figures Also £P2, 2243 (n) and — 2R, 0221 ($)
a blue color, rubies, possessing a red shade, Oriental topazes, Oriental emeralds and Oriental amethysts having respectively yellow, green and purple tints.
Corundum is the name given to dull colored varieties that are ground and used as polishing and cutting materials
Emery is an impure granular corundum, or a mixture of corundum with magnetite (FeaO) and other dark colored minerals Emery, like corundum, is used as an abrasive. It is less valuable than corundum powder because it contains a large proportion of comparatively soft material
Powdered corundum when heated for a long time with a few drops of cobalt nitrate solution assumes a blue color The mineral gives no definite reaction with the beads It is infusible and insoluble. It is
Oxides 157
most easily recognized by its hardness The mineral alters to spinel (p 196) and to fibrous and platy aluminous silicates
Syntheses —Corundum crystals have been produced artificially in many different ways, but only recently has the manufacture of the gem variety been accomplished on a commercial scale Amorphous Al2Cs dissolves in melted sodium sulphide and crystallizes from the glowing mass at a red heat By melting Al20s in a mass of some fluoride and. potassium carbonate containing a little chromium, and using~compara- tively large quantities of material, violet and blue rubies were obtained by Fremy and Verneuil Rubies are also produced by melting AfaOs and a little COs for several minutes at a temperature of 2250° C in an electric oven
In recent years reconstructed rubies have become a recognized article of commerce These are crystalline drops of ruby material made by melting tiny splinters and crystals of the mineral in an electric arc
Alundum is an artificial corundum made by subjecting the aluminium hydroxide, bauxite, to an intense heat (5ooo°-6ooo°) m an electric furnace.
Occurrence and Origin — Corundum usually occupies veins in crys- talline rocks or is embedded in basic intrusive rocks and in granular limestone The sapphire varieties are also often found as partially rounded crystals in the sands of brook beds The varieties found in igneous rocks are primary crystallizations from the magmas producing the rocks. The varieties in limestones are the result of metamorphic processes
Localities — Sapphires are obtained mainly from the limestone of Upper Burma They are known also to occur in Afghanistan, in Kash- mir and in Ceylon They are occasionally found in the diamond-bearing gravels of New South Wales and in the bed of the Missouri River, near Helena, Montana In the United States sapphire is mined near the Judith River in Fergus Co , and in Rock Creek in Granite Co., Mont., where it occurs in a dike of the dark igneous rock known as monduquite, and is washed from the placers of three streams in the same State. The only southern mines that have produced gem material are at Franklin and Culsagee, N. C , and from these not any great quantity of stones of gem quality have been taken
The largest sapphire crystal ever found was taken, however, from one of them It weighs 312 Ib , is blue, but opaque. From one of these mines, also, came the finest specimen cf green sapphire (Oriental emerald) ever found
Corundum in commercial quantities occurs on the coast of Malabar,
158 Descriptive Mineralogy
m Siam, near Canton, China, and in southeastern Ontario, Canada. Emery is obtained from several of the Grecian Islands, more particularly Naxos, and from Asia Minor It is mined in the United States at Chester, Mass, and at Peekskill, N Y Crystallized corundum occurs near Litdxfield, Conn , at Greenwood, Maine, at Warwick and Amity, N Y , at Mineral Hill, Penn , m Patrick Co , Va , at Corundum Hill and at Laurel Creek, Macon Co., N C , and at anous points in Georgia, at all of which places it has been mined In all the localities within the United States the corundum occurs on the peripheries of masses of pendotite (ohvine rocks)
Uses — Corundum, emery and alundum, after crushing and washing, are used as abrasives and m the manufacture of cutting wheels.
Production. — The amount of sapphire produced in the United States m 1912 was valued at $195,505 Most of it was used for mechanical purposes, but 384,000 carats were used as gem material
Most of the corundum used in the United States is imported from Canada, where it occurs in Hakburton, Renfrew and neighboring coun- ties in Ontario, as crystals scattered through the coarse-grained crys- talline rocks known as syenite, nephelme syenite and anorthosite
Most of the emery is also imported Only 992 tons with a value of $6,652 were mined in 1912 The imports of corundum and emery were valued at $501,725, but the importation of these substances is gradually diminishing because of the rapid increase in the amounts of alundum and carborundum manufactured In 1912 the production of alundum reached 13,300,000 Ib valued at $796,000,
The Dioxides
The Konmetallic Dioxides
There are but few dioxides of the nonmetals that occur as minerals, and only one of these, quartz, is abundant
Silica Group
Silica (SiOa) occurs in nature in four or five important modifica- tions as follows.
a , tngonal-trapezohedral class, below 575°.
j8 Quartz, hexagonal-trapezohedral class, above 575° and below 870°
Tridymite, rhombic bipyramidal, pseudohexagonal habit. Hex- agonal above 117°.
Cristobdite, tetragonal system, pseudocubic habit Isometric above 140°.
Oxides
Chalcedony is regarded by many mineralogists as a form of quartz, but its index of refraction for red light is n=i 537, which is noticeably lower than that of either ray in quartz, which is 5390, e=i 5480 for the same color Its hardness also is a little less than that of quartz. Some mineralogists believe that all of these properties may be explained on the assumption that the mineral is a mass of fine quartz fibers, perhaps mixed with other substances, but those \vho have investigated it by high temperature methods are inclined to regard it as a distinct mineral
Quartz (Si02)
Quartz vies with calcite for the commanding position among the minerals It is very abundant, and appears under a great variety of
Fig 69
Fig 70.
FEG 69 — Quartz Crystal Exhibiting Rhombohedral Symmetry R, loir (r), — R,
oili (s) and °° R, loTb (m)
FIG 70 — Ideal (A) and Distorted (B) Quartz Crystals Bounded by same Forms as
m Fig 69
forms Often it occurs in distinct crystals At other times it appears as grains without distinct crystal forms, and again it constitutes great massive deposits
Pure quartz consists of 46 7 per cent Si and 53.3 per cent (X Mass- ive varieties often contain, in addition, some opal (Si(OH)4), and traces of iron, calcite (CaCOs), clay, and other impurities
The crystallization of quartz is in the trapezohedral tetartohedral division of the hexagonal system (trigonaUrapezohedral class), at tem- peratures below 575°. When formed above this temperature its sym- metry is hexagonal trapezohedral (hemihedral). The former is known as a. quartz, and the latter as jS quartz. They readily pass one into the other at the stated temperature. The axial ratio is i : i.i. The prin-
cipal forms observed are +R(ioii), -R(om), oo R(ioio), — (1121),
Descriptive Mineralogy
(Fig 74) and a series of steep rhombohedrons and trapezo- hedrons Although these may all be tetartohedral since t he geometrical
FIG 71 — Etch Figures on Two Quartz Crystals of the Same Form, Illustrating Dif- ferences in Symmetry Right-Hand Crystal B Left-Hand Crystal (After Penfidd )
FIG 72 — Group of Quartz Crystals with Distorted Rhombohedral Faces (Foote
Mineral Company )
forms of the first four are not distinguishable from the corresponding hemihedral ones, the crystals possess a rhombohedral symmetry (Fig. 69). The angle ioTiA"iioi 850 46'
Oxides
Often the +R and the -R faces are equslly de\ eloped so that they appear to belong to the hexagonal pyramid P (Fig yoA) Their true character, ho\\ever, is clearly brought out by etching, when figures are produced on the +R and the -R that are differently situated with respect to the edges of the faces (Fig 71) On the other hand, on many crystals some of the R faces are very much enlarged at the expense of the others (Fig 72)
The crystals are commonly pnsmatic Often they are so dis-
Fig 73 Fig 74
FIG 73 — Tapenng Quartz Crystal with Rhombohedral Symmetry Combination
of r, z, m and Two Steep Rhombohedrons B Cross-section near Top. FIG 74 — Quartz Crystals Containing ooR, iolo (m), R, loll (r), — R, oiTi (s),
), — r, 510*1
and — /, sin
onB
), — -/, sT6"i on A, and — r, 1121
torted that it is difficult to detect the position of the c axis (Fig 708) The stnations on oo R(ioTb) are, however, always parallel to the edges between R and ooR When these are sharply marked the position of the vertical axis is easily recognized Many crystals taper sharply toward the ends of the c axis This tapering is due to oscillatory combination of the prism ooR with rhombohedrons
(Fig- 73)-
The habits of the crystals vary with the crystallization of the quartz. On crystals of the 0 phase the +R and — R faces are equally developed and trigonal trapezohedrons are absent. The crystals are hexagonal in
Descriptive Mineralogy
habit Crystals of the a phase usually exhibit marked differences in the size and character of the rhombohedral planes, and trigonal trape- zohedrons may be present on them Such crystals are usually trigonal in habit and prismatic
The small —(1121) faces on all types of crystals (Fig 74) are
always striated parallel to the edge between this plane and +R. By their aid the +R can always be distinguished from the — R This is a matter of some practical importance since plates cut from quartz crystals possess the power of rotating a ray of polarized light. The plates cut
C D
FIG 75 —Supplementary Twins of Quartz
C is a combination of A and B in Fig 74 twinned about P2(ii2o) This is known as the Brazil law
D is a combination of two crystals like B twinned about c as the twinning axis One is revolved 60° with reference to the others, thus causing the r and s faces to fall together Swiss law E is a twin like D, showing portions of planes belonging to each individual It contains also the form s.
from some crystals turn the ray to the right; those cut from others turn it to the left Crystals that produce plates of the first kind are known as right-handed crystals, those that produce plates of the second kind as left-handed crystals. Since this property of quartz plates is employed in the construction of optical instruments for use m the detection of sugars and certain other substances in solution it is important to be able to distinguish those crystals that will yield right-handed plates from those that will yield left-handed ones Observation has shown that
when the - (1121) faces are in the upper right-hand corner of the oo R
plane immediately beneath +R the crystal is right-handed When these faces are in the upper left-hand corner of this oo R plane the crystal
Oxides 163
is left-handed In either case, when (5i5i) is present it occurs
2p2 between -- (1121) and the oo R face beneath +R
Interpenetration of quartz are so common that few crystals can be observed that do not exhibit some evidence of thinning (Fig 75). The twinning plane is oo R, so that the c axes in the twinned individuals are parallel and, indeed, often coincident The R faces and the oo R faces practically coincide in the twinned parts so that the crystals resemble untwinned ones The twinning is exhibited by dull areas of — R on bright areas of +R faces and by breaks in the continuity of the striations on oo R
Other twinning laws have also been observed in quartz, but their discussion as well as the more complete discussion of the mineral's crystallization must be left for larger treatises In the most common of these other laws the individuals are thinned about P2(ii22). See Fig 76
The fracture of quartz is conchoidal Its hard- ness is 7 and density 2 65 Its luster is \itreous, or sometimes greasy Pure specimens are transparent or colorless, but most varieties are colored by the addition of pigments or impurities When the coloring matter is opaque it may be present in sufficient quantity to render the mineral also opaque
on. ± i IT- j r FlG 76— Quart!
The streak is colorless in pure varieties, and of some xwmned about pale shade in colored varieties. The mineral is pyro- p2(n22) electric and circularly polarizing as described above It is an electric insulator at ordinary temperatures Its refractive indices for yellow light are: i 5443, i 5534
Quartz resists most of the chemical agents except the alkalies. It dissolves in fused sodium carbonate and in solutions of the caustic alkalies It is also soluble in HF and to a very slight degree in water, especially in water containing small quantities of certain salts When heated to 575° the a variety passes into the /3 variety, at 870° both varieties pass into tndymite, and at 1470° the tndymite passes over into cristobahte. Gradual fusion occurs just below 1470°.
The varieties of quartz have received many different names depend- ing largely upon their color and the uses to which they are put. They may be grouped for convenience into crystallized and crystalline vari- eties
The principal crystallized varieties are:
164 Descriptive Mineralogy
Rock crystal, the colorless, transparent variety, that often forms distinct crystals This is the variety that is used in optical instruments It includes the Lake George diamonds, rhmestones and Brazilian peb- bles
Amethyst, the violet-colored transparent variety.
Rose quartz, the rose-colored transparent variety.
Citrine or false topa~, a yellow and pellucid kind
Smoky quartz or Cairngorm stone, a smoky yellow or smoky brown variety that is often transparent or translucent, but sometimes almost opaque.
The last four varieties are used as gems, the Cairngorm stone being a popular stone for mourning jewelry
Mlky quartz is the white, translucent or opaque variety such as so commonly forms the gangue m mineral veins and the material of " quartz
Sag&mte is rock crystal including acicular crystals of rutile
Aventurine is rock crystal spangled with scales of some micaceous mineral
The puncipal crystalline varieties are
Chalcedony , a very finely fibrous, transparent or translucent waxy- looking quartz that forms mamillary or botryoidal masses Its color is white, gray, blue or some other delicate shade The water that is always present in it is believed to be held between the minute fibers, and not to be combined with the silica (see also p 159)
Carnehan is the name given to a clear red or brown chalcedony
Chrysoprase is an apple-green chalcedony
Prase is a dull leek-green variety that is translucent
Plasma differs from prase in having a brighter green color and in being translucent
Heliotrope, or lloodstone, is a plasma dotted with red spots of jasper.
All of the colored chalcedonies are used as gems or as ornamental stones
Agate is a chalcedony, or a mixture of quartz and chalcedony , vane- gated in color The commonest agates have the colors arranged in bands, but there are others, like " fortification agate " in which the colors are irregularly distributed, and still others in which the variation in color is due to visible inclusions, as in " moss-agates " The different bands in banded agates often differ in porosity. This property is taken advantage of to intensify the contrast in their colors The agate is soaked in oil, or in some other substance, and is then treated with chem- icals that act upon the material absorbed by it Those bands which
Oxides 165
have absorbed the greater quantity of this material become darker in color than those that have absorbed less
On) % is a very evenly banded agate in which there is a marked con- trast in colors Cameos are onyxes in one band of which figures are cut, leaving another band to form a background
Sardonyx is an onyx in which some of the bands consist of carnelian. It is usually red and white.
Flint, jasper, hornstone and touchstone are very fine grained crystalline aggregates of gray, red or nearly black mixture of opal, chalcedony and quartz They are more properly rocks than minerals Chert is an im- pure flint
Sandstone is a rock composed of sand grains, most of tthich are quartz, cemented by clay, calcite or some other substance. When the cement is quartz the rock is a quartzite Oilstones, honestones and some whetstones are cryptocrystalhne aggregates of quartz, very dense and homogeneous, except for tiny rhombohedral cavities that are thought to have resulted from the solution of crystals of calcite They are gener- ally believed to be beds of metamorphosed chert
Syntheses — Crystallized quartz has been made in a number of ways, both from superheated aqueous solutions and from molten magmas Crystals have been produced by the action of water containing am- monium fluoride upon powdered glass and upon amorphous Si02, and by heating water in a dosed glass tube to high temperatures The separation of crystals from molten magmas is facilitated by the addition of small quantities of a fluoride or of tungsten compounds.
Occurrence and Origin — Quartz occurs as an essential constituent of many crystalline rocks such as granite, gneiss, etc., and as the almost sole component of certain sandstones It constitutes the greater portion of most sands and the material of many veins. It also occurs as pseudo- morphs after shells and other organic bodies embedded in rocks, having replaced the original substance of which these bodies were composed. It is also one of the decomposition products of many silicates. It may thus be primary or secondary in origin. It may result from igneous or aqueous processes, or it may be a sublimation product.
Localities — Quartz is so widely spread in its distribution that only a very few of its most interesting localities can be referred to in this place.
The finest specimens of rock crystals come from Dauphine, France; Carrara, in Tuscany, the Piedmont district, in Italy, and in the United States from Middleville, and Little Falls, N. Y.; the Hot Springs, Arkv and from several places in Alexander Co., N. C. Smoky quartz is found in good crystals in Scotland, at Pans, Me.; in Alexander
166 Descriptive Mineralogy
Co , N C , and in the Pike's Peak region of Colorado The handsomest amethysts come from Ceylon, Persia, Brazil, Nova Scotia and the country around Lake Superior Rose quartz occurs in large quantity at Hebron, Pans, Albany and Georgetown, Me
Fine agates and carnehans are brought from Arabia, India and Brazil. They are abundant in the gravels of Agate Bay and of other bays and coves on the north shore of Lake Superior
Chalcedony is abundant in the rocks of Iceland and the Faroe Islands, in those on the northwest side of Lake Supenor, and in the gravels of the Columbia, the Mississippi and other western rivers
The other valuable varieties of the mineral occur largely in the Far East
Agatized, or sihcified, wood of great beauty exists in enormous quan- tity in an old petrified forest near Cornzo, Ariz It is also found in the Yellowstone Park, near Florissant, Colo , and in other places in the Far West. This wood has had all of its organic matter replaced mole- cule for molecule by quartz in such a manner that its original structure has been perfectly preserved
Uses — Rock crystal is used more or less extensively m the construc- tion of optical instruments and in the manufacture of cheap jewelry Smoky quartz, amethyst, onyx, carnehan and heliotrope stones are used as gems, and agate, prase, chrysoprase and rose quartz as orna- mental stones
Milky quartz, ground to coarse powder, is employed in the manu- facture of sandpaper. Its most extensive use, however, is in the man- ufacture of glass and pottery Earthenware, porcelain and some other varieties of potter's ware are vitrified mixtures of clay and ground quartz, technically known as "flint " Ordinary glass is a silicate of calcium or lead and the alkalies, sodium or potash It is made by melting together soda, potash, lime or lead oxide and ground quartz or quartz sand, and coloring with some metallic salt A pure quartz glass is now being made for chemical uses by melting pure quartz sand
Quartz is sometimes used as a flux in smelting operations In the form of sandstone, it is used as a building stone, and in the form of sand it is employed in various building operations cut from dense quartzites (very hard and compact sandstones) are often employed for lining furnaces
The uses of honestones, oilstones, and whetstones are indicated by their names.
Production — Many varieties of quartz are produced in the United Slates to serve various uses* Vein quartz is crushed and employed
Oxides 167
in the manufacture of wood filler, paints, pottery, scouring soaps, sand- paper and abrasives It is also used in making ferro-silicon, chemical ware, pottery, sand-lime brick, quartz glass, etc The total quantity produced for these purposes in 1912 was 97,874 tons, valued at $191,685
The largest quantity of quartz produced is in the form of sand, of which 38,600,000 tons were marketed in 1912 at a valuation of $15,300,- ooo Sandstone, valued at $6,900,000, was quamed for building and paving purposes Oilstones, grindstones, millstones, etc., which are made from special varieties of sandstone, were produced to the value of $1,220,000
Gem quartz obtained in 1912 was valued at about $22,000. This comprised petrified wood, chrysoprase, agate, amethyst, rock crystal, smoky quartz, rose quartz, and gold quartz (white quartz containing particles of gold).
The Metallic Dioxides
The metallic dioxides include the oxides of tin, titanium, manganese and lead Of these the manganese dioxide may be dimorphous, and the titanium dioxide is-tnmorphous. A dioxide of zirconium is also* known, baddeleytfe, but it is extremely rare. The mineral zircon (ZrSiO4) is often regarded as being isomorphous with cassttente (Sn02) and rutile (Ti02) because of the similarity in the crystallization of the three min- erals The three, therefore, are placed in the same group, in which case all must be regarded as salts of metallic acids, thus: Ti02=TiTiO4, SnO2=SnSn04, zircon =ZrSi04 Other authorities regard zircon as an isomorphous mixture of Ti02 and Si02. In this book zircon is placed with the silicates and the other minerals are considered as oxides.
The two manganese dioxides are poliantfe and pyrolusite. The former is tetragonal and the latter orthorhombic It is possible, however, that the crystals of pyrolusite are pseudomorphs and that the substance is a mixture of poliamte and some hydroxide, as it nearly always contains about 2 per cent HgO.
The three titanium oxides are ridde, which is tetragonal; brookitc, which is orthorhombic, and anatase or octakednte, which is tetragonal. Although rutile and anatase crystallize in the same system, their axial ratios are different, as are also their crystal habits and their physical properties. A few of these differences are indicated below:
Rude a:c=i: .6439; Sp. Gr. =4-283; 2.6158; 2.9029. Anatase -1:1.7771; Sp. Gr. =3.9 ; =2.5618; =2.4886.
168 Descriptive Mineralogy
Of the tliree modifications of titanium dioxide, anatase may be made at a comparatively low temperature Brookite requires a higher temperature for its production, but rutilfc is producible at both high and low temperatures Under the conditions of nature both brookite and anatase pass readily into rutile
Of the seven dioxides discussed, four are members of a single group
Rutile Group
The rutile group consists of four minerals apparently completely isomorphous, though no mixed crystals of any two have been discovered : All crystallize in the tetragonal system (ditetragonal bipyramidal class), with the same forms and with closely corresponding axial ratios The names of the members of the group and their axial ratios follow
Cassitente (Sn02) a c . 6726
Ruttle (Ti02) 6439
Pohamte (Mn02) ' 6647
Plattnente (PbOa) ' 6764
Cassiterite (Sn02)
Cassiterite, or tinstone, is the only worked ore of tin It occurs as rolled pebbles of a dark brown color in the beds of streams, as fibrous aggregates, and as ghstemng black crystals associated with other min- erals in veins
The analyses of cassitente indicate it to be essentially an oxide of tin, or, possibly, a stanyl stannale ((SnOJSnOa), with the composition, Sn=78.6 per cent; 0=2i 4 per cent. The mineral nearly always con- tains some iron oxide and often oxides of tantalum, of zinc or of arsenic The presence of iron and tantalum is so general that most crystals of cassitente may be regarded as isomorphous mixtures of (SnO)(SnOs); Fe(SnOs) and Fe(TaOs)2- Thus, a crystal from the Etta Mine in the Black Hills, S. D, gave Sn02=9436; FeO-i62, Ta205=242 and 8102=100, indicating a mixture of 5 pts of Fe(TaOs)2, 18 pts. of Fe(SnOs) and 303 5 pts of (SnO)(SnOs).
The crystals of cassitente have an axial ratio of i : ,6726. They are usually short prisms in habit They often consist of the simple com- bination P(in) and POO(IOI) (Fig 77), or of these forms, together with sPf (321) and various prisms (Fig 78). Twins are common, the
1An isomorphous mixture of the rutile and cassitente molecules has recently been described from Greifenstem, Austria, but its existence has not yet been con- firmed
Oxides
twinning plane being P oo (101) When the individuals twinned have small prismatic faces the resulting combination is often called a visor twin (Fig 79), because of its supposed resemblance to the vitor of a helmet By repetition of the twinning very complex groupings are produced The angle in A — 58° 19'
Fig 77 Fig 78
FIG. 77. — Cassitente Crystal with P, m (s) and P , 101 fc) FIG 78.— Cassitente Crystal with s, e and °o P, no (m), P2, 210 (A), 3pJ, 321
The cleavage of cassitente is imperfect parallel to oo P oo (100) and P(III) Its fracture is uneven The color of the massive mineral is some dark shade of brown by reflected light, and of the crystals black By transmitted light, the mineral is brown or black Its luster is very brilliant, and its streak is white, gray or brown. The purest specimens
FIG 79 —Cassitente Twinned about P (101), o=ooPoo,ioo A=*VisorTwin.
are nearly transparent, though the ordinary varieties are opaque Their hardness is about 6 5 and density about 7 The mineral is a noncon- ductor of electricity Its refractive indices for yellow light are: w 1 9965, 6=2.0931.
Three varieties of cassitente are recognized, distinguished by physical characteristics The ordinary variety known as tinskme is crystallised
170 Descriptive Mineralogy
or massive. Wood tin is a botryoidal or remform variety, concentric in structure and composed of radiating fibers The third variety is stream tin This consists of water-worn pebbles found m the beds of streams that flow over cassitente-bearmg rocks
Cassitente is only slightly acted upon by acids It may be reduced to a metallic globule of tin only with difficulty, even when mixed with sodium carbonate and heated intensely on charcoal. With borax it yields slight reactions for iron, manganese or other impurities When placed in dilute hydrochloric acid with pieces of granulated zinc, fragments of cassiterite become covered with a dull gray coating of metallic tin which can be burnished by rubbing with a doth or the hand When rubbed by the hand the odor of tin in contact with flesh is easily detected.
The mineral is most easily distinguished from other compounds that resemble it in appearance by its high density and its inertness when treated with reagents or before the blowpipe
Syntheses —Crystals of cassiterite have been obtained by passing steam and vapor of tin chloride or tin fluoride through red-hot porcelain tubes, and by the action of tin chloride \apor upon lime
Occurrence and Origin. — Tinstone is found as a primary mineral in coarse granite veins with topaz, tourmaline, fluorite, apatite and a great number of other minerals It also occurs impregnating rocks, sometimes replacing the minerals of which they originally consisted. In these cases it is the product of pneumatolytic processes. In many places it constitutes a large proportion of the gravel in the beds of streams
Localities and Production — The crystallized mineral occurs at many places in Bohemia and in Saxony, at Limoges in France and sparingly in a few places in the United States, especially near El Paso, Texas, in Cherokee Co., N. C , in Lincoln Co , S C , and near Hill City, S D Massive tinstone and stream tin occur in laige enough quantities to be mined in Cornwall, England, on the Malay Peninsula and on the islands lying off its extremity; in Tasmania; in New South Wales, Victoria and Queensland, Australia; in the gold regions of Bolivia, at Durango in Mexico, and at various points in Alaska, at some of which there, are 400 Ib. of cassiterite in a cubic yard of gravel.
The principal tin ore-producing regions of the world are the Straits, district, including the Malay Peninsula and the islands of the Malay Archipelago; Australia; Cornwall, England, the Dutch East Indies, and Bolivia* Of the total output of 122,752 tons of tin produced m 1911, 61,712 tons were made from the Straits ore, 25,312 tons from the ore produced in Bolivia and 16,800 tons from Banka ore. Of the total
Oxides
quantity of tin produced about 78 per cent is said to come from stream tin and 22 per cent from ore obtained from veins. The quantity obtained from ore mined in the United States in igu included 61 tons from Alaskan stream tin and two tons from the tinstone mined in the Franklin Mountains near El Paso, Texas Mines have been opened in San Bernardino Co , California, and in the Black Hills, South Dakota, but they have not proved successful The mines at El Paso, Texas, are not yet fully developed, although they promise to be profitable in the near future The crystals are scattered through quartz veins and through a pink granite near the contacts with the veins The average composition of the ore is 2 per cent This is concentrated to a 60 per cent ore before being smelted The production during 1912 was 130 tons of stream tin from Buck Creek, Alaska This was valued at $124,800. In the following year 3 tons of cassitente ere shipped from Gaffney, S C The imports of tin into the United States during 1911 were 53,527 tons valued at more than $43,300,000
Enaction — The tin is extracted from the concentrated ore by the simple process of reduction Alternate layers of the ore and charcoal are heated together in a furnace, when the metal results This collects in the bottom of the furnace and is ladled or run out The crude metal is refined by remeltmg m special refining furnaces
Uses of the Metal — The metal tin is employed principally for coating other metals, either to prevent rusting or to pre\ent the action upon them of chemical reagents Tin plate is thin sheet iron covered with tin Copper for culinary purposes is also often co\ ered with this metal It is used also extensively in forming alloys with copper, antimony, bismuth and lead Among the most important of these alloys are bronze, bell metal, babbitt metal, gun metal, britanma, pewter and soft solder Its alloy, or amalgam, with mercury is used in coating mirrors. Several of its compounds also find uses m the arts Tin oside is an im- portant constituent of certain enamels The chlorides are used exten- sively in dyeing calicoes, and the bisulphide constitutes " bronze powder " or " mosaic gold," a powder employed for bronzing plaster, wood and metals
Rutile (Ti02)
Rutile is one of the oxides of the comparatively rare element titanium. It occurs commonly m dark brown opaque cleavable masses and in bril- liant black crystals
Pure rutile consists of 40 per cent 0 and 60 per cent TL Nearly all specimens, however, contain in addition some iron, occasionally as much
Descriptive Mineralogy
as 9 per cent or 10 per cent, which is probably due to the admixture of
and FeTiOs in solid solution
Rutile is perfectly isomorphous with cassiterite Its axial ratio is i : 6439 The pnncipal planes observed on its crystals are practically the same as those observed on cassiterite (Fig 80) Twins aie common, with P oo (101) the twinning plane (Fig 81 ) This twinning is often repeated, producing elbow-shaped groups (Fig 82), or by further repe-
FIG So.— Rutile Crystals with P, no (m), oo p oo , 100 (a), P oo , yoi (e), P, 111(5),
Fig 81
Fig 82
FIG 81 —Rutile Eightling Twinned about P oo (101) FIG 82 —Rutile Twinned about P oo (101) Elbow Twin
tition wheel-shaped aggregates (Fig 83) In another common law the twinning plane is 3? oo (301") (Fig 84) The angle in A iTx — 56° 52' The crystals are prismatic and even sometimes acicular in habit. Their prismatic planes are vertically striated
The cleavage of rutile is quite distinct parallel to oo P(no) and less so parallel to oo P oo (100)
The mineral is reddish brown, yellowish brown, black or bluish brown by leflected light and sometimes deep red by transmitted light, Many specimens are opaque but some are translucent to transparent.
Oxides
The latter are often pleochroic in tints varying between yellow and blood-red The streak is pale brown The hardness of the mineral is 6 to 6 5 and its density about 42 It is an electric nonconductor at ordinary temperatures Its refractive indices for yellow light are: 2 6030, €=2 8894.
Rutile is infusible and insoluble. Its reactions with beads of borax and microcosmic salt are usually obscured by the iron present When this metal is present only in small quantities the microcosmic salt bead is colorless while hot, but violet when cold, if it has been heated for some time in the reducing flame of the blowpipe
The most characteristic chemical reaction of rutile is obtained upon fusing it with sodium carbonate on charcoal, dissolving the fused mass in
Fig 83. Fig 84
FIG 83 —Rutile Cyclic Sixling Twinned about P (101)
FIG 84 — Rutile Twinned about 3? (301) Elbow Twin Forms °° P2, 210 (A),
and P °o , ioi (e)
an excess of hydrochloric acid and adding to the solution small scraps of tin Upon heating for some little time, the solution assumes a violet color. This is a universal test for the metal titanium
Some of the dark red and reddish brown massive varieties of rutile may be confounded with some varieties of garnet, which, however, are much harder. Its density, its infusibihty and the reaction for titanium serve to characterize the mineral perfectly
Pseudomorphs of rutile after hematite and after brookite and ana- tase have been described It often changes into ilmenite and sphene.
Syntheses. — By the reaction between TiCU and water vapor in a red- hot porcelain tube, crystals of rutile are formed. Twins are produced by submitting precipitated titanic acid in a mass of molten sodium tung- state to a temperature of 1000° for several weeks.
Occurrence and Origin —Rutile is often found as crystals embedded in limestone and m the quartz or f eldspar of granite and other igneous
174 Descriptive Mineralogy
rocks, as long acicular crystals m slates, and as grams in the rock known as nelsomte It occurs also as fine hair-like needles penetrating quartz, forming the ornamental stone " fleches d'amour," and as grains in the gold-bearing sand regions When primary it is probably always a product of magmatic processes, either crystallizing from a molten magma or being the result of pneumatolysis.
Localities — Handsome crystals of the mineral occur at Arendal, in Norway, in Tyrol, and at St Gothard and in the Binnenthal, Switzer- land In the United States large crystals have been obtained at Barre, Mass , at Sudbury, Chester Co , Penn ; at Stony Point, Alexander Co , N C , at Graves Mt , in Georgia, at Magnet Cove, in Arkansas, and in Nelson Co , Va. In the latter place it occurs in large quantity as crystals disseminated through a coarse granite rock The rock con- taining about 10 per cent of rutile is mined as an ore It constitutes the principal source of the mineral in the United States A second type of occurrence in the same locality is a dike-like rock, nelsomte, composed of ilmemte and apatite, in which the ilmemte is in places almost completely replaced by rutile
Uses — The mineral is not of great economic importance It is used in small quantity to impart a yellow color to porcelain and to give an ivory tint to artificial teeth. It is also used in the manufacture of the alloy ferro-titamum which is added to steel to increase its strength Recently the use of titamferous electrodes in arc lights, and the use of titanium for filaments in incandescent lamps ha\e been proposed Some of the salts of titanium are used as dyes and others as mordants Most of the ferro-titamum made m the United States is manufactured from titamferous magnetite
Production — The only rutile mined in the United States during 1913 came from Roseland, Nelson Co., Virginia. It amounted to 305 tons of concentrates containing about 82 per cent TiOs At the same time there were separated about 250 tons of ilmemte (see p 462)
Polianite (MnCI is usually in groups of tiny parallel crystals and as crusts of crystals enveloping crystals of manganite (MnO OH). Their axial ratio is i ' 6647 The color of the mineral is iron-gray. Its streak is black, its hardness 6-6 5 and density 4 99. It dissolves in HC1 evolv- ing chlorine It is distinguished from pyrolusite by its greater hardness and its lack of water The mineral is extremely rare, being found in measurable crystals only at Platten in Bohemia It occurs in pseudo- morphs after manganite at a number of other points m Europe and at a few points elsewhere, but in most cases it has not been dearly distin-
Oxides 175
guished from pyrolusite The rarity of its crystals is regarded by some mineralogists as being due to the fact that in most of its occurrences poliamte is colloidal (a gel)
Plattnerite (PbO2) is usually massive, but it occurs in prismatic crystals near Mullan in Idaho Their axial ratio is i : 6764 They are usually bounded by oo P oo (100), 3? oo (301), P oo (101), oP (ooi) and often IP (33 2) The mineral is found also in crusts Its color is iron-black and its streak chestnut-brown Its hardness is 5-5 5 and its density 86 It is brittle and is easily fusible before the blow- pipe, giving off oxygen and coloring the flame blue It yields a lead bead It is difficultly soluble in HNOs, but easily soluble in HC1 with evolution of chlorine. Plattnente is found at Leadhills and at Wanlock- head, Scotland, and at the " As You Like " Mine near Mullan, Idaho.
Pyrolusite
Pyrolusite is often the result of the alteration of the hydroxide, man- gamte, or of pohamte. The few measurable crystals that have been studied seem to indicate that their form is pseudomorphic after the hydroxide The change by which manganite may pass over into pyro- lusite is represented by the reaction 2MnO(OH)-f-0=2Mn02+H2O. Pyroiusite may be, however, only a slightly hydrated form of poliamte.
An analysis of a specimen from Negaunee, Mich., gave
MnO O CaO BaO SiOa Limomte HgO Total
79 46 17 48 18 38 18 .31 i 94 99 93
Pyrolusite, as usually found, is in granular or columnar masses, or in masses of radiating fibers It is a soft, black mineral with a hardness of only 2 or 2 5 and a density of about 4.8 Its luster is metallic and its streak black It is a fairly good conductor of electricity.
The reactions of this mineral are practically the same as those of pohanite and manganite (see p 191), except that only a small quantity of water is obtained from it by heating. Upon strong heating it yields oxygen, according to the equation 3Mn02=Mn3+3Q2-
The manganese minerals are easily distinguished from other minerals by the violet color they give to the borax bead and by the green prxjduct obtained when they are fused with sodium carbonate. Pyrolusite is distinguished from manganite by its physical properties, and from amte by its softness
176 Descriptive Mineralogy
Localities — -Pyrolusite is worked at Elgersberg, near Ilmenau in Thuringia, at Vorder Ehrensdorf in Moravia, at Flatten in Bohemia, at CartersviUe, Ga , at Batesville, Ark , and m the Valley of Virginia A manganiferous silver ore containing considerable quantities of pyro- lusite is mined in the Leadville district, Colorado, and large quan- tities of manganiferous iron ores are obtained in the Lake Superior region
Uses — Pyrolusite, together with the other manganese ores with which it is mixed, is the source of nearly all the manganese compounds employed in the arts Some of the ores, moreover, are argentiferous and others contain zinc From these silver and zinc are extracted The most important use of the mineral is in the iron industry. In this indus- try, however, much of the manganese employed is obtained from man- gamferous iron ores The alloys spiegeleisen and ferro-manganese are employed very largely in the production of an iron used m casting car wheels. It is extremely hard and tough The manganese minerals are also used in glass factories to neutralize the green color imparted to glass by the ferruginous impurities m the sands from which the glass is made They are also used m giving black, brown and violet colors to pottery and some of their salts are valuable mordants Pyrolusite, finally, is the principal compound by the aid of which chlorine and oxygen are pro- duced.
Production — The United States in 1912 produced about 1,664 tons of manganese ores, valued at $15,723, and all came from Virginia, South Carolina and California In previous years the ores had been mined also m Arkansas, Tennessee and Utah Moreover, there were imported into the country 300,661 tons, valued at $1,769,000 Nearly all of this was used in the manufacture of spiegeleisen The domestic product was used in the chemical industries largely in the manufacture of manganese brick Of the manganiferous iron ores about 818,000 tons were produced ui 1912 These were utilized mainly as ores of iron, though a large por- tion was used as a flux. The product of manganiferous silver ores aggre- gated about 48,600 tons, all of which was used as a flux for silver-lead ores. Nearly all of this came from Colorado In addition there were imported iron-manganese alloys valued at $3,935,000.
Anatase and BrooMte
As has already been stated, the compound Ti02 is trimorphous, one form being orthorhombic and the two others tetragonal Of the latter, one has already been described as rutile The other is anatase, or octa- hednte. The orthorhombic form is known as brookite Anatase and
Oxides 177
rutile are separated because of the difference in their axial ratios and in the habits of their crystals Both are ditetragonal bipyramidal, but a : c for rutile is i : 6439 and for anatase i . i 7771 Brookite is orthorhombic bipyramidal with a : b c- 8416 : i : .9444.
Both anatase and brookite have the same empirical composition, which is similar to that of rutile
Crystals of anatase are usually sharp pyramidal with the form P(in) predominating (Fig 85), blunt pyramidal with |P(ii3) or $P(ii7) predominating (Fig 86), or tabular parallel to oP(ooi) Twins are common in some localities, with P oo (101) the twinning plane. The angle in A iTiaBS82° 91'
The mineral is colorless and transparent, or dark blue, yellow, brown
Fig 86
FIG 85 — Anatase Crystal with P in (p)
oo P oo , 100 (a) and P GO , 101 (t)
or nearly black and almost opaque Its streak is colorless to light yellow. Its cleavage is perfect parallel to P and oP and its fracture conchoidal Its hardness is between 5 and 6 and its density is 3.9. This increases to 4 25 upon heating to a red heat, possibly due to its partial transformation into rutile The mineral is insoluble in acids except hot concentrated EkSO-i. It is a nonconductor of electricity. Its indices of refraction for yellow light are 2 5618, 2 4886
Brooktte crystals are usually tabular parallel to oo P 60 (too) and elongated in the direction of the c axis Nearly all crystals are striated in the vertical zone Although many forms have been identi- fied on them, by far the most common is P2(i22) In some cases this is the only pyramidal form present, as in the type known as arkanstie (Fig. 87) Twins are rare, with oo ¥2(210) the twinning plane. The angle in AiTi==:640 17'.
Descriptive Mineralogy
Brookite may be opaque, translucent or transparent Its color vanes from yellowish brown, through brownish red, to black (arkansite) Its streak is brownish yellow Its clea\age is imperfect parallel to oo Poo (101), and its fracture uneven or conchoidal Its hardness is 5-6 and density about 4, Upon heating its density increases to that of rutile Its refractive indices for yellow light are 2 5832, 2 5856, 7=2 7414 It fuses at about 1560°, and is insoluble in acids
The chemical properties of both brookite and anatase are similar to those of rutile They are distinguished from rutile by their physical properties and their crystallization
Both brookite and anatase alter to rutile
Syntheses —Upon heating TiFi with water vapor at a temperature
FIG §7— Brookite Crystals with coP, no (w), JP, 112 (z) and PsT, 122 (e) combination m and e is characteristic for \rkanbitc
The
below that of vaporizing cadmium, crystals of anatase are produced. If the temperature is raised above the point of vaporization of cadmium and kept below that of zinc, crystals of brookite result
Occurrence — Brookite and anatase occur as crystals on the walls of clefts in crystalline silicate rocks and in weathered phases of volcanic rocks. They are mainly pneumatolytic products, the production of the one or the other depending upon the temperature at which the TiCfe was deposited
Localities — Fine brookite crystals are found at St Gothard, in Switzerland, at Pregrattan, in the Tyrol, near Tremadoc, in Wales, at Miask, in Russia, and at Magnet Cove, Arkansas
Anatase crystals are less common than those of brookite but they occur at many points in Switzerland, especially in the Binnenthal, near Bourg d'Oisans, France, at many points in the Urals, Russia, in the diamond fields of Brazil, and at the brookite occurrences m Arkansas,
Chapter Vie
The Hydroxides
THE hydroxides, as has already been explained, may be looked upon as derivatives of water, m which only a portion of the hydrogen has been replaced. The group includes several minerals of economic importance, among which is the fine gem mineral opal All the hydroxides yield water when heated in a glass tube, but they do not yield it as readily as do salts containing water of crystallization
A few of the hydroxides may act as acids forming salts with metals Diaspore, for instance, is an hydroxide of aluminium A10-OH, or
/0-H
Al< , which appears to be able to form salts, at least, the chemical
composition of some of the members of an important group of minerals, the spinels, may be explained by regarding them as salts of this acid (seep 195)
Opal (Si02+Aq)
The true position of opal in the classification of minerals is somewhat doubtful From the analyses made it appears to be a combination of amorphous silica and water, or, perhaps, a mixture of silica in some form and a hydroxide of silicon The percentage of water present is variable. In some specimens it is as low as 3 per cent, while in others it is as high as 13 per cent The mineral is not known in crystals. It is probably a colloid, in which the water is, in part at least, mechanically held in a gel of SiCfe. It occurs only m massive form, in stalactitic or globular masses and in an earthy condition.
When pure the mineral is colorless and transparent Usually, how- ever, it is colored some shade of yellow, red, green or blue, when it is translucent or sometimes even opaque. The red and yellow varieties con- tain iron oxides and the green, prasopd, some nickd compound The play of color in gem opal is due to the interference of light rays reflected from the sides of thin layers of opal material with different densities from that of the mam mass of the mineral they traverse. The hardness of opal is 5 5-6 $ and its density about 2.1 Its refractive index for yellow light, 1.4401, It is a nonconductor of electricity.
180 Descriptive Mineralogy
The principal varieties of opal are
Precwus opal, a transparent variety exhibiting a delicate play of colors,
Fire opal, a precious opal in which the colors are quite brilliant shades of red and yellow,
Girasol, a bluish white translucent opal with reddish reflections,
Common opal, a translucent variety without any distinct play of colors,
Cachalong, an opaque bluish white, porcelain-like variety,
Hyalite, a transparent, colorless variety, usually m globular or botryoidal masses, and
Siliceous sinter, white, translucent to opaque pulverulent accumula- tions and hard crusts, deposited from the waters of geysers and other hot springs.
Tnpolite and infusorial earth are pulverulent forms of silica in which opal is an important constituent Tripoli is a light porous siliceous rock, supposed to have resulted from the leaching of calcareous material from a siliceous limestone Infusorial earth represents the remains of certain aquatic forms of microscopic plants known as diatoms
Flint and Chert are mixtures of opal, chalcedony and quartz
All vaneties of opal are infusible and all become opaque when heated When boiled with caustic alkalies some varieties dissolve easily, while others dissolve very slowly.
Syntheses — Coatings of material like opal have been noted in glass flasks containing hydrofluosilicic acid that had not been opened for several years Opal has also been obtained by the slow cooling of a solution of silicic acid in water.
Occurrence — The mineral occurs as deposits around hot springs It also forms veins in volcanic rocks and is embedded in certain lime- stones and slates, where it is probably the result of the solution of the siliceous spicules and shells of low forms of Me and subsequent deposi- tion It also results from the solution of the calcite from limestones containing finely divided silica
It is not an uncommon alteration product of silicates It seems to have been deposited from both cold and hot water
Localities. — Precious opal is found near Kashan, in Hungary, at Zimapan, Quaretaro, in Mexico, in Honduras, in Queensland and New South Wales, Australia, and in the Faroe Islands Common opal is abundant at most of these localities and is found also in Moravia, Bohemia, Iceland, Scotland and the Hebrides Hyalite occurs in small quantity at several places m New York, New Jersey, North Carolina,
Hydroxides 181
Georgia and Florida, and common opal, at Cornwall, Perm., and in Calaveras Co , California Common opal and vaneties exhibiting a little fire have recently been explored in Humboldt and Lander Counties, Nevada Siliceous sinter is deposited at the Steamboat Springs in Nevada and geysente (a globular form of the sinter) at the mouths of the geysers in the Yellowstone National Park
Uses — The precious and fire opals are popular and handsome gems Opahzed wood, i e , wood that has been changed into opal in such a manner as to retain its woody structure, is often cut and polished for use as an ornamental stone Infusorial earth, a white earthy deposit of microscopic shells consisting largely of opal material, possesses manv uses It is employed in the manufacture of soluble glass, polishing powders, cements, etc , and as the " body," which, saturated with nitro- glycerine, composes dynamite, Tripoli, a mixture of quartz and opal, is used as a wood filler, in making paint, as an abrasive and in the manufacture of filter stones. The principal sources of commercially valuable opal material in the United States are the opalized forest in Apache Co., Ariz , the infusorial earth beds at Pope's Creek and Dun- kirk, Md , various places in Napa Co , Cal , at Virginia City, Nev , and at Drakesville, N. J., and the tnpoh beds in the neighborhood of Stella, Mo , and the adjoining portion of Illinois
Production — The total quantity of infusonal earth and tnpoh mined during 1912 was valued at $125,446. The aggregate value of precious opal obtained in 1912 was $10,925. TluTcame from California and Arizona.
Brucite (Mg(OH)2)
Brucite is the hydroxide of magnesium. It is a white, soft mineral usually occurring in crystals or in foliated masses
Analyses of the mineral correspond very closely to the formula Mg(OH)2 which requires 41 38 per cent Mg, 27 62 per cent 0 and 31.00 per cent EkO, though they usually show the presence of small quantities of iron and manganese A specimen from Reading, Perm., yielded:
MgO FO3 MnO H2O Total
67.64 82 63 3° 92 I0° Oi
The crystallization of brucite is hexagonal (ditrigonal scalenohedral), a : c=i : 1.5208 The crystals are tabular in habit in consequence of the broad development of the basal plane oP(oooi). The other forms present are R(ioli), -(0441) and -fRCoiTj) (Fig. 88) The angle roll A 7ioi 97° 38'.
182 Descriptive Mineralogy
The cleavage of brucite is very perfect parallel to oP(ooi), and folia that may be split off are flexible The mineral is sectiie Its hardness is 2 5 and its density 2 4 Its color is white, inclining to bluish and greenish tints, and its luster pearly on oP Brucite is transparent to translucent It is pyroelectnc and a non- conductor of electricity Its refractive indices for red light are i 559 579
In the closed tube brucite, like other hy- droxides, yields water The mineral is infusi- ble When intensely heated, it glows After FIG 88 —Brucite Crystal heating, it reacts alkaline When moistened with oR, ocoi (<0, R, mfo cobalt mtrate solution and heated, it turns
Pmk the characterlstlc reaction for magnesium The pure mineral is soluble in acids
Brucite resembles m many respects gypsum, talc, diaspore and some micas It is distinguished from diaspore and mica by its hardness and from talc by its solubility in acids Gypsum is a sulphate, hence the test for sulphur will sufficiently characterize it
Synthesis — Crystals have been made by precipitating a solution of magnesium chloride with an alcoholic solution of potash, dissolving the precipitate by heating with an excess of KOH and allowing to cool
Occurrence and Origin — Brucite is usually associated with other magnesium minerals It is often found in veins cutting the rock known as serpentine, where it is probably a weathering product, and is some- times found in masses in limestone, especially near its contact with igneous rocks
Localities — It occurs crystallized in one of the Shetland Islands, at the Tilly Foster Iron Mine, Brewster, N Y , at Woods Mine, Texas, Perm , and at Fritz Island, near Reading, in the same State
Gibbsite (A1(OH)3)
Gibbsite, or hydrargillite, is utilized to some extent as an ore of alu- minium It occurs as crystals, in granular masses, in stalactites and in fibrous, radiating aggregates
Its theoretical composition demands 6541 per cent AkOs and 34.59 per cent H20 Usually, however, the mineral is mixed with bauxite (AlsO(OH)4) and in addition contains also small quantities of iron, magnesium, silicon and often calcium
Crystals are monodmic with a : b : 1=1.709 i : i 918 and £=85° 29!'. Their habit is tabular, Besides the basal plane, oP(ooi), the
Hydroxides 183
two most prominent forms are so Poo (I00) ancj aop(IIOi Thus the plates have hexagonal outlines They ha\e a perfect cleavage parallel to the base Twinning is common, oP(ooi) the twinning plane
The mineral has a glass} luster except on the basal plane where its luster is pearly It is transparent or translucent, Tvhite, pink, green or gray Its streak is light, its hardness is 2-3 and specific gravity 2 35 It is a nonconductor of electricity. Its refractue indices are a
15347, 7=15577
When heated before the blowpipe the mineral exfoliates, becomes white, glows strongly but does not fuse Upon cooling the heated mass is hard enough to scratch glass The mineral dissolves slowly but com- pletely m hot HC1 and in strong HaSOi, and gives a blue color when moistened with Co(NOs)2 solution and heated.
Gibbsite resembles most closely bauxite, from which it is distin- guished principally by its structure It differs from umelhte (p. 287), which it also sometimes resembles, in the absence of phosphorus.
Syntheses — Crystals of gibbsite have been made heating on a water bath a saturated solution of Al(OH)s in dilute ammonia until all of the ammonia evaporates, and also by gradually precipitating the hydroxide from a warm alkaline solution by means of a slow stream ofCO2
Occurrence — The mineral rarely occurs in pure form It is found in veins and in cavities in various schistose and igneous rocks. It is prob- ably a weathering product of aluminous silicates.
Localities — Gibbsite has been reported as existing in small quantities at various points m Europe, near Bombay, India, and at several places in South America and Africa. In the United States it occurs at Rich- mond, Mass , at Union Vale, Dutchess Co , N Y., and mixed with bauxite at several of the occurrences of this mineral (see page 186).
Uses. — It is mined with bauxite as a source of aluminium.
Limonite (Fe4O3(OH)b)
Limomte is an earthy or massrve reddish brown mineral whose composition and crystallization are but imperfectly known It is an important iron ore called in the trade " brown hematite "
The analyses of limomte range between wide limits, largely because of the great quantities of impurities mixed with it. The formula de- mands 59 8 per cent Fe, 25 7 per cent 0 and 14.5 per cent water, but the percentages of these constituents found in different specimens only approximately correspond to these figures Many mineralogists regard
Descriptive Mineralogy
Fte 89 — Limonite Stalactites in Silverbow Mine, Butte, Mont (After W H Weed )
Era 90— Botiyoidal Lunomte
Hydroxides 185
limomte as colloidal goethite (FeO OH with one molecule or more of EfeO, depending upon temperature The principal impurities are clay, sand, phosphates, silica, manganese compounds and organic matter The great variety of these is thought to be due to the lact that the hmonite, like other gels, possesses the po\\er of absorbing compounds from their solution, so that the mineral is in reaht> a mixture of col- loidal iron dro\ide and anous compounds which differ in different occurrences
The mineral occurs in stalactites (Fig 8g\ in botiyoidd forms tFig 90), in concretionary and clay-like masses and often as pseudomorphs after other minerals and after the roots, lea\es and stems of trees
Limomte is brown on a fresh fracture, though the surface of mc.ny specimens is co\ ered \uth a black coating that is so lustrous as to appear varnished Its streak is yellowish brown Its hardness is a little er 5 and its density about 3.7. The mineral is opaque and its luster is dull, silky or almost metallic according to the ph\sical conditions of the spec- imen. Its index of refraction is about 25 It is a nonconductor of electricity
The varieties recognized are. compact, the stdactitic and other fibrous forms, ocherous, the brown or yellow ecrthy, impure variety, bog iron the porous variety found in marshes, pseudomorphing leaves, etc , and brown clay ironstone, the compact, massive or nodular form.
In its chemical properties limomte resembles goer tie, from hich it can be distinguished only with great difficulty except when the latter is in crystals From uncrystalhzed varieties of goethite it can usually be distinguished only by quantitative analysis, although in pure specimens the streaks are different
Occurrence and Origin. — Limonite is the usual result of the decom- position of other iron-bearing minerals Consequently, it is often found in pseudomorphs. In almost all cases 'ahere large beds of the ore occur the material has been deposited from ferriferous water nch in organic substances One of the commonest types of occurrence is " gossan." In the production of this type of ore, those portions of veins carrying ferruginous minerals are oxidized under the influence of oxygen-bearing waters, forming a layer composed largely of limonite which covers the upper portion of the veins and hides the original vein matter Gossan ores denved from chalcopynte and pynte are common in all regions in which these minerals occur Another type of limonitic ore comprises those found in clays derived from limestones by weathering In such deposits the ore occurs as nodules and in pockets in the day. Ores of
186 Descriptive Mineralogy
this type are common in the valleys within the Appalachian Moun- tains Bog iron ores occur in swamps and lakes into which ferruginous solutions drain The iron may come from pynte or iron silicates in the drainage basins of the lakes or swamps When carried down it is oxi- dized by the air and sinks to the bottom
Localities —The mineral occurs abundantly and in many different localities The most important American occurrences are extensive beds at Salisbury and Kent, Conn , at many points in New Jersey, Pennsylvania, Michigan, Tennessee, Alabama, Ohio, Virginia and Georgia
Uses — Although containing less iron than hematite, on account of its cheapness, and the ease with which it works in the furnace, brown hematite is an important ore of this metal The earthy \arieties are used as cheap paints
Production —The yield of the United States " brown hematite " mines for 1912 was a little over 1,600,000 tons Of this amount the largest yields were
Alabama 749,242 tons
Virginia 398,833 tons
Tennessee 171,130 tons
The quantity of ocher produced in the United States during the same year amounted to about 15,269 tons, valued at $149,289 Most of it came from Georgia In addition, 8,020 tons were imported. This had a value of $148,300
Bauxite (A12O(OH)4)
Bauxite, or beauxite, like hmomte, is probably a colloid At any rate it is unknown in crystals Until recently it possessed but little value It is now, however, of considerable, importance as it is the prin- cipal source of the aluminium on the market
The mineral is apparently an hydroxide of aluminium with the for- mula Al20(OH)4 or Al20s 2H20 m which 26 i per cent is water and 73 9 per cent alumina (Al20s), but it may be a colloidal mixture of the gibbsite and diaspore (p 190) molecules, or of various hydroxides, since its analyses vary within wide limits A sample of very pure material from Georgia gave on analysis
A12O3 Fe203 Si02 Ti02 H2O
62 46 81 4 72 23 31
Hydroxides
1St
Bauxite occurs in concretionan grains (Fig 91*, m earthy, clay-like forms and massu e, usually in pockets or lenses in cia\ resulting from the weathering of limestones or of s\emte It is \\hite when pure, but as usually found is yellow, gra> , red or brown in color, is translucent to opaque and has a colorless or very light streak. Its density is 2 55 and its hardness anywhere between i and 3 Its luster is dull. It is a nonconductor of electricity
Before the blowpipe bauxite is infusible In the closed'tube it yields
FEG. 91 — Pisohtic Bauxite, from near Rock Run, Cherokee Co , Ala.
water at a high temperature. Its powder when intensely heated with a few drops of cobalt nitrate solution turns blue. The mineral is with difficulty soluble in hydrochloric acid.
Occurrence and Origin —Bauxite in some cases may be a deposit from hot alkaline waters, but in Arkansas it is a residual eathenng product of the igneous rock, syenite. It occurs in beds associated with corundum, clay, gibbsite and other aluminium minerals.
Localities. — Large deposits of the ore occur at Baux, near Aries, France, near Lake Wochem, in Carniola, in Nassau; at Antrim, Ire- land, in a stretch of country between Jacksonville, Fla., and Carters-
188 Descriptive Mineralogy
ville, Ga , in Saline and Pulaski Counties, Ark , m Wilkinson Co , Ga , and near Chattanooga, Tenn
Preparation —The ore is mined by pick and shovel, crushed and washed It is then, in some cases, dried and broken into fine particles The fine dust is separated from the coarser material, and the latter, which comprises most of the ore, is heated to 400° This changes the iron compounds to magnetic oxide which is separated electro-mag- neticaJly The concentrate contains about 86 per cent of AfaOb This is then purified and dissolved in a molten flux, in some cases cryolite, and is subjected to electrolysis The quantity of aluminium made in the United States during 1912 was over 65,600,000 Ib , valued at about $17,000,000. The value of the aluminium salts produced was about $3,000,000.
Uses — Bauxite (or more properly the mixture of bauxite and gibbs- ite) is practically the only commercial ore of aluminium which, on account of its lightness and its freedom from tarnish on exposure, has become a very popular metal for use in various directions It is em- ployed in castings where light weight is desired and in the manufacture of ornaments and of plates for interior metallic decorations It is also employed in the steel industry, and, in the form of wire, for the trans- mission of electricity The mineral is also used in the manufacture of aluminium salts, in making alundum (artificial corundum), and bauxite brick for lining furnaces, and in the manufacture of paints and alloys.
Production — The bauxite mined in the United States during 1912 amounted to about 159,865 tons valued at $768,932, the greater portion coming from Arkansas This is about two-thirds the value of the pro- duction of the entire world
Psilomelane
Psilomelane is probably a mixture of colloidal oxides and hydroxides of manganese in various proportions In most specimens there is a notable percentage of BaO or £20 present, and m others small quantities of lithium and thallium. The barium and potassium components are thought to have been absorbed from their solutions
The substance occurs in globular, botryoidal, stalactitic, and massive forms exhibiting, in many instances, an obscure fibrous structure Its color is black or brownish black and its streak brownish black and glistening. Its hardness is 5 5-6 and specific gravity 4.2
Psilomelane is infusible before the blowpipe, m some cases coloring the flame green (Ba) and in others violet (K). With fluxes it reacts for
Hydroxides 189
manganese. In the closed tube it yields water. It is soluble in HC1 with evolution of chlorine
It is distinguished from most other manganese oxides and hydroxides by its greater hardness.
Occurrence — Psilomelane occurs in veins associated with pyrolusite and other manganese compounds, as nodules in clay beds, and as coatings on many mangamferous minerals In all cases it is probably a product of weathering
Locahties — It is found in large quantity at Elgersburg in Thuringia; at Ilfeld, Harz, and at various places in Saxony. In the United States it occurs with pyrolusite and other ores of manganese at Brandon, Vt ; in the James River Valley, and the Blue Ridge region of Virginia; in northeastern Tennessee; at Cartersville, Georgia, at Batesville, Arkan- sas, and in a stretch of country about forty miles southeast of San Francisco, California. At many of these points it has been mined as an ore of manganese
Wad
Wad is a soft, earthy, black or dark brown aggregate of manganese compounds closely related to psilomelane
It occurs in globular, botryoidal, stalactitic, flaky and porous masses, which, m some cases, are so light that they float on water. It also occurs in fairly compact layers and coats the surfaces of cracks, often forming branching stains, known as dendntes
Wad contains more water than psilomelane, of which it appears often to be a decomposition product. More frequently it results from the weathering of manganiferous iron carbonate It is particularly abundant in the oxidized portions of veins containing manganese car- bonates and silicates
Wad is easily distinguished from all other soft black minerals, except pyrolusite by the reaction for manganese, and from all other manganese compounds, except pyrolusite, by its softness From pyrolusite it is distinguished by its content of water.
Localities— It occurs in most of the localities at which other man- ganese compounds are found.
Diaspore Group
The diaspore group comprises the hydroxides of aluminium, iron and manganese, possessing the general formula R'"O(OH). They are regarded as hydroxides in which one of the hydrogens in BfeO is replaced by the group R/7/0, thus: H— O— H, water, A10— 0— H, diaspore These
Descriptive Mineralogy
three compounds from a chemical viewpoint, may be looked upon as the acids whose salts comprise the spinel group of minerals, which includes among others the three important ore minerals magnetite, chromite and frankhnite Of the three members of the diaspore group the manganese and iron compounds are valuable ores All are orthorhombic, in the rhombic bipyramidal class.
Diaspore (AIO(OH))
Diaspore is found in colorless or light colored crystals, in foliated masses and in stalactitic forms
Its composition is theoretically 85 per cent AbOs and 15 per cent
Fro 92 — Diaspore Crystals oo P So , oio (fi) , oo Pj , 130 (s) , GO P, no (m), 210 (A), PS5, on (e), ?2, 212 (s), ooPl, 120 (/), P<j, 150
HgO, though analyses show it to contain, in addition, usually, some iron and silicon A specimen from Pennsylvania yielded.
A1203
H20
Fe20s
Si02 Total i 53 100 44
Other specimens approach the theoretical composition very closely
In crystallization the mineral is orthorhombic (rhombic bipyramidal class), with a b . 9372 . i : 6039 The crystals are usually pris- matic, though often tabular parallel to oo P 56 (oio) The principal planes observed on them are oo Poo (oio), a series of prisms as ooP(no), oo Pa (210), °oP3(i3o), the dome PQ&(OII) and several pyramids (Fig. 92) The planes of the prismatic zone are often ver- tically striated The angle no A i Io-86° if
The cleavage of diaspore is very distinct parallel to the brachy- pmacoid. Its fracture is conchoidal and the mineral is very brittle, Its hardness is about 6 5 and density 3 4 The luster of the mineral is vitreous, except on the cleavage surface, where it is pearly. Its color
Hydroxides 191
varies widely, though the tint is always light and the streak colorless The predominant shades are bluish white, grayish white, yellowish or greenish white The mineral is transparent or translucent It is a nonconductor of electricity Its refractive indices for yellow light are 1702, j8=i 722, 7 1 750
In the closed tube diaspore decrepitates and gives off water at a high temperature It is infusible and insoluble in acids. When moistened with a solution of cobalt nitrate and heated it turns blue, as do all other colorless aluminium compounds
In appearance, diaspore closely resembles Irucite (Mg(OH)s), from which it may be distinguished by its greater hardness and its aluminium reaction with cobalt nitrate
Synthesis — Crystal plates of diaspore have been made by heating at a temperature of less than 500°, an excess of amorphous AfeQs in sodium hydroxide, enclosed in a steel tube At a higher temperature corundum resulted.
Occurrence — Diaspore occurs as crystals implanted on corundum and other minerals, and on the walls of rocks in which corundum is found It is probably in most cases a decomposition product of other aluminium compounds
Localities — In Ekaterinburg, Russia, it is associated with emery. At Schemnitz, Hungary, it occurs in veins It is found also in the Canton of Tessin, in Switzerland, at various places in Asia Minor, and on the emery-bearing islands of the Grecian Archipelago. In the United States it is associated with corundum, at Newlin, Chester Co , Penn , with emery at Chester, Mass , at the Culsagee corundum mine, near Franklin, N C , and at other corundum mines in the same State.
Manganite (MnO(OH))
Manganite usually occurs in groups of black columnar or prismatic crystals and in stalactites.
The formula MnO(OH) requires 27 3 per cent 0, 62 4 per cent Mn and 10 3 per cent water, or 89 7 per cent MnO and 10 3 per cent water. In addition to these constituents, the mineral commonly contains also some iron, magnesium, calcium and often traces of other metals. An analysis of a specimen from Langban, in Sweden, yielded:
Mn2O3 Fe203 MgO CaO H2O Total 88 51 23 i 51 62 9 80 100 67
The orthorhombic crystals of the mineral have an axial ratio a : i : c 8441 : i : ,5448 The crystals are nearly all columnar with a series
Descriptive Mineralogy
of , among which are oo Pio) and oo P(uo), and the two lateral pinacoids oo P 06 (oio) and 8 P a (100) terminated by oP(ooi) or by the domes P 06 (on), P 06 (101), and pyramids (Figs 93 and 94) Cru- ciform and contact twins, with the twinning plane P oo (on), are not uncommon (Fig 95) The prismatic surfaces are vertically striated and the crystals are often in bundles The angle no A iTo=8o° 20'
Cleavage is well defined parallel to oo P 06 (oio) and less perfectly developed parallel to ooP(no) The fracture is uneven The luster of the mineral is brilliant, almost metallic Its color is iron-black and its streak reddish brown or nearly black It is usually opaque but in very thin splinters it is sometimes brown by transmitted light. Its hard- ness is 4 and density about 4 3. The mineral is a nonconductor of electricity Mangamte yields water in the closed tube and colors the borax bead amethyst m the oxidizing flame of the blowpipe. In the reducing flame, upon long-continued heating, this color disappears The mineral dis- solves in hydrochloric acid with the evolution of chlorine. It is dis-
FIG 93 — Mangamte Crystal with ooP, no(w), oP,ooi (c) and P 55 , ioi
FIG 94 — Group of Prismatic Mangamte Crystals from Lfeld, Hare.
tinguished from other manganese minerals by its hardness and crystal- lization.
By loss of water mangamte passes readily into pyrolusite (MnCfe). It also readily alters into other manganese compounds
Synthesis.— Upon heating for six months a mixture of manganese chloride and damn caarbonate fine crystals like those of mangamte
Hydroxides 193
have been obtained Their composition, howe\er, was that of haus- manmte, indicating that \\hile mangamte was produced, it was changed to hausmanmte during the process.
Occurrence, Localities and Origin — Man- gamte occurs in veins in old volcanic rocks, and also in limestone It is found at Ilfeld in the Harz, at Ilmenau in Thurmgia, and at Langban in Sweden, in handsome cns- tals In the United States it occurs at the Jackson and the Lucie iron mines, Xegaunee,
Mich , and in Douglas Co , Colo It is
, , , . A : „ FIG 05— Manoamte Crvstal
also abundant at arlous places m New Tvvmned abjut P('QII
Brunswick and Nova Scotia In all cases The torms are P notmj, it is a residual product of the weathering of =cP3,i2o./;andP3 31315) manganese compounds.
Uses — Mangamte is used in the production of manganese compounds. As mined it is usually mixed with pyrolusite, this being the most im- portant portion of the mixture
Goethite (FeO(OH))
This mineral, though occasional!}- found m blackish brown crystals, usually occurs in radiated globular and botryoidal masses Analyses of specimens from Maryland, and from Lostwithiel, in Cornwall, gave-
Fe20s Mn2Q3 H2O SiCb Total
Maryland 86 32 10 So 2 88 too oo
Lostwithiel 89 55 16 10 07 28 100 06
The formula FeO(OH) demands 89.9 per cent Fe2Qs and 10 i per cent H2O or 62.9 per cent Fe, 27 o per cent 0 and 10 i per cent HaO
Like diaspore and mangamte, goethite is orthorhornbic, its axial ratio being a : b : c 9185 : i : .6068 Its crystals are prismatic or acicular with the prisms plainly striated vertically The forms observed are commonly oo P 06 (oio), QO PS(2io\ oo P(no), P 06 (on) and P(rii). The angle no A 1*10=85° 8'.
The deavage of goethite is perfect parallel to oo P 06 (oio) and its fracture uneven Its hardness is 5 and density about 4.4. Its color is usually yellowish, reddish or blackish brown and its luster almost metallic In thin splinters it is often translucent with a blood-red color and a refractive index of about 2 5 Its streak is brownish yellow. It is an electric nonconductor.
194 Descriptive Mineralogy
The chemical reactions of the mineral are about the same as those of hematite, except that it yields water when heated in the closed tube By this reaction it is easily distinguished from the fibrous varieties of hematite, as it is also by its streak
Synthesis — Needles of goethite are produced by heating freshly precipitated iron hydroxide for a long time at 100°
Occurrence and Localities — Goethite is usually associated with other ores of iron, especially in the upper portion of veins, -where it is produced by weathering. It is found near Siegen in Nassau, near Bristol and Clifton, England, and in large, fine crystals at Lostwithiel and other places in Cornwall
In the United States it occurs in small quantity at the Jackson and the Lucie hematite mines in Negaunee, Mich , at Salisbury, Conn , at Easton, Penn , and at many other places
Uses — Goethite is used as an ore of iron, but in the trade it is classed with limomte as brown hematite
Chapter Dc The Alu3Iixates, Ferrites, Chromites \Xd Maxg \Xites
MOST of these compounds are salts of the comparative!} uncommon acids HA1O2, HFeOo and HCrCb, \\hich may be regarded as metaacids derived from the corresponding normal acids by the abstraction of water, thus. HsAlOs— H2O=HAlOo There are onh a few minerals belong- ing to the group but they are important One, magnetite, is an ore of iron, another, chronute, is the principal ore of chromium and two others are utilized as gems Most of them are included in the mineral group known as the spmels (Compare p 189 )
That there is a manganese acid corresponding to the metaacids of AI, Fe and Cr is indicated by the fact that in some of the spinels manganese replaces some of the fernc iron, as, for example, in frankhmte. This suggests that this mineral is an isomorphous mixture of a metafernte and a salt of the corresponding manganese acid (HMnCb) This may be regarded as derived from the hydroxide, MnfOH)s, by abstraction of H2O, thus- H3Mn03-H2CMHMnO.>. But there are other man- ganous acids Normal manganous acid is MnfOH), or H4Mn(>4 If from this one molecule of water be abstracted, there remains H2InOs, the metamanganous acid The manganous salt of the normal acid, Mn2MnQi, occurs as the mineral, hausmannite, and the corresponding salt of the metaacid, MnMnOs, as the mineral, braunite.
Spinel Group
The spinels are a group of isomorphous compounds that may be regarded as salts of the acids AIO(OH), MnO(OH), CrO(OH) and FeO(OH), in which the hydrogen is replaced by Mg, Fe and Cr.
Al— 0— CX Thus, spinel, Mg- AfeQ* may be regarded as yMg, magnetite,
Fe— 0— Ov Cr— O-Ov
Fe3O4, as II >Fe; clromite, FeCx&O*, as )>Fe, and
Fe-O-(X Cr-O-CK
(Fe Mn)-O-<X
frankhmte, as I I y>(Zn-Mn Fe). Chemical compounds of
(Fe Mn)-0-CK
Descriptive Mineralogy
this general type are fairly numerous, but only a few occur as minerals The most important are the three important ores mentioned above, spinel is of some value as a gem btone
The spinels crystallize in the holohedral divi- sion of the isometric system (hexoctahedral class), in well defined crystals that are usually combina- tions of 0(ui) and ooO(no), with the addition on some of ooQoo (100), 303(311), 202(211), 50(531), etc Contact twins are so common with 0 the twinning plane, that this type of twinning is often referred to as the spinel twinning (Fig 96).
Fig 96
Spinel Twin
The complete list of the known spinels is as follows.
Spinel
Ceylomte (pleonaste)
CJdorspinel
Picotite
Hercynite
Gahmte
Dysluite
Krwttomte
Magnetite
Magnesiofernte
Frankhmte
Jacobsite
Chromite
Mg(A102)2
(Mg Fe)(A102)2
Mg((Al Fe)02)2
(Mg Fe)((Al Fe-Cr)02)2
Fe(A102)2
Zn(A102)2
(Zn Fe Mn)((Al Fe)02)2
(Zn Fe Mg) ((Al Fe)O2)2
Fe(Fe02)2
Mg(Fe02)2
(Fe ZnMn)((Fe Mn)O2)2
(Mn Mg)((Fe Mn)02)2
(Fe Mg)(Cr Fe)02)2
Spinel (Mg(AlO2)2)
Ordinary spinel is the magnesian alummate, which, when pure, con- tains 28 3 per cent MgO and 71 7 per cent AfeOa Usually, however, there are present admixtures of the other isomorphs so that analyses often indicate Fe, Al and Cr
The mineral usually occurs in isolated simple crystals, rarely in groups The forms observed on them are 0(m), ooO(no) and 303(311), and rarely oo 0 oo (100) (Fig 97)
The pure magnesium spinel is colorless or FlG 97— Spinel Crystal some shade of pink or red, brown or blue, and J'Q (r£)"° is usually transparent or translucent, though an 3 3' 3I1 opaque varieties are not rare Its streak is white It possesses a glassy
Aluminates, Ferrites, Etc 197
luster, and a conchoidal fracture, but no distinct cleavage Its hard- ness is 8 and its density 3 5-3 6 Its refractive indices \ary with the color n for yellow light is i 7150 for red spinel and i 7201 for the blue variety.
The mineral is infusible before the blowpipe and is unattacked by acids It yields the test for magnesia with cobalt solution
Spinel is easily distinguished from most other minerals by its cns- tallization and hardness It is distinguished from pale-colored garnet by its blowpipe reactions, especially its infusibility, and its failure to respond to the test for Si02
The best known varieties are:
Precious spinel, which is the pure magnesian aluminate. It is trans- parent and colorless or some light shade of red, blue or green. The bright red variety is known as ruby spinel and is used as a gem Its color is believed to be due to the presence of chromium oxide It is easily distinguished from genuine ruby by the fact that it is not doubly refracting and not pleochroic.
The best ruby spinels come from Ceylon, where they occur loose in sand associated with zircon, sapphire, garnet, etc.
Common spinel differs from precious spinel m that it is translucent. It usually contains traces of iron and alumina.
Both these varieties of spinel occur in metamorphosed limestones and crystalline schists.
Syntheses — The spinels have been made by heating a mixture of AkOs and MgO with boracic acid until fusion ensues, and by heating Mg(OH)2 with AlCls in the presence of water vapor
Origin — Spinel has been described as an alteration product of corun- dum and garnet It is also a primary component of igneous rocks and a product of metamorphism in rocks nch in magnesium
Uses — Only the transparent ruby spinels have found a use. These are employed as gems
Ceylonite, or pleonaste, is a spinel in which a portion of the Mg has been replaced by Fe, i e , is an isomorphous mixture of the magne- sian and iron aluminates, thus ((Mg Fe)(AlO2)2) It is usually black or green and translucent, and has a brownish or dark greenish streak and a density 5-3 6
The analysis of a sample separated from an igneous rock in Madison Co , Mont., gave,
A12O3 FeO MgO CraOs Fe MnO CaO SiOa Total 62 09 17 56 15 61 2 62 2 10 tr 16 55 100 69
198 Descriptive Mineralogy
Ceylomte occurs in igneous rocks m the Lake Laach region, Germany, and m the Piedmont district, Italy and elsewhere, m meta- morphosed limestones at Warwick and Amity, N Y , m the limestone blocks enclosed in the lava of Vesuvius, and m dolomite metamor- phosed by contact action at Monzoni, Tyrol
Picotite, or chrome spinel, is a \anety intermediate between spinel proper and chromite Its composition may be represented by the formula (Mg Fe)((Al Fe Cr)O2)2 It occurs only m small crystals in basic igneous rocks and in a few crystalline schists Density i
Magnetite (Fe(FeO2)2)
Magnetite, the ferrous fernte, the empirical formula of which is FesO-i, is a heavy, black, magnetic mineral which is utilized as one of the ores of iron
The pure mineral consists of 72 4 per cent Fe and 27 6 per cent 0 Most specimens, however, contain also some Mg and many contain small quantities of Mn or Ti A selected sample of magnetite from the Eliza- beth Mine, Mt Hope, New Jersey, analyzed as follows
Fe2O3 FeO Si02 Ti02 A1203 MgO CaO Other Total 65 26 30 20 i 38 i 09 55 10 68 73 99 99
Magnetite occurs in crystals that are usually octahedrons or dodeca- hedrons, or combinations of the two , Other forms are rare Twins are common The mineral occurs also as sand and in granular and structureless masses When the dodecahedron is present, its faces are fre- quently striated parallel to the edge between ooO(no) and 0(ui) (Fig 98)
Magnetite is black and opaque and its streak FIG 98 —Magnetite is black It has an uneven or a conchoidal f rac- Crystal, with w o ture, but no distinct cleavage Its hardness is (llo) and ° (l3CI) S.SanddeM1ty49-5* It is strongly attracted f™* by a magnet and in many instances it exhibics and in polar magnetism
The mineral is infusible before the blowpipe Its powder dissolves slowly in HC1, and the solution reacts for ferrous and ferric iron
Magnetite is easily recognized by its color, magnetism, and hardness
The mineral weathers to lunomte and hematite and occasionally to the carbonate, sidente,
Aluminates, Ferrites, Etc. 199
Syntheses. — Crystals have been made by cooling iron-bearing silicate solutions, treating heated ferric hydroxide HC1, and by fusing iron oxide and borax with a reducing flame
Occurrence end Ongm. — The mineral occurs as a constituent of many igneous rocks and crystalline schists, and in lenses embedded in rocks of many kinds It also constitutes veins cutting these rocks and as irregular masses produced the deh\ dration and deoxidation of hematite and limomte under the influence of metamorphic processes. It occurs also as little grains among the decomposition products of iron-bearing silicates, such as olmne and hornblende.
The larger masses are either segregations from igneous magmas or deposits from hot solutions and gases emanating from them.
Localities — The localities at \\hich magnetite has been found are so numerous that only those of the greatest economic importance may be mentioned here. In Norway and Sweden great segregated deposits are \\orked as the principal sources of iron in these countries. In the United States large lenses occur in the limestones and siliceous crys- talline schists in the Adirondacks, New York, and in the schists and granitic rocks of the Highlands in New Jersey Great bodies are mined also at Cornwall, and smaller bodies at Cranberry, and in the Far West
Extraction — The magnetite is separated from the rock with which it occurs by crushing and exposing to the action of an electro-magnet.
Production — The total amount of the mineral mined m the United States during 1912 was 2,179,500 tons, of which 1,110,345 tons came from New York, 476,153 tons from Pennsylvania, and 364,673 tons from New Jersey.
FrankEnite ((Fe-Zn Ua)((Fe-Hn)O2)2)
Franklinite resembles magnetite in its general appearance. It is an ore of manganese and zinc
It differs from magnetite m containing Mn in place of some of the ferric iron in this mineral and Mn and Zn in place of some of its ferrous iron. Since it is an isomorphous mixture of the iron, zinc and manganese salts of the iron and manganese acids of the general formula R"'0(OH), its composition varies within wide limits The franklinite from Mine Hill, N. J , contains from 39 per cent to 47 per cent Fe, 10 per cent to 19 per cent Mn and 6 per cent to 18 per cent Zn A specimen from Franklin Furnace, N J., contained,
Fe203 MnO ZnO MgO CaO SiOa HsO Total 66 58 9 96 so 77 34 -43 -72 -71 99-5*
200 Descriptive Mineralogy
Its crystals are usually octahedrons, sometimes modified by the do- decahedron and occasionally by other forms The mineral occurs also in rounded grams, in granular and in structureless masses
It is black and lustrous and has a dark brown streak Its fracture and cleavage are the same as for magnetite It is only very slightly magnetic It has a hardness of 6 and a density of 5 15
The mineral is infusible before the blowpipe When heated on charcoal it becomes magnetic When fused with Na2COa in the oxidizing flame it gives the bluish green bead characteristic of manganese Its fine powder mixed with Na2COa and heated on charcoal yields the white coating of zinc oxide which turns green when moistened with Co(N03)2 solution and again heated
Franklinite is distinguished from most minerals by its color and crys- tallization and from magnetite and clromite by its brown streak and by its reactions for Mn and Zn It is also characterized by its associa- tion with red zmcite and green or pink willemite (p 306)
Synthesis — Crystals of franklmite have been made by heating a mixture of FeCla, ZnCb and CaO (lime)
Occurrence and Origin — Franklimte occurs at only a few places Its most noted localities are Franklin Furnace and Sterling Hill, N J , where it is associated in a white crystalline limestone with zmcite, willemite and other zinc and manganese compounds The deposit is supposed to have been produced by the replacement of the limestone through the action of magmatic waters and vapors.
Uses. — The mineral is utilized as an ore of manganese and zinc The ore as mined is crushed and separated into parts, one of which consists largely of franklmite This is roasted with coal, when the zinc is driven off as zinc oxide The residue is smelted in a furnace producing spiegeleisen, which is an alloy of iron and manganese used in the man- ufacture of certain grades of steel
Production — The quantity of this residuum produced in 1912 was 104,670 tons, valued at $314,010
Chromite (Fe(CrO2)2)
Chromite, or chrome-iron, is the principal ore of chromium. It resembles magnetite and frankhnite in appearance It occurs in iso- lated crystals, in granular aggregates, and in structureless masses.
Chemically, it is a ferrous salt of metachromous acid, of the theoret- ical composition Cr20a=68 per cent and FeO=32 per cent, but it usually contains also small quantities of AlOa, CaO and MgO An analysis of
Aluminates, Ferrites, Etc 201
a specimen from Chorro Creek, California, after making corrections for the presence of some serpentine, yielded
Cr203 A1203 Fe203 FeO MgO MnO Total
56 96 12 32 3 81 12 73 14 02 16 100 oo
Its crystals are usually simple octahedrons, but they are not as common as those of the other spinels
Its color is brownish black and its streak brown It has a conchoidal or uneven fracture and no distinct clea\age It is usually nonmag- netic, but some specimens slight magnetism because of the ad- mixture of the isomorphous magnetite molecule Its hardness is 5 5 and its density 4 5 to 4 8
The mineral is infusible before the blowpipe It gives the chromium reaction with the beads If its powder is fused with niter and the fusion treated with water, a yellow solution of KoCrO4 results When fused with NagCOs on charcoal it yields a magnetic residue.
Chromite is easily distinguished from all other minerals but ptco- tite by its crystallization and its reaction for chromium. It is distin- guished from picotite by its inferior hardness and its higher specific gravity.
Synthesis — Crystals have been made by fusing the proper constit- uents with boric acid and after fusion distilling off the boric acid.
Occurrence and Origin — Chromite occurs principally in olivine rocks and in their alteration product — serpentine The mineral is found not only as crystals embedded in the rock mass, but also as nodules in it and as veins traversing it It is probably in all cases a segregation from the magma producing the rock In a few places the mineral occurs in the form of sand on beaches
Localities — It is widely spread through serpentine rocks at many places, notably in Brussa, Asia Minor; at Banat and elsewhere in Norway; at Solnkive, in Rhodesia, in the northern portion of New Caledonia, at various points in Macedonia, in the Urals, Russia; in Beluchistan and Mysore, India
In the United States the mineral is known at several points in a belt of serpentine on the east side of the Appalachian Mountains, and at many points in the Rocky Mountains, the Sierra Nevada and the Coast Ranges It has been mined at Bare Hills, Maryland, in Siskiyou, Tehama and Shasta Counties, Colorado, in Converse County, Wyoming; and in Chester and Delaware Counties, Pennsylvania, and in 1914, some was washed from chrome sand at Baltimore, Maryland.
202 Descriptive Mineralogy
Metallurgy —The mineral is mined by the usual methods and con- centrated, or, if in large fragments, is crushed It is then fused with certain oxidizing chemicals and the soluble chromates are produced. Or the ore is reduced with carbon yielding an alloy with iron The metal is produced by reduction of its oxide by metallic aluminium or by electrolysis of its salts
jjses — Chromite is the sole source of the metal chromium, which is the chrome-iron alloy employed m the manufacture of special grades of steel Chromium salts are used in tanning and as pigments The crude ore, mixed with coal-tar, kaolin, bauxite, or some other ingredient, is molded into bricks and burned, after which the bricks are used as linings in metallurgical furnaces. These bricks stand rapid changes of temperature and are not attacked by molten metals
Production — The annual production of chromite in the world is now about 100,000 tons, of which Rhodesia produces about J, New Caledonia about and Russia and Turkey about each The produc- tion of the United States in 1912 was 201 tons, valued at $2,753. All came from California. The imports in the same year were 53,929 tons, worth $499,818.
Chrysoberyl
Chrysoberyl is a beryllium alummate, the composition of which is analogous to that of the spinels It may be written Be02(A10)2. Al- though theoretically it should contain 19 8 per cent BeO and 80 2 per cent AkOa, analyses of nearly all specimens show the presence also of iron and magnesium
The mineral differs from spinel in crystallizing in the orthorhombic system (bipyramidal class) Its axial ratio is .4707 : i : 5823 The principal forms observed on crystals are P(in), ooP 06(100), oo P oo (oio), P 06 (on), oo P2(i2o) and 2P?(i2i) (Fig 99) The crystals are often twins (Fig 100), trillings or sixlmgs, with 3? 06 (031) the twinning plane, forming pseudohexagonal groupings (Fig 101) Sim- ple crystals are usually tabular parallel to oo P So (100), which is striated vertically Consequently, in twins this face exhibits stnations arranged feather-like. The angle no A iTo=5o° 21'.
The deavage of chrysoberyl is distinct parallel to Poo (on), and indistinct parallel to oo P 06 (oio) and oo P 56 (100) Its fracture is uneven or conchoidal. Its color is some shade of light green or yellow by reflected light. It is transparent or translucent and in some cases is distinctly red by transmitted light. It is strongly pleochroic m orange,
Aluminates, Ferrites, Etc
green and red tints. The mineral is brittle, has a hardness of 8 5 and a density of about 3 6 Its refractive indices are a=i 7470, j5=i 7484,
Four distinct varieties are recognized
Ordinary, pale green, translucent
Gem, yellow and transparent
Alexandrite, emerald-green in color, but red by transmitted light, transparent, usually in twins Used as a gem
Cat's-eye, a greenish variety exhibiting a play of colors (chatoyancy )
Before the blowpipe the mineral is infusible It yields the Al reac- tion with Co(NOs)2, but otherwise is only slightly affected by the flame It is insoluble in acids
Chrysoberyl is characterized by its crystallization and great hard-
Fig 99
FIG ioo
Fig 101
FIG 99 — Chrysoberyl Crystal with oo P GO 3 100 (a), oo P 55 , oio (b), oo P7, 120 (s),
2&2t 121 P, in (o) and P oo , on (i). FIG 100 — Chrysoberyl Thinned about 3? So (031) FIG 1 01 — Chrysoberyl Pseudohexagonal Sixlmg Twinned about 3? 5 (031)
ness It most closely resembles the beryllium silicate, beryt, in appear- ance, but is easily distinguished from this by its crystallization.
Synthesis. — Crystals have been made by fusing BeO and AkOs with boric acid and then distilling off the boric acid
Occurrence and Origin — Chrysoberyl is found principally in granites and crystalline schists and as grains in the sands produced by the erosion of these rocks In its original position the mineral is a separation from the magma that produced the rocks.
Localities. — Its best known localities are in Minas Geraes, Brazil, near Ekaterinburg, Ural; in the Mourne Mts,, Ireland, at Haddam, Conn , at Greenfield, N. Y.; at Orange Summit, N. Hamp.; and at Norway and Stoneham, Me. The alexandrite comes from Ceylon, where it occurs as pebbles, and from the Urals.
Descriptive Mineralogy
Braunite (MnMnOs) occurs massive and in crystals. The latter are tetragonal (ditetragonal bipyramidal class), 'with a c—i 9922, They are usually simple bipyramids P(in) Because of the nearly equal value of a and c all crystals are isometric in habit The angle iiiAii"i 70° 7' Twins are common, with POO(IOI) the twinning plane Cleavage is perfect parallel to P(III)
The mineral is brownish black to steel-gray m color and in streak Its luster is submetallic Its hardness is 6-6 5 and density 47 It is infusible before the blowpipe With fluxes it gives the usual reactions for manganese It is soluble in HC1 yielding chlorine
It occurs in veins with manganese and other ores in Piedmont, Italy, and at Pajsberg and various other places m Sweden, where its origin is secondary
Hausmannite (MngMnO crystallizes like braumte, but a : i : 1 1573 and its crystals are, therefore, distinctly tetragonal m habit They are usually simply P(ni) or combinations of P(m) and fP(ii3), though much more complicated crystals are known The angle niAi7i=6o° i' Twins and fourlmgs (Fig 102) are common, with
FIG 102 —Hausmannite. (A) Simple Crystal, P, in (p) and oP, ooi (c) (B) Fivelmg Twinned about P oo (101)
P oo (101) the twinning plane The cleavage is imperfect parallel to oP(ooi) The mineral also occurs in granular masses.
Hausmannite is brownish black Its streak is chestnut brown Its hardness is 5-5 5 and density 4 8. Its reactions are the same as those of braumte
Hausmannite occurs as crystals at Ilmenau, Thurmgia, Ilfdd, Harz, and as granular masses in dolomite at Nordmark and several other points in Sweden Like braumte it is probably a decomposition product of other manganese minerals
Chapter X
The Nitrates And Borates The Ottbates
THE nitrates are salts of nitric acid Only two are of importance to us, saltpeter (KNOa) and chile saltpeter (NaNOs) Both are color- less, or white, crystalline bodies, both are soluble m water and both pro- duce a cooling taste when applied to the tongue The potassium com- pound is distinguished from the sodium compound by the flame test Both minerals when heated in the closed tube with KHSOi yield red vapors of nitrogen peroxide (NCfe)
Soda Niter (NaNO3)
Soda niter, or chile saltpeter, is usually m incrustations on mineral surfaces or m massi\ e forms It consists of 63 5 per cent N2Os and 36 5 per cent Na20
Its crystals are in the ditrigonal scalenohedral class of the hexagonal system with an axial ratio of a : c=i : 8297. They are usually rhom- bohedrous R(ioTi) m some cases modified by oR(oooi). Apparently the mineral is completely isomorphous with calcite (CaCOs)
Its cleavage is perfect parallel to the rhombohedron. Its hardness is under 2, its density about 2.27 and its melting point about 312°. Its luster is vitreous, color white, or brown, gray or yellow. The min- eral is transparent Its refractive indices for yellow light are: w 1.5854,
€=13369
Soda niter deflagrates when heated on charcoal and colors the flame yellow. When exposed to the air it attracts moisture and finally lique- fies. It is completely soluble in three times its own weight of water.
Occurrence and Localities — The principal occurrences of the mineral are in the district of Tarapaca, northern Chile, where, mixed with the lodate and other salts of sodium and potassium, under the name caliche, it comprises beds several feet thick on the surface of rain- less pampas, and in Bolivia at Arane under the same conditions. It is associated with gypsum, salt and other soluble minerals. Smaller
206 Descriptive Mineralogy
deposits are found in Humboldt Co , Nevada, m San Bernardino Co , Cal , and in southern New Mexico
The material is thought to result from the action of microorganisms upon organic matter decomposing in the presence of abundant air
Uses —Soda niter is used in the production of nitric acid, and in the manufacture of fertilizers and gunpowder About 480,000 tons are imported into the United States annually at a cost of $15,430,000 Most of it comes from Chile
Since soda niter usually contains sodium lodate as an impurity, the mineral is an important source of iodine.
Niter (KNO3)
Niter, or saltpeter, resembles soda niter in appearance It gener- ally occurs in crusts, in silky tufts and in groups of acicular crystals Its crystals are orthorhombic with a b : 5910 i 7011 Their habit is hexagonal The principal forms observed on them are oo P(i 10), oo P 00(100, oo P 06(010), oP(ooi), P(in), and a series of brachy- domes In many respects the mineral is apparently isomorphous with aragonite which is the orthorhombic dimorph of calcite At 126° it passes over into an hexagonal (trigonal) form Its cleavage is perfect parallel to Poo (on) Its fracture is uneven, its hardness 2 and den- sity 2 i Its medium refractive index for yellow light, /3=i 5056
Niter deflagrates more violently than soda niter and detonates with combustible substances It fuses at aboat 335° It colors the blowpipe flaine violet It is soluble in water
Occurrence and Localities — The mineral forms abundantly in dry soils in Spain, Egypt, Persia, Ceylon and India, where it is produced by a ferment, and on the bottoms of caves m the limestones of Madison Co , Ky , of Tennessee, of the valley of Virginia and of the Mississippi Valley
Production — Most of the niter used in the arts is manufactured, but some is obtained from the deposits m Ceylon and m India The amount imported in 1912 aggregated 6,976,000 Ib , valued at $226,851
The Boraxes
The borates are salts of bone acid, HsBOs, metaboric acid, HBQz, tetrabonc acid, EfeBiOr, hexabonc acid, EUBoOn, and various poly- boric acids in which boron is present in still larger proportion The metaacid is obtained from the orthoacid by heating at 100°, at which
Nitrates And Borates 207
temperature the former loses one molecule of water, thus. H3BO3 — H2O=HBO2, and the tetraacid by heating the ame compound to 160" at which temperature 5 molecules of \\ater are lost from 4 molecules ot the acid, thus 4H3B03-5H2O=H2B407 Hexabonc acid may be regarded as the orthoacid less molecules of water, thus.
Only three of the borates are important enough to be discussed here These are borax, a sodium tetraborate (NaoBOr ioH<zO), cole- manite, a hexaborate (CasBoOn slfeO) and boracite, a magnesium chloro-polyborate (Mg5(MgCl)2Bi6Q3o)- Borax and colemamte are commercial substances that are produced in large quantities
All borates and many other compounds containing boron when pulverized and moistened with HoSO4 impart an intense yellow-green color to the flame If boron compounds are dissolved in hydrochloric acid, the solution will turn turmeric paper reddish brown after drying at 100° The color changes to black when the stain is treated with ammonia.
Borax (H"a2B4O7 roH2O)
Borax occurs as crystals and as a crystalline cement between sand grains around salt lakes, as an incrustation on the surfaces of marshes and on the sands in desert regions, and dissolved in the water of certain lakes in deserts. It occurs also as bedded deposits mterlayered with sedimentary rocks
The composition of borax is 16 2 per cent Na20, 36 6 per cent B2Qs and 47 2 per cent H.
Crystals are monoclmic (prismatic class), with a : b : c=i 0995 : J : -529 and 0=73° 25' FlG I03 —Borax Crystal They are prismatic in habit and in general form with P, no (m), resemble very closely crystals of pyroxene. P5o,iQo The principal planes occurring on them are °IO_(6)' °I°°I !f)' co P 55 (100), oo P(no), oP(ooi), -P(in) and Jj IZI (a) 2p' 221 -2P(22i) (Fig. 103). Their cleavage is perfect parallel to ooP 60(100), and their fracture concfaoidal. The angle noAiTo=93°.
The mineral has a white, grayish or bluish color and a white streak. It is brittle, vitreous, resinous or earthy; is translucent or opaque; has a hardness of 2-2.5, a density of 1.69-1.72, and a sweetish alkaline taste. On exposure to the air the mineral loses water and tends to become white
208 Descriptive Mineralogy
and opaque, whatever its color in the fresh condition Its medium refractive index for yellow light, i 4686
Before the blowpipe borax puffs up and fuses to a transparent globule Fused with fluonte and potassium bisulphate it colors the flame green It is soluble in water, yielding a weakly alkaline solution
Occurrence —The principal method of occurrence of the mineral is as a deposit from salt lakes in and regions, and as incrustations on the surfaces of alkaline marshes overlying buried borax deposits The original beds were deposited by the evaporation to dryness of ancient salt lakes, and the incrustations were produced by the solution of these deposits by ground water, and the nse of the solutions to the surface by capillarity.
Localities.— Borax occurs in the water of salt lakes in Tibet, of several small lakes in Lake County, and of Borax Lake in San Bernardino County in California, and in the mud and marshes around their borders It occurs also in the sands of Death Valley in the same State, and in various marshes in Esmeralda County, Nevada Other large deposits are found in Chile and Peru
Uses — Borax is used as an antiseptic, in medicine, in the arts for soldering brass and welding metals, and in the manufacture of cosmetics Bone acid obtained from borax and colemamte is employed in the manufacture of colored glazes, in making enamels and glass, as an antiseptic and a preservative Some of the borates are used as pig- ments.
Production — Borax was formerly obtained in the United States, especially in California, Oregon and Nevada, by the evaporation of the water of borax lakes, by washing the crystals from the mud on their bottoms and by the leaching of the mineral from marsh soil At pres- ent, however, nearly all the borax of commerce is manufactured from colemanite.
Colemanite (Ca2B6On sH2O)
Colemamte occurs in crystals and in granular and compact masses It is the source of all the borax now manufactured in the United States.
The formula ascribed to the mineral corresponds to 27 2 per cent CaO, 50.9 per cent 6203 and 21 9 per cent H20. As usually found, however, it contains a httle MgO and SiCfe. A crystal from Death Valley, California, yielded:
6203=5070; 0*0=27.31, MgO= 10,
Nitrates And Borates
\1/
The mineral crystallizes in the monoclmic system (prismatic class), m short, prismatic crystals (Fig 104), with the axial constants a:b:c 7769 . i : 5416 and 0=69° 43', The crystals are usual rich in forms Their cleavage is perfect parallel to ocOScloio), and less perfect parallel to oP(ooi) Their fracture is uneven The angle no A 110=72° 4'
Colemanite is colorless, milky white, yellowish white or gray It is transparent or translucent, has a vitreous or adamantine luster, a hardness of 4 to 4 5 and a specific gravity of 2 4 Its index of refrac- tion for yellow light, 18=1.5920
Before the blowpipe it decrep- itates, exfoliates, and partially fuses, at the same time coloring the flame yellowish green. It is soluble in hot HC1, but from the solution upon cooling a volumi- nous mass of boric acid separates as a white gelatinous precipitate
It is easily distinguished from other white translucent minerals, except those containing boron, by the flame test It is distin- guished from borax by its insolu- bility in water and from boracite by its inferior hardness and crystal- lization
Syntheses — Colemanite has been prepared by treating ulexite (NaCaBsOe 8H20) with a saturated solution of NaCl at 70°.
Occurrence and Origin — The mineral occurs as indefinite layers interstratified with shale and limestones that are associated with basalt The rocks contain layers and nodules of colemanite Gypsum is often associated with the borate and m some places is in excess. The cole- manite is believed to be the result of the action of emanations from the basalt upon the limestone.
Localities — Colemanite occurs in Death Valley, California, near Daggett, San Bernardino County, and near Lang Station, Los Angeles County, and at other points in the same State, and in western Nevada, near Death Valley A snow-white, chalky variety (priceite) has been found hi Curry County, Oregon, and a compact nodular variety (pander- mite) at the Sea of Marmora, and at various points in Asia Minor.
Preparation — Colemanite is at the present time the principal source
FIG 104— Colemanite Crystals with =cP no(m), 3? 5, 301 (v), =*P5c, 100 (a), , oro (b); oP, ooi fc), -P, in (£), 2P* 02M), P3b,ouOO, pa, 210 U), aPoo, 201 (A), 2P, 221 (u) and P, In 00
210 Descriptive Mineralogy
of borax The crude material as mined contains from 5 per cent to 35 per cent of anhydrous boric acid (6203) This is crushed and roasted The colemamte breaks into a white powder which is separated from pieces of rock and other impurities by screening, and then is bagged and shipped to the refineries where it is manufactured into borax and boracic acid
Production — The principal mines producing the mineral in 1912 were situated in the Death Valley section of Inyo County, near Lang Station in Los Angeles County, California, and in Ventura County in the same State The total production during the year was 42,315 tons of crude ore, valued at $1,127,813 The imports of crude ore, refined borax and boric acid during the same year were valued at $i 1,200 The production of the United States m boron acid compounds is about half that of the entire world, with Chile producing nearly all the rest
Boracite (Mg5(MgCl)2Bi6O3o)
Boracite is interesting as a mineral, the form and internal structure of which do not correspond, that is, do not possess the same symmetry Its crystals have the well marked hextetrahedral symmetry of the iso- metric system, but their internal structure, as revealed by their optical properties is orthorhombic This is due to the fact that the substance is dimorphous Above 265° it is isometric and below that temperature orthorhombic Crystals formed at temperatures above 265° assume the isometnc shapes. As the temperature falls the substance changes to its orthorhombic form, and there results a pseudomorph of ortho- rhombic boracite after its isometric dimorph
It is a salt of the acid which may be regarded as related to boric acid as follows. SHsBOs— 9H20=H6BsOi5. Ten atoms of hydrogen in two molecules of the acid are replaced by Mgs and the other two by a(MgCl). The resulting combination is 31 4 per cent MgO, 7 9 per cent Cl and 625 per cent BgCioi 8(0-Cl=i 9) The mineral alters slowly, taking up water, so that some specimens yield water on analysis and in the dosed tube (stassfurti e and parasite).
The forms usually found on the crystals are -(in), ooO(no),
ooOoo(icx>),--(iIi) (Fig. 105). Usually the positive and negative
tetrahedrons may be distinguished by their luster, the faces of the posi- tive form being brilliant and those of the negative form dull. The crystals are isolated, or embedded, and rarely in groups They are
Nitrates And Borates 211
strongly pyroelectnc with the analogue pole in the negative tetrahedrons. The mineral is also found massive
Boracite is transparent or translucent and is gra\ , yellow, or green Its streak is white Its luster is vitreous Its cleavage is indistinct parallel to 0(m) and its fracture is conchoidal n The mineral is brittle Its hardness is 7 and its density 3 Its refractive index £, for yellow light, i 667
Boracite fuses easily before the blowpipe with intumescence to a white pearly mass, at the same time colonng the flame green With
copper oxides it colors the flame azure-blue FIG 105 —Boracite When moistened with Co(NOs)2 it gives the Cr>stal with =cO=c, pink reaction for magnesium Some massive /iz;, O, no id), forms yield water in the closed tube, in conse- — , m (0) and — quence of weathering The mineral is soluble , , inHCl ll
Boracite is distinguished from other boron salts by its crystallization, its lack of cleavage and its much greater hardness The massive vari- eties which resemble fine-grained white marble can be distinguished from this by the flame coloration, hardness and reaction with HC1
Syntheses. — Crystals have been formed by heating borax, MgCfe and a little water at 275°, and by fusing borax with a mixture of NaCl and MgCk
Occurrence. — Boracite occurs in beds with anhydrite, gypsum and salt and as crystals in metamorphosed limestones
Localities — It is found as crystals in gypsum and anhydrite at Luneburg, Hanover, and Segeberg, Holstein, in carnallite at Stassfurt, Prussia, and in radiating nodules (stassfurtite) and in massive layers associated with salt beds at the last-named locality It is rare in the United States
Uses and Prodwhon —Boraute is utilized in Europe as a source of boron compounds. Turkey produces annually about 12,000 tons,
Chapter Xi The Carbonates
THE carbonates constitute an important, though not a very large, group of minerals, though one of them, calcite, is among the most com- mon of all minerals They are all salts of carbonic acid (EkCOs) Those in which all the hydrogen has been replaced by metal are normal salts, those in which the replacement has been by a metal and a hydroxyl group are basic salts Both groups are represented by common minerals
The normal salts include both anhydrous salts and salts combined with water of crystallization Illustrations of the three classes of car- bonates are- CaCOs, calcite, normal salt, Na2COs loEfeO, soda, hydrous salt and (Cu OHCOs, malachite, basic salt All carbonates effervesce in hot acids The basic salts yield water at a high tempera- ture only, the hydrous ones at a low temperature
The carbonates are all transparent or translucent, and all are poor conductors of electricity, Most of them are practically nonconductors
Anhydrous Carbonates Normal Carbonates
The anhydrous normal carbonates comprise the most important carbonates that occur as minerals Most of them are included in a single large group whose members are dimorphous, crystallizing in the ditrigonal scalenohedral class of the hexagonal system and in the holo- hedral division (rhombic bipyramidal class) of the orthorhombic sys- tem. The calcium carbonate exists in three forms but only two are known to occur as minerals
Calcite-Aragonite Group
The relation of the dimorphs of this group to one another has been subjected to much study, especially with reference to the two forms of CaCQs- The orthorhombic form, aragonrie, passes into the hexagonal form, calcite, upon heating to about 400°. At all temperatures below 970°, calcite is the stable form Moreover, while calcite crystallizes from a dilute Solution of.CaCQa in water containing 002 at a low tem-
Carbonates 213
perature, aragomte separates at a temperature approaching that of boiling water— the more freely, the less C02 in the solution Arag- omte crystals will also separate from a solution of calcium carbonate, if, at the same time, it contains a gram of an orthorhombic carbonate, or a small quantity of a soluble sulphate Some of the other carbon- ates, for instance, strontiamte (the orthorhombic SrCCfe), pass over into an hexagonal form like that of calcite at 700°, but again change to the orthorhombic form upon cooling For convenience the group is divided for discussion into the calcite division and the aragomte division
Calcite Division
The calcite division of carbonates includes nine or more distinct compounds and a number of well defined \aneties of these Six of the compounds are common minerals Afl crystallize in the ditngonal scalenohedral class of the hexagonal system and are thus isomorphous Their most common crystals have a rhombohedral habit. The names of the six common members with their axial ratios are:
Calcite CaCOs a c=i : 8543
Magnesite MgCOs : 8095
Siderite FeCOs : 8191
Khodochrosite MnCOs .8259
Smit\somte ZnCOs : 8062
There is usually also included in the group the mineral dolomite, which is a calcium magnesium carbonate in which CaCOs and MgCOs are present in the molecular proportions, thus MgCOs CaCOs, or MgCa(COs)2 Its crystals are similar to those of calcite and its physical properties are intermediate between those of calate and magnesite Its symmetry, however, as revealed by etching is tetartohedral (rhom- bohedral class).
The close relationship existing between the members of the group (including dolomite) will be appreciated upon comparing the data in
the following table
Ref Indices
H
Sp
Gr.
a : c
loiiAoiu
tt €
Calcite
3
55'
Dolomite .
o
45'
Magnesite
36'
Sidente
o'
Rhodochrosite
o'
Srmthsonite
20'
8i8±
Descriptive Mineralogy
Calcite (CaCO3)
Calcite is one of the most beautifully crystallized minerals known Its crystals are very common, and sometimes very large They are usually colorless, though sometimes colored, and are nearly always transparent Besides occurring in crystals the mineral is often found massive, in granular aggregates, in stalactites, in pulverulent masses,
Fig 106
Fig 108
Feg. 107 Fig 109
FIG. 106. — Calcite Crystal with — |R, oiTa (e) and R, joTo (m) Nail-head Spar
FIG, 107 — Calcite Crystal with m and e Prismatic Type
FIG 108 — Calcite Ciystals with m, R, 2131 (p) and R, loli (r) Dog-tooth Spar FIG 109 —Calcite with r, v, 4R, 4041 (M) and R8, 3251 (y)
in radial groupings, in fibrous masses and in a variety of other forms As calate is soluble in water containing COa, it has often been found pseu- domorphing other minerals.
Theoretically, calcite contains 56 per cent CaO and 44 per cent COg, but practically the mineral contains also small quantities of Mg, Fe, Mn, Zn and Pb, metals whose carbonates are isomorphous with CaCO&
Hie forms that have been observed on calcite crystals are arranged
Carbonates
in such a manner as to produce three distinct types of habit, as fol- lows (i) the rhombohedral type, bounded by the flat rhombohedrons, R(ioTi), — JR(oiT2) and often blunt scale- nohedrons, like R3(2i3i) and |R2(3i45) in which the rhombohedrons predominate (Fig 106), (2) the pnsmatic type, with the oo P(io7o) predominating, and — £R(oil2) as the principal termination (Fig 107), and (3) dog-tooth spar, contain- ing the same scalenohedrons as on the first type mentioned above with other steeper ones and small steep rhombohedral planes (Fig 108, 109, no) Nail-head spar con- tains the flat rhombohedron — |R(oil2) with the oo P(ioTo) (Fig 106).
Some of the crystals are very compli- cated, belonging to no one of the distinct
types descnbed above, but forming barrel-shaped or almost round bodies Over 300 well established forms have been identified on them.
Twins are common The principal laws are: (i) twinning plane oP(oooi), with the vertical axis common to the twinned parts (Fig 111), (2) twinning plane — fR(oiT2), with the two vertical axes inclined
FIG no— Pnsmatic Crystals of Calcite Terminated by Scalenohedrons and Rhom bohedrons from Cumber- land, England
FIG in.
Fig 112
FIG in — Calate, (2131) Twinned about oP (oooi) FIG 112 — Calcite Twin and Polysynthetic Trilling of R (ion) about — £R (0112)-
at an angle of about 52° (Fig. 112) and (3) twinning plane R(ioTi), with the vertical axes inclined 89° 14' (Fig. 113),
Twins of the second dass can easily be produced artificially on cleav- age rhombs by pressing a dull knife edge on the obtuse rhombohedral edge with sufficient force to move a portion of the mass (Fig. 114). The change of position of a portion of the calcite does not destroy its
Descriptive Mineralogy
transparency in the least Repeated twinning of this kind is frequently seen in marble (Fig 115), there it gives nse to parallel lamellae
The cleavage of calcite is so perfect parallel to R that crystals when
Fig 113 Fig. 114
FIG 113 — Calcite with m, v and e, Twinned about R (loTi) FIG 114 — Artificial Twin of Calcite, with — JR (oils) the Twinning Plane.
shattered by a hammer blow usually break into perfect little rhombo- hedrons Its hardness is about 3 and its density 2 713 Pure calcite is colorless and transparent, but most specimens are white or some pale
shade of red, green, gray, blue, yellow, or even brown or black when very impure, and are translucent or opaque The mineral is very strongly doubly refracting, (see p 213) It is a very poor conductor of electricity.
The principal vaneties of the mineral to which distinct names have been given are:
Iceland spar, the trans- parent variety used in the manufacture of optical instru- ments
Satin spar, a fine, fibrous variety with a satiny luster Limestone, granular ag- occurnng as rock
FIG 115 —Thin Section of Marble Viewed by Polarized Light. The dark bars are poly- synthetic twinning lamellae Magnified 5 diameters.
masses.
Marble, a crystalline limestone, showing when broken the cleavage faces of the individual crystals.
Ltike&apkic stone a very fine and even-grained limestone
Carboxates 217
Stalactites, cylinders or cones of calcite that hang from the roofs of caves They are formed by the evaporation of dripping T\ater
Stalagmites, corresponding cones on the floors of caves beneath the stalactites
Mexican onyx, banded crystalline calcite, often transparent. Usually portions of stalactites
Travertine, a deposit of white or yellow porous calcite produced in springs or rivers, often around organic material like the blades or roots of grass.
Chalk, a fine-grained, pulverulent mass of calcite occurring in large beds
In the closed tube calcite often decrepitates Before the blowpipe it is infusible It colors the flame reddish yellow and after heating reacts alkaline toward moistened litmus paper The mineral dissolves with evolution of CO2 in cold hydrochloric acid Its dissociation tempera- ture l is 898°, though it begins to lose C0> at a much lower temperature
The reaction with HC1, together \vith the alkalinity of the mineral after heating, its softness and its easy cleavage, distinguish calcite from all other minerals In massive forms it has been thought that it could be distinguished from aragomte by heating its ponder with a httle Co(NOs)2 solution Aragomte was thought to become violet-colored in a few minutes while calcite remained unchanged, but recent work proves that this test cannot be relied upon
Syntheses — Calcite crystals are obtained allowing a solution of CaCOs in dilute carbonic acid to evaporate slowly in contact with the air at ordinary temperatures If evaporated at from 80° to 100° ordinary temperatures, or in the presence of a httle sulphate, the ortho- rhombic aragonite will form, Calcite is also formed by heating arag- onite to 400-470°
Occurrence and Origin. — The mineral is widely distributed in beds, in veins and as loose deposits on the bottoms of springs, lakes and nvers. Its principal methods of origin are precipitation from solutions, the weathering of calcareous minerals, and secretion by organisms.
Calcite is the most important of all pseudomorphmg agencies. It forms pseudomorphs after many different minerals and the hard parts of animals
Localities.— The most noted localities of .crystallized calcite are: Andreasberg in the Harz; Freiberg, Schneeberg and other places in Saxony; Kapnik, in Hungary, Traversella, in Piedmont, Alston Moor
1 The dissociation temperature of a carbonate is that temperature at which the pressure of the released CO* equals one atmosphere
218 Descriptive Mineralogy
and Egremont, in Cumberland, Matlock, in Derbyshire, and the mines of Cornwall, England, Guanajuato, Mexico, Lockport, N Y , Ke- weenaw Point, Mich , the zinc regions of Illinois, Wisconsin and Missouri, Nova Scotia, etc
Iceland spar is obtained in the Eskefjord and the Breitifjord in Iceland Travertine is deposited from the waters of the Mammoth Hot Springs, Yellowstone National Park It occurs also along the River Arno, near Tivoli, Rome
Uses. — Calcite has many important uses In the form of Iceland spar, on account of its strong double refraction, it is employed in optical instruments for the production of polarized light Calcite rocks are used as building and ornamental stones They are employed also as fluxes in smelting operations, as one of the ingredients in glass-making and in the manufacture of lime, cement, whiting, and in certain printing operations. Limestone is also used as a fertilizer
Production — The calcite rock marketed in the United States during 1912 was valued at about $44,500,000 It was used as follows In concrete, $5,634,000, in road and railroad making, $12,000,000, as a flux, $10,000,000, as building and monumental stone, $12,800000, in sugar factories, $335,000, as riprap, $1,183,000, for paving, $279,000, and for other uses, $2,400,000 Moreover, the value of the Portland cement manufactured during the year amounted to $67,017,000, the quantity of lime made to $13,970,000, the value of the hydrated lime to $1,830,000, and of sand-lime brick to $1,170,884 The quantity of limestone required for these manufactures is not known, but it was very great.
Magnesite (MgCO3)
Magnesite usually occurs in fine-grained white masses Crystals are rare Pure magnesite consists of 52 4 per cent CCb and 47 6 per cent MgO. It usually, however, contains some iron carbonate
Magnesite is completely isomorphous with calcite Its cleavage is
perfect parallel to R(ioTi). Its hardness is about 4 and the density 3 i.
The mineral is transparent or opaque. It varies in color from white
to brown, but always has a white streak Its dissociation temperature
o
is 445 -
Magnesite behaves like calcite before the blowpipe It effervesces in hot hydrochloric acid and readily yields the reaction for magnesia with Co(NQs)2 It is most easily distinguished from the latter mineral by its density, by the fact that it does not color the blowpipe flame with the yellowish red tint of calcium and does not effervesce in cold HCL
Carbonates 210
Synthesis — Magnesite crystals may be obtained by heating MgSO in a solution of XajCOa at 160° in a closed tube
Occurrence and Origin — Magnesite usual occurs in ems and masses associated with serpentine and other magnesium rocks irom which it has been formed by decomposition It is often accompanied by brucite talc, dolomite and other magnesium compounds It has recently been described as occurring also in a distinct bed near Mohave, CaL, inter- stratified with cla> s and shales It is thought that in this case it ma} have been precipitated fron* solutions of magnesium salts by XaCOs
Localities — The mineral is found abundantly m many foreign local- ities and at Bolton, Mass , Bare Hills, near Baltimore, Md , and in Tulare Co., Cal , and near Texas, Penn The largest deposits are in Greece and Hungary
Uses. — Magnesite is employed very largely in the manufacture of magnesite bricks used for lining converters in steel works, in the lining of kilns, etc , m the manufacture of paper from wood pulp, and in mak- ing artificial marble, tile, etc From it are also manufactured epsom salts, magnesia (the medicinal preparation) and other magnesium com- pounds, and the carbon dioxide used in making soda water
Production — All of the magnesite mined in the United States comes from California, where the yield was 10,512 tons in 1912, valued at $105,120. Most of the magnesite used in the United States is imported from Hungary and Greece In 1912, 14,707 tons of crude material entered the country and 125,000 tons of the calcined product, the total value of which as $1,370,000
Siderite (FeCO3)
Siderite is an important iron ore, though not as much used as formerly It is found crystallized and massive, in botryoidal and globular forms and m earthy masses
In composition the mineral is FeCOa, which is equivalent to 62 i per cent FeO (48 2 per cent Fe) and 37 9 per cent COj- Manganese, calcite and magnesium are also often present in it.
Crystals are more common than those of magnesite. They fre- quently contain the basal plane and the steep rhombohedrons— 8R(o8Si) and — sRfesi). R(ioli) and — |R(oiT2) are common The faces of the rhombohedron are frequently curved. Compare (Fig 125.)
The cleavage of Siderite is like that of the other minerals of this group. Its hardness is 3 5-4 and density 3 85. In color the mineral is sometimes white, but more frequently it is some shade of yellow or brown Its streak is white Most specimens are translucent.
220 Descriptive Mineralogy
In the closed tube siderite decrepitates, blackens and becomes mag- netic It is only slcroly affected by cold acids but it effervesces briskly in hot ones
Siderite is distinguished from the other carbonates by its reaction for iron
The mineral changes on exposure into limonite and sometimes into hematite or even into magnetite
Synthesis — Crystals of sidente may be obtained by heating a solu- tion of FeSCU with an excess of CaCOs at 200°
Occurrence and Origin — The mineral is often found accompanying metallic ores in veins It occurs also as nodules in certain clays and in the coal measures. In some cases it appears to be a direct deposit from solutions In others it is a result of metasomatism and m others is an ordinary weathering product
Localities —The crystallized variety is found at Freiberg, in Saxony, at Harzgerode, in the Harz, at Alston Moor, and in Cornwall, Eng- land, and along the Alps, in Styna and Cannthia Cleavage masses are present in the cryolite from Greenland
Workable beds of the ore are present m Columbia Co , and at Rossie, in St. Lawrence Co , N Y , in the coal regions of Pennsylvania and Ohio, and in clay beds along the Patapsco River, in Maryland The massive or nodular ore from clay banks is known as ironsto? e The impure bedded sidente interstratified with the coal shales is known as black-band ore
Production. — Only 10,346 tons of sidente were produced in the United States during 1912, all of it coming from the bedded deposits in Ohio This was valued at $20,000
Rhodochrosite (MnCO3)
This mineral sometimes occurs in distinct crystals of a rose-red color, but it is usually found in cleavable masses, in a compact form, or as a granular aggregate Sometimes it is m incrustations It is not of commercial importance in North America
Pure manganese carbonate containing 61 7 per cent MnO and 38 3 per cent CQs is rare The mineral is usually impure through the addi- tion of the carbonates of iron, calcium, magnesium or zinc
The most prominent forms on crystals of rhodochrosite are R(ioYi), — |R(oil2), ooP2(ii2o), oR(oooi) and various scalenohedrons
Its cleavage is perfect parallel to R The mineral is brittle Its hardness is about 4 and its density about 3.55 Its luster is vitreous, and its color red, brown, or yellowish gray. Its streak is white When
Carbonates 221
heated it begins to lose CCb at about 320": but its dissociation temper- ature is 632°
The mineral is infusible, but T\hen heated before the blowpipe it decrepitates and changes color When treated in the borax bead it gives the violet color of manganese, and fused with soda on char- coal it yields a bluish green manganate It dissoh es in hot hydro- chloric acid
There are but fe\v minerals resembling pure rhodochrosite m appear- ance From all of these, except the silicate, rhodonite ip 3801, it is distinguished by its reaction for manganese It is distinguished from rhodonite by its hardness, its cleavage and its effervescence with acids The impure varieties are very like some forms of siderite, from which, of course, the manganese test will distinguish it.
Synthesis — Small rhombohedrons of rhodochrosite have been pro- duced by heating a solution of MnSQ* with an excess of CaCCfe at 200° in a closed tube
Occurrence and Origin — Rhodochrosite occurs in veins associated with ores of silver, lead, copper and other manganese ores and in bedded deposits It is the result of hydrothermal or contact metamorphism, and of weathering of other manganese-bearing minerals
Localities. — The mineral is found at Schemmtz, in Hungary, at Nagyag, in Transylvania, at Glendree, County Clare, Ireland, where it forms a bed beneath a bog, at Washington, Conn , in a pulverulent form, at Franklin, N J , at the John Reed Mine, Ahconte, Lake Co , and at Rico, Colo , at Butte City, Mont , at Austin, Xev., and on Placentia Bay, Newfoundland The Colorado and Montana specimens are well crystallized
Uses —The mineral is mined with other ores of manganese. Occa- sionally it is employed as a gem stone.
Smithsonite fZnCO3)
Smithsomte, or "dry-bone ore," is rarely well crystallized. It appears as druses, botryoidal and stalactitic masses, as granular aggre- gates and as a enable earth.
In ZnCOs there are 64 8 per cent ZnO and 35 2 per cent CCte Smith- somte usually contains iron and manganese carbonates, often small quantities of calcium and magnesium carbonates and sometimes traces of cadmium A specimen from Marion, Arkansas, gave:
ZnO CdO FeO CaO CuO CCfe CdS Sift> Total
64 12 .63 .14 .38 tr. 34-68 25 06 100 26
222 Descriptive Mineralogy
The mineral is closely isomorphous with calcite, R(ioTi), — iR(oiT2), 4R(404i), ooR2(ii2o), oR(oooi) and R3(2i3i) being present on many crystals The R faces are rough or curved
Its cleavage is parallel to R(ioli). Its hardness is 5 and its density about 4 4. The luster of the mineral is vitreous, its streak is white and its color white, gray, green or brown It is usually translucent, occa- sionally transparent When heated to 300° for one hour it loses all of its C02
When heated in the closed tube CC>2 is driven off, leaving ZnO as a yellow residue while hot, changing to white on cooling The mineral is infusible before the blowpipe If a small fragment be moistened with cobalt nitrate solution and heated in the oxidizing flame it becomes green on cooling When heated on charcoal a dense white vapor is produced. This forms a yellow coating on the coal, which, when it cools, turns white If this be moistened with cobalt nitrate and reheated in the oxidizing flame it is colored green.
The above reactions for zinc, together with the effervescence of the mineral in hot hydrochloric acid distinguish smithsomte from all other compounds.
Smithsomte forms pseudomorphs after sphalerite and calcite and is pseudomorphed by quartz, hmomte, calamine and goethite
Synthesis — Microscopic crystals of smithsomte may be produced by precipitating a zinc sulphate solution with potassium bicarbonate and allowing the mixture to stand for some time.
Occurrence. — Smithsomte occurs in beds and veins in limestones, where it is associated with galena and sphalente and usually with cala- mine (p 396) It is especially common in the upper, oxidized zone of veins of zinc ores and as a residual deposit covering the surface of weath- ered limestone containing zinc minerals
Localities— The mineral is found at Nerchinsk, Siberia, Bleiberg, in Cannthia; Altenberg, Aachen, Province of Santander, Spain, at Alston Moor and other places in England, at Donegal, in Ireland, at Lancaster, Penn , at Dubuque, Iowa, in Lawrence and Marion Coun- ties, Arkansas; and in the lead districts of Wisconsin and Missouri (see galena and sphalerite).
The Wisconsin and Missouri localities are the most important ones in North America. Here the ore occurs in botryoidal, in stalactitic and in earthy, compact, cavernous masses of a dull yellow color incrusted with druses of smithsonite crystals, of calamine and of other minerals, principally of lead This is the variety known as " dry bone "
Uses — The mineral was formerly an important ore of zinc, being
Carbonates 223
mined alone for smelting It is no\v mined only in connection with calamine and other zinc ores, and all are worked up together. A trans- lucent green or greenish blue variety occurring at Laurium, Greece, and at Kelly, New Mexico, is sometimes employed for ornamental pur- poses. About $650 worth of the material from New Mexico was utilized as gem material in 1912
Aracox1Te Division
This division of the carbonates includes the orthorhombic (rhombic bipyramidal) dimorphs of the members of the calcite group which, together, form a well characterized isodimorphous group. The carbon- ate of calcium is found well crystallized in both dmsions, but the other carbonates are common to one only They actually occur in both divi- sions, but they are found as .common members of one and only as isomorphous mixtures with other more common forms in the other Thus, barium carbonate is a common orthorhombic mineral under the name of uithente It occurs also with CaCOs in mixed crystals under the name bancalcite, or neotype, \*hich is hexagonal. (See also p. 212 and p 213 )
The common members of the aragonite division are:
Aragomte CaCOs Sp Gr. 2 936 a : b : 6228 : i
Stronfaamte SrCOs 706 6090 : i
Witkente BaCOa 325 5949 : i
Cerussite PbCOs ac6 574 6102 : i 7232
Aragonite (CaCOs)
Aragomte occurs m a great variety of forms. Sometimes it is in distinct crystals, but more frequently it is in oolitic globular and reni- form masses, in divergent bundles of fibers or of needle-like forms, in stalactites and in crusts.
In composition aragonite is like calcite. It often contains small quantities of the carbonates of strontium, lead or zinc.
Crystals*are often acicular with steep domes predominating. Some of the simplest crystals consist of oop(uo), ooP 00(010), fP 00(032), Poo (on), 4?(44i), 9P(9Qi) and ooP2(i2o) (Fig. 116). Twinning is common. The twinning plane is often ooP(iio). By repetition this gives nse to pseudohexagonal forms, resembling an hexagonal prism and the basal plane (see Figs 117 and 118), The angle no A i "10=63° 48'.
The cleavage of aragonite is distinct parallel to oo p 06 (oio) and indistinct parallel to oo P(no). Its hardness is 3.5-4 and density about 2 93 Its luster is vitreous and its color white, often tiiigcd with gray,
Descriptive Mineralogy
green or some other light shade Its streak is white and the mineral is transparent or translucent Its indices of refraction for yellow light are a=SI joo, 7=1 6857 At 400° it passes over into calcite
Before the blowpipe aragomte whitens and falls to pieces Other- wise its reactions are like those of caktte, from which it can be distin-
'" ui
Fig 116
Fig 117
FIG 116 — Aragomte Crystal with °o P, no (m), oo P So , oio (6) and P So , on FIG 117 — Aragomtc Twin and Trilling Twinned about co P (no)
A
FIG 1 18— Trilling of Aragomte Twinned about (no) (A) Cross-section (B) Resulting pseudohexagonal group, resembling an hexagonal prism and basal plane
guished by its crystallization, its lack of rhombohedral cleavage and its density
Synthesis —Solutions of CaCOs in dilute HaCOs form crystals of aragomte when evaporated at a temperature of about 90° In general, hot solutions of the carbonate deposit aragomte, while cold solutions deposit calcite If the solution contains some sulphate or traces of strontium or lead carbonates, mixed crystals consisting principally of the aragomte molecule are formed at ordinary temperature,
Occurrence and Origin — Aragomte occurs in beds, usually with gypsurn. It is also deposited from hot waters and from coid waters
Carbonates 225
containing a sulphate (as from sea water) The pearly layer of oyster shells and the body of the shells of some other mollusca are composed of calcium carbonate crystallizing like aragomte Aragomte is often changed by paramorphism into calcite, pseudomorphs of which after the former mineral are quite common
Localities — The mineral is found at Aragon, Spain, at Bilm, in Bohemia, in Sicily, at Alston Moor, England, and at a number of other places in Europe It occurs in groupings of interlacing slender columns (fios /em), m the iron mines of Styria Stalactites are abundant at Leadhills, Lanarkshire, Scotland, and a silky fibrous variety known as satmspar, at Dayton, England
In the United States crystallized aragomte occurs at Mine-la-Motte, Mo , and in the lands of the Creek Nation, Oklahoma Flos fern has been reported from the Organ Mts , New Mexico, and fibrous masses from Hoboken, N J , Lockport, Edenville and other towns in New York and from Warsaw, 111
Strontianite (SrCO3)
In general appearance and in its manner of occurrence strontianite resembles aragomte Its crystals are often acicular in habit though repeated twins are common The angle no A iTo=62° 41'
The composition of pure strontianite is SrO=7o i, C02=2g 9, but the mineral usually contains an admixture of the barium and calcium carbonates
Strontianite is brittle, its hardness is 3 5-4 and its density 3 7
Before the blowpipe strontianite swells and colors the flame with a crimson tinge It dissolves in hydrochloric acid The solution im- parts a crimson color to the blowpipe flame When treated with sul- phuric acid it yields a precipitate of SrSO* Its refractive indices for yellow light are i 5199, 7=1 668 Its dissociation temperature is
"Ss°
Aragomte, witherite (BaCOs) and strontianite are so similar in ap- pearance and in general properties that they can be distinguished from one another best by their chemical characteristics They are all sol- uble in hydrochloric acid and these solutions impart distinctive colors to the blowpipe flame (see p 477)
Syntheses — Crystals of strontianite are obtained by precipitating a hot solution of a strontium salt by ammonium carbonate, and by cool- ing a solution of SrCOs in a molten mixture of NaCl and KC1
Occurrence, — Strontianite occurs in veins in limestone and as an
226 Descriptive Mineralogy
alteration product of the sulphate (celestite) where this is exposed to the weather It is probably in all cases a deposit from water
Localities — Strontiamte is the most common of all strontian com- pounds It frequently occurs as the filling of metallic veins It forms finely developed crystals at the Wilhelmme Mine near Munstei, West- phalia At Schohane, N Y , it occurs as crystals and as gianular masses in nests in limestone It is found also at other places in New York, in Mifflm Co , Penn , and on Mt Bannell near Austin, Texas.
Uses— Strontium compounds are little used m the arts The hydroxide is employed to some extent m refining beet sugar and the nitrate m the manufacture of " red fire " Othei compounds aie used m medicine All the strontium salts used in the United States arc imported
Witherite (BaC03)
Withente differs very little in appearance or in manner of occurrence from aragomte Its crystals are nearly always m repeated twins that
have the habit of hexagonal pyramids (Fig. 119) The angle noAiTo62° 46',
When pure the mineral contains 77 7 pei cent BaO and 22 3 per cent C02
It is much heavier than the calcium car- bonate, its density being 43 Its hardness FIG 119— wuhcriic Twinned is 3 to 4 Its refractive mdc\ foi yellow about COP (no), thus Im.- /s==I740 ils (hbboaation tenii mu- tating Hexagonal Combina- ture Jg 0
It dissolves readily in dilute hydrochloric
acid with effervescence, and from thib solution, even when dilute, sul- phuric acid precipitates a heavy white precipitate of BaSO-t, winch, when heated m the blowpipe flame, imparts to it a yellowish green color
Witherite is distinguished from the other carbonates by its crys- tallization, and the color it imparts to the blowpipe flame.
Syntheses —Crystals are produced by precipitating a hot solution of a barium salt with ammonium carbonate, and by cooling a molten xnagma composed of NaCl and BaCO?
Locahfoes — Witherite is not a very common mineral in the United States, but it occurs in large quantity associated with lead minerals in veins at Alston Moor, in Cumberland and near Hexham, in Northum- berland, England Some of the crystals found in these places measure as much as six inches in length
Carbonates
Its best known locality in the United States is Lexington, Kentucky, where the mineral is associated with the sulphate, bante
Uses — It is used to some extent as a source of banum compounds The importations of the mineral during 1912 aggregate $25,715
Cerussite (PbC03)
Cerussite generally occurs in crystals and in granular, earthy and fibrous masses of a white coloi
The pure lead carbonate contains C02=i6 5 and PbO=835j but the mineral usually contains in addition some ZnCOa
Fig 1 20
Fig 121
Fig 122
FIG 120 — Cerussite Crystal with cop no (w), ooPoo , 100 (0), ooPoo, oio (6), P, in (p), oo P, 130 (r), 2Poo, 021 (i), Pw,on (fc), JPoo, 012 (x) and oP, ooi (c)
FIG 121 — Cerussite Twinned about P(no)
FIG 122 — Cerussite Twinned about
Its simple crystals are tabular combinations of oo P(i 10) , oo P 08 (oio) oo Poo (100) and various brachydomes (Fig 120), and these are often twinned in such a way as to produce six rayed stars (Fig 121), or other symmetrical forms (Fig 122) Groups of interpenetrating crystals are also common The angle iioAiio=620 46'.
The color of the mineral is usually white, but its surface is frequently discolored by dark decomposition products Its luster is adamantine or vitreous and its hardness is 3-3 5 Its density =6.5 Its refractive indices for yellow light are a i 8037, £ 2 0763, 7=2 0780
The mineral is dissolved by nitric acid with effervescence and by potassium hydroxide Before the blowpipe it decrepitates, turns yellow and changes to lead oxide On charcoal it is reduced to a metallic globule, and yields a white and yellow coating
228 Descriptive Mineralogy
Cerussite is not easily confused with other minerals It is well char- acterized by its high specific gravity, its reaction for lead, and is dis- tinguished from the sulphate (anglesite) by effervescence with hot acids
Syntheses —Crystals have been obtained by heating lead formate with water in a closed tube, and by treatment of a lead salt by a solution of ammonium carbonate at a temperature of iso°-i8o°
Occurrence and Origin — The mineral occurs at all localities at which other lead compounds are found, since it is often produced from thes*
FIG 123 — Radiate Groups of Cerussite on Galena from Park City Distrid, Utah. (After J M BoHlwell)
latter by the action of the atmosphere and atmospheric water It is, therefore, usually found m the upper portions of veins
Locates —Cerussite crystals of great beauty are found m many of the lead-producing districts of Europe and also at Phoemxville, Penn ; near Union Bridge, m Maryland, at Austin's Mines, Wythe Co., Vir- ginia, and occasionally in the lead mines of Wisconsin and Missouri, In the West it occurs at Leadville, Colo , at the Flagstaff and other mines m Utah (Fig 123), and at several different mines in Arizona.
Uses, — It is mined with other lead compounds as an ore of the metal
Carbonates 229
Dolomite (MgCa(CO3)2)
Dolomite is apparently isomorphous with calcite but the etch figures on rhombohedral -faces prove it to belong m the trigonal rhombohedral class It occurs as crystals and in all the forms charac- teristic of calcite except the fibrous
Nearly all calcite contains more or less magnesium carbonate, but most of the mixtures are isomorphous with calcite and magnesite When the ratio between the two carbonates reaches 5435 per cent CaCOs 45 65 per cent MgCOs, which is equal to the ratio between the molecular weights of the two substances, or in other words when the two carbonates are present in the compound in the ratio of one molecule to one molecule, the mineral is called dolomite The calculated com- position of dolomite (MgCa(COs)2) is 30 4 per cent CaO, 217 per cent MgO and 47 8 per cent CCte
The crystals of dolomite are usually rhombohedral combinations of the rhombohedron R(ioli) with the scalenohedron R3(2i3i) (Fig 124), and its tetartohedral forms, and often the prism oop2(ii2o) and the basal plane Its axial ratio is a:c**im 8322 Twins are not rare, with oR(oooi) and R(ioTi) the twinning planes The R planes are often curved, frequently with concave surfaces (Fig 125) The
angle loli A7ioi 730. ,
rro. i i j i -j. -£ i. ni FIG 124— Dolomite
The cleavage of dolomite is perfect parallel crystal with 4R
to R The mineral is brittle Its hardness is 40T and Op' 3 5-4 and density 2 915 Its luster is vitreous or oooi (c) pearly and its color white, red, green, gray or brown Its streak is always white and the mineral is translucent or transparent Its refractive indices for yellow light are 16817, i 5026 The important varieties recognized are Pearlspar, with curved faces having a pearly luster Granular or saccharoidd, including many marbles and magne'San limestones
Dolomifoc limestone, including much hydraulic limestone Many dolomites are intermixed with the carbonates of iron, manga- nese, cobalt or zinc and these are known as ferriferous dolomite, etc
Dolomite behaves like calcite before the blowpipe and in the closed tube It, however, dissolves only slowly, if at all, m cold hydrochloric acid, except when very finely powdered, though dissolving readily with effervescence in hot acid
230 Descriptive Mineralogy
The reaction toward cold acid and its greater hardness easily dis- tinguish dolomite from calcite It is distinguished from magnetite by the flame reaction
Occurrence and Origin —Dolomite, like the calcium carbonate, occurs crystallized m veins, and as granular masses forming gicat beds of rock It is a precipitate from solutions and a metasomatic alteration product of calcite
Localities — Its crystals are present at many places, among them Bex, in Switzerland, Traversella, in Piedmont, Guanajuato, in Mexico, Roxbury, in Vermont, Hoboken, N J., Niagara Palls, the Quarantine
FIG 125. — Group of Dolomite Crystals from Jophn, Mo Flat Rhombohedrons with
Curved Faces
Station, and Putnam, N. Y , Joplin, Mo , and Stony Pouil, N C. It is also very widely spread as beds of dolomitic limestone
Uses — Dolomite is used for many of the purposes served by calcite, indeed, much of the material used as marble, limestone, etc , contains a large percentage of magnesium carbonate It is not, however, used as a flux or m the manufacture of Portland cement, nor as a source of lime
Ankerite (Ca(Mg Fe) (003)2) is a ferruginous dolomite. It is an isomorphous mixture of the carbonates of calcium, magnesium and iron, in which the FeCOa replaces a part of the MgCOs in dolomite It is usually in rhombohedral crystals, with the angle xoTi A 1101-73° 48' Its color is white, gray or red and its streak is white Its hardness 5-4, and its density 2 98 It also occurs m coarse and fine-grained granular masses, Ankente is infusible before the blowpipe. In the
Carbonates 231
closed tube it darkens and when heated on charcoal it becomes mag- netic It occurs in veins, especially those containing iron minerals It has been found at Antwerp and other places m northern New York.
Calcium-Barium Carbonates
Carbonates of the general composition CaBa(COs)2 occur (i) as a series of mixed crystals isomorphous with caicite under the name hart- calctte, (2) as a series of mixed crystals isomorphous with aragomte known as alstomte or bromate, and (3) a typical double salt, barytocalctte, which is monoclmic Both alstomte and barytocaicite occur in veins of lead ores and of bante
Barytocaicite, CaBa(COs)2 is monoclmic (prismatic class), with a : b . 7717 i 6255 and £=73° 52' It forms crystals bounded by oo P 66 (100), ccP(no), oP(ooi), and a series of clmopyramids, of which 2P2 (12!) and sP$ (i 5!) are common It also occurs massive Its perfect cleavage is parallel to ooP(no) The mineral is white, gray, greenish or yellowish Its streak is white, hardness and sp gr 3 665 It is transparent or translucent Before the blowpipe frag- ments fuse on thin edges, and assume a pale green color, due to the presence of a little manganese The mineral is soluble in HC1 Its principal occurrence is Alston Moor, Cumberland, England.
Basic Carbonates
The basic carbonates are salts in which all or a portion of the hydro- gen of carbonic acid is replaced by the hydroxides of metals There are only three minerals belonging to the group that need be referred to here Two are copper compounds One is the bright green malachite and the other the blue azunte The composition of the former may be
CuOHv
represented by the formula ;>C03, and that of the latter by
CuOH/
CuOHv
Cu==(COs)2. Both are used to some extent as ores of the metal, CuOH/
though their value for this purpose is not great at the present time They may easily be distinguished from all other minerals by their distinctive colors, by the fact that they yield water in the closed tube and by their effervescence with acids The third mineral (hydrozincite) is a white substance that occurs as earthy or fibrous incrustations on other zinc compounds. Its composition corresponds to 2ZnCOs sZn(OH)2
232 Descriptive Mineralogy
Its hardness 2-2 5 and its specific gravity is about 3 7 Only the two copper compounds are described m detail
Malachite ((CuOH)2CO3)
Malachite usually occurs in fibrous, radiate, stalactitic, granular or earthy, green masses, or as small drusy crystals covering other copper compounds The mineral contains, when pure, 19 9 per cent CO2, 71 9 per cent CuO and 8 2 per cent KbO
Well defined crystals are usually very small monoclmic prisms (mon- oclmic prismatic class), with an a\ial ratio 8809 i 4012 and #=6i° 50' Their predominant forms are ooPoo(ioo), ooPo>(oio), ooP(no), and oP(ooi) Contact twins arc common, with oo P 60(100) the twinning plane (Fig 126) The angle no A iTo= 75° 40'
The puie mineral is bright green in color and has a light green stieak It possesses a vitieous luster, FIG 126 -Malachite but this becomes silky m fibrous marc* and dull Crystal with m massive specimens Crystals are translucent no (w), ooPw, and massive pieces aic opaque. Translucent ioo (a), and oP, pieces are pleochroic in yellowish green and dark cot (c) Twinned green Thc clcavage 1S perfect paidud to
oP(ooi) Thc haidness of malachite is 3 5-4, and its density about 3 9 Its refractive index, /3, for yellow light 88
Malachite turns black and fuses befoic the blowpipe and tinges the flame green With NaaCOs on charcoal it yields a copper globule. It is difficultly soluble m pure water, but is easily dissolved m water con- taining C02 It is soluble with effervescence in HCl and its solution becomes deep blue on the addition of an excess of ammonia. When heated in a closed glass tube, it gives an abundance of water. Boiled with water it turns black and loses its COa
Malachite, on account of its characteristic color, may be easily dis- tinguished from all other minerals but some varieties of turquoise and a few copper compounds, such as atacamite (p 144) It may be dis- tinguished from all of these by its effervescence with acids
Synthesis. — Malachite crystals have been obtained with the form of natural crystals by heating a solution of copper carbonate m ammonium carbonate
Occurrence and Origin — Malachite is a frequent decomposition product of other copper minerals, being formed rapidly in moist places.
Carbonates 233
It occurs abundantly in the upper oxidized portions of veins of copper ore, where it is associated with azurite, cuprite, copper, kmomte and the sulphides of iron and copper, often pseudomorphmg the copper minerals The green stain noticed on exposed copper trimmings of buildings is composed in part of this substance
Localities — The mineral occurs in all copper mines At Chessy, France, it forms handsome pseudomorphs after cuprite In the United States it has been found in good specimens at Cornwall, Lebanon Co , Penn , at Mineral Point, Wisconsin, at the Copper Queen Mine, Bisbee, and at the Humming Bird Mine, Morenci, Arizona, and in the Tintic district, Utah.
Uses —In addition to its use as an ore of copper the radial and mass- ive forms of malachite are employed as ornamental stones for inside decoration The massive forms are also sawn into slabs and polished for use as table tops and are turned into vases, etc
Production — As malachite is mined with other copper compounds, the quantity utilized as an ore of the metal is not known The amount produced in the United States during 1912 for ornamental purposes was valued at $1,085 This, however, included also a mixture of malachite and azurite.
Azurite (Cu(CuOH)2(CO3)3)
Azurite is more often found in crystals" than is malachite. It occurs also as veins and incrustations and in massive, radiated, and earthy
FIG 127— Azurite Crystals with oP, oot (c), -Pco, 101 (<r), ooPoo, 100 (a), P, YII oo P, no -2P, 221 (A), jPa, 243 (d) and P & , on (/)
forms associated with malachite and other copper compounds. Its most frequent associate is malachite, into which it readily alters
In composition azurite is 25 6 per cent CCh, 69 2 per cent CuO, and 5 2 per cent EfeO It changes rapidly to malachite, and sometimes is reduced to copper
The crystals are tabular, prismatic, or wedge-shaped monochmc forms (monochmc prismatic dass), with an axial ratio a . b : 8501 : i : r 7611, and P~Bj° 36', They are usually highly modified, 58 or
234 Descriptive Mineralogy
more different planes having been identified on them The predominant ones are oP(ooi), — POO(IOI), ooP(no), -2P(22i) and oopoo(ioo). (Fig 127 ) The angle no A 1*0=80° 40'
The mineral is dark blue, vitreous, and translucent or transparent, and is pleochroic in shades of blue It is brittle Its streak is light blue, its hardness 3 5-4 and density 3 8 Its cleavage is distinct parallel to Poo (on)
The blowpipe and chemical reactions for azunte are the same as those for malachite By them the mineral is easily distinguished from the few other blue minerals known
Synthesis — Crystals have been formed on calcile by allowing frag- ments of this mineral to lie in a solution of CuNOj for a year or more
Occurrence — The mineral occurs in the oxidized zone of copper veins. It is an intermediate product m the change of other coppei compounds to malachite
Localities — Azunte occurs m beautiful crystals at Cressy, France, near Redruth, in Cornwall, at Phoenix ville, , at Mineral Point, Wis , at the Copper Queen Mine, Bisbce, Aiu , at the Mammoth Mine, Tintic district, Utah, at Hughes's Mine, California, and at many other copper mines in this country and abroad
From Morenci, Ariz , Mr Kunz describes specimens consisting of spherical masses composed of alternating layers of malachite and azunte, which, when cut across, yield surfaces banded by alternations of bright and dark blue colors
Uses — Azurite is mined with other copper minerals as an ore of cop- per It is also used to a slight extent as an ornamental stone (see mal- achite).
Hydrous Carbonates
The hydrous carbonates are salts containing water of crystalliza- tion They are carbonates of sodium or of this metal with calcium or magnesium Some of them occur in abundance in the waters of salt or bitter lakes, but very few are known to occur m any large quantity in solid form Among the commonest are:
Soda or natron Na2COa xoBfeO monochmc
Trona HNas (C0s)2 - aEfeO monoclmic
Gayliissite NagCa(C03)2 sEfeO monoclimc
Hydromagnestie MgOHCOaVsBfeO orthorhombic
These minerals occur either m the muds of lakes or as crusts upon the mud or upon other minerals,
Carbonates 235
Natron occurs only in solution and in the dry mud on the borders of lakes
Trona, or urao, (HNa3(C03)2 2H20) is found as crystals in the mud of Borax Lake, California, as a massive bed in Churchill Co., Nevada, and as thin coatings on rocks in other places. Its crystallization is monochnic (pns- c matic class), with the axial ratio, 2 8426 : i . V 7
29494 and 18=76° 31' Its crystals are usually
bounded by oP(ooi), ooP 66(100), -P(m) and FIG 128— Trona Ciys- +P(Tn) (Fig 128) Fibrous and massive forms tal with oP, ooi (c), are common The mineral has a perfect cleavage °° p I0° (fl) and paraUel to oo P 60 (100) It is gray or yellowish +P' m (o) and has a colorless streak It has a vitreous luster, a hardness of 2 5-3, and a density of 2 14 It is soluble in water and has an alkaline taste It exhibits the usual reactions for Na and for carbonates
Gaylussite (Na2Ca(COs)2 5H20) also occurs as crystals in the muds of certain lakes, especially Soda Lake, near Ragtown, Nevada, and Menda Lake, Venezuela, and in clays under swamps in Railroad Valley, in Nevada Its crystals are monochnic (prismatic class) with a : b : c=i 4897 : i : 1 4442 and 0=78° 27' They are usually bounded by oo P(no), P oo (on), and P(Ti2) (Fig 129), or by these planes and oP(ooi) and oo P 66 (100). They are either prismatic because of the predominance of Pob(oii) and oP(ooi), or are octahedral m habit because of the nearly equal development of P ob (on) and oo P(iio). Their cleavage is perfect FIG 1 29 -Gaylussite para]iel to ooP(no)
no (m), Poo ,011 J
(e)and JP,Ti2 (r). lucent Its hardness is 2-3 and density 199
It is very brittle When heated m the closed
tube it decrepitates and becomes opaque It loses its water at 100°
In the flame it melts easily to a white enamel and colors the flame yellow
It is partially soluble in water, leaving a white powdery residue of CaCOs
and is entirely soluble in acids with effervescence The mineral occurs
in such large quantity in the clays underlying swamps in Railroad Valley,
Nevada, that its use has been suggested as a source of NagCOs-
Chapter Xii The Sulphates
THE sulphates are salts of sulphuric acid A large number are known to occur in nature but many of them are dissolved in the waters of salt lakes Of the remaining ones only a few are very common These may be divided into an anhydrous normal group, a basic group and a hydrated group In addition, there are several minerals that are sulphates mixed with chlorides or carbonates
All the sulphates that are soluble in water give the test for sulphuric acid When heated with soda on charcoal they are reduced to sulphides The mass when placed on a silver com and moistened with a drop of water or of hydrochloric acid partly dissolves and stains the silver dark brown or black
The sulphates when pure are all white and transparent, and are all nonconductors of electricity
Anhydrous Sulphates Normal Sulphates
The anhydrous normal sulphates ha\c the general formula R/2S04 or R"S04 The most common ones are sulphates of the alkaline earths and lead They belong in a single group which is orthorhombic The few less common ones are sulphates of the alkalies or of the alkalies and alkaline earths Only two of the latter are described*
Glauberite (Na2Ca(SO4)2)
Glaubente may be regarded as a double salt of the composition NaaS04 CaSO/t, which requires 511 per cent Na2S04 and 48.9 per cent CaS04 The mineral contains 22 3 per cent Na20, 20 i per cent CaO and 57 6 per cent SOs
It nearly always occurs in monochmc crystals (prismatic class), with an axial ratio i 2209 . i i 0270 and #=67° 49'. The most fre- quent combination is oP(ooi), — P(ni), ooP(no), ooP 06(100), 3P3(3iT) and +P(u7), with oP(ooi) prominent (Fig 130) The cleavage is perfect parallel to oP(ooi) The angle noAiTos=96° 58'.
Sulphates
Glaubente is yellow, gray or brick-red m color, is transparent or translucent and has a white streak, a vitreous luster and a conchoidal fracture Its hardness is 2 5-3 and its specific gravity about 28 It is brittle It is partly soluble m water, imparting to the solution a slight saltiness The red color of many speci- mens is due to the presence of inclusions
Before the blowpipe the mineral decrepi- tates, whitens and fuses easily to a white enamel, at the same time coloring the flame FIG 130— Glaubente Crys- yellow It is soluble m HC1 and in a large talwithoP.ooi quantity of water In a small quantity of water it is partially dissolved with loss of transparency and the production of a deposit of
It sometimes alters to calcite
Occurrence— Glaubente is associated with rock salt and other de- posits from bodies of salt water It is found at Villa Rubia, m Spam, and elsewhere in Europe, and m the Rio Verde Valley, Arizona and at Borax Lake, California
no (m), oo P oo , 100 (a) and — P, in (s)
FIG 131 — Thenarditc Crystal with oo P, no (w), P, nT (o), IPS, 106 (0 and oP, ooi (c)
Thenardite (Na2S04) occurs as ortho- rhombic crystals in the vicinity of salt lakes, and m beds associated with other lake deposits Its crystals ha\e an axial ratio 5976: i i 2524 They are commonly prismatic but those from California are tabular and are bounded by ooP(uo), oP(ooi), P(iiT), £P 60(106), and ooPw(ioo) (Fig 131) Twins are common (Fig 132)
The mineral is colorless, white or reddish and has a salty taste Its hardness is 2-3 and Its specific gravity 2 68 Its inter- mediate refractive index is i 470 It is readily soluble in water. It occurs in exten- sive deposits in the Rio Verde Valley, Ari- zona, and as crystals at Borax Lake, Cali- fornia and on the shores of salt lakes in Central Asia and South America.
FIG 132 —Thenardite Twinned about P 06 (on) Forms same as m Fig. 131 and oo P oo , 100 (a)
238 Descriptive Mineralogy
Barite Group
The bante group includes the sulphates of the alkaline earths and lead They are all light colored minerals with a nonmetallic luster They all crystallize in the orthorhombic system (bipyramidal class), and all have a hardness of about 4 The minerals comprising this group, with their axial ratios, are
Anhydnte CaSO* a b : 8932 ' i i 0008 Bante BaS04 =8152 i 1 3136
Celestite SrS(>4 7790 i . i 2800
Angleute PbSQi 7852 : i . i 2894
Anhydrite (CaSO4)
Calcium sulphate is dimorphous The natural compound, anhy- drite, is orthorhombic bipyramidal In addition to this, there is another which passes over into anhydrite when shaken for a long time with boiling water It is produced by dehydrating gypsum at about 100° When moistened it combines with water and passes back to gypsum It is probably tnclmic It is unstable under the conditions prevailing at the earth's suiface and is, therefore, not found as a mineral
Anhydrite occurs usually m fibrous, granular or massive forms, not often in crystals When crystals occur they are commonly prismatic or tabular m habit
In composition the mineral is 58 8 per cent SOa and 41 2 per cent CaO
Its crystals are usually bounded by the three pinacoids oP(ooi), oo P 60(100), oo p 06(010) and P(ni), 2P2(i2i), 3P3(i3i), POO(IOI) and Poo (on) The prismatic types are usually elongated parallel to the macroaxis The angle noAiTo=83° 41'
Anhydrite fuses quite easily before the blowpipe and colors the flame reddish yellow It is very slightly soluble in water but is completely dissolved in strong sulphuric acid It cleaves parallel to the three pm- acoids yielding rectangular fragments. Its hardness is 3-3 5 and den- sity about 2 93 Its luster is vitreous m massive pieces and its color white, often with a distinct tinge of blue, gray or red. In small frag- ments it is translucent, but in large masses it is opaque Its refractive indices for yellow light are i 5693, 7=1 6130
It is distinguished from the other sulphates by its specific gravity and the color it imparts to the blowpipe flame
Sulphates 239
Synthesis — Its crystals have been produced by slowly evaporating a solution of gypsum in HfoSCX
Occurrence — Anhydrite occurs as crystals implanted on the minerals of ore veins, cis beds of granular masses associated with gypsum, and as crystalline masses in layers associated with rock salt — the two having been deposited by the evaporation of salt waters
Localities — The mineral is found at the salt mines of Stassfurt, in Germany, Hail, in Tyrol, Bex, in Switzerland, in the ore veins of Andreasberg, m Harz, Bleiberg, m Carmthia, and at many other places m Europe At Lockport, N Y , and at Nashville, Tenn , it occurs as crystals lining geodes m limestone, and at the mouths of the Avon and St Croix Rivers m Nova Scotia it forms large beds associated with gypsum
Uses — Finely granular forms of the mineral are used for ornamental purposes, and as a medium for the use of sculptors The massive variety is occasionally employed as a land plaster to enrich cultivated soils
Barite (BaSO4)
Bante, or heavy spar, usually occurs crystallized, though it is also often found massive and in granular, fibrous and lamellar forms It is a common mineral associated with sulphide ores as a gangue
The mineral is sometimes pure but it is usually intermixed with the isomorphous calcium and strontium sulphates The pure mineral con- tains 34 3 pei cent SOs and 65 7 per cent BaO As usually mined it contains SiOa, CaO, MgO, AlgOa, FegOa and in some instances PbS2 (galena)
The simple crystals are usually tabular or prismatic in habit. The tabular forms are commonly bounded by oP(ooi), ooP(no) and the domes, P 66 (101), ob (102), 2P 06 (021), and P 06 (on), and sometimes P(ni) and oo Poo (100) (Fig. 133), The prismatic forms are usually elongated m the direction of the a axis, and are bounded by the same planes as the tabular crystals (Fig 134) FlG I33 —Bante Crystals with oop, J10 (m), Complex crystals are also iPoo, 102 (d), PoS,oii (0) and oP, ooi (c) abundant They are often
beautifully supplied with planes, the total number known on the species being about 100 The angle noAiioT80 22?'
The cleavage of bante is perfect parallel to oP(ooi) and oo P(no) It is brittle Its hardness is about 3 and its density about 4 5 The
240 Descriptive Mineralogy
mineral is white, often with a tinge of yellow, biown, blue, 01 red It is transparent or opaque and its streak is white Its refi active indices for yellow light die i 6369, i 6491
Before the blowpipe bante decrepitates and fuses, at the same time
coloring the flame yel- lowish green The fused mass reacts alkaline to
lltmus paper Jt 1S m"
The mineral barite is FIG 134 -Bante Crystals with m, d, o and c as m distinguished from the Fig 133 Also coPoo, zoo (a), P, m 60 and
P2, 122 (y) l /
high specihc gravity and
the color it imparts to the blowpipe flame
Syntheses — Crystals have been made by heating precipitated barium sulphate with dilute HC1 in a closed tube at 150°, and by cooling a fusion of the sulphate in the chlorides of the alkalies or alkaline earths
Occurrence and Origin — Bante is a common vein-stone It con- stitutes the gangue of many ore veins, particularly those of copper, lead and silver. It is found also as a replacement of limestone, which, when it weathers, leaves the barite in the form of fragments and noduleb in a residual clay, and as a deposit in hot . In all cases it is believed to be a deposit from solutions
Localities —Barite occurs abundantly in England, Scotland, and on the continent of Europe Crystals are found at Cheshire, Conn ; at DeKalb, St Lawrence Co , N Y , at the Phoenix Mine in Cabarrus Co,, N C , and near Fort Wallace, New Mexico Massive barite m pieces large enough to warrant polishing is found on the bank of Lake Ontario, at Sacketts Harbor, N Y It constitutes the filling of veins at many different places, more particularly in the southern Appa- lachians and m the Lake Superior region,
Preparation — Much of the mineral that enters the trade in the United States is obtained from the deposits in residual clay The rough material is washed, hand picked, crushed, ground and treated with sulphuric acid. The acid dissolves most of the impurities and leaves the powdered mineral white
Uses —The white varieties of the mineral are ground and the powder is used in making paints The mineral is also employed in the manu- facture of paper, oilcloth, enameled ware, and m the manufacture of barium salts, the most important of which is the hydroxide, which is employed m refining sugar.
Sulphates 241
The colored massive varieties, more especially stalactitic and fibrous forms, are sawn into slabs, polished and used as ornamental stones
Production— The quantity of bante mined in the United States during 1912 was over 37,000 tons, valued at $153,000 The principal producing states are Missouri, Tennessee and Virginia. The imports in the same year were about 26,000 tons of crude material, valued at $52,467 and 3,679 tons of manufactured material, valued at $26,848 Besides, there were imported $70,300 worth of artificial barium sul- phate and about $280,000 worth of other barium salts, exclusive of witherite.
Celestite (SrSO*)
Celestite occurs in tabular prismatic crystals, in fibrous and some- times in globular masses Though usually white, it often possesses a bluish tinge, to which it owes its name
The theoretical composition of the mineral is 43 6 per cent 80s and 56 4 per cent SrO, but it often contains small quantities of the isomorphous Ca and Ba compounds
Many celestite crystals are very similar in habit to those of bante.
FIG. 135 —Celestite Crystals with oo p, no (w), iPoo, 102 (<Q, J Poo, 104 (r), oo P oo , oio (&), P oo , on (0) and oP, ooi (c)
Tabular forms are perhaps more common (Figs. 135), Occasionally, pyramidal crystals are bounded by PiJ(i44), °oP(ioo), Poo (on) and oP(ooi) These often have rounded edges and curved faces and thus come to have a lenticular shape. The angle no A iTo= 75° 50'
The cleavage of the mineral is perfect parallel to oP(ooi) and almost perfect parallel to oo P(IIO) Its hardness is about 3 and its specific gravity 3 95. Its luster and streak are like those of barite. Its color is often pale blue and sometimes light red, but pure specimens are white or colorless. Its refractive indices for yellow light are: i 6220, 7=1 6237
Before the blowpipe celestite reacts like barite except that it tinges the flame crimson This crimson color may be obtained more dis- tinctly by fusing a little powder of the mineral on charcoal in the reduc-
242 Descriptive Mineralogy
mg flame and dissolving the resulting mass in a small quantity of hydro- chloric acid, then adding some alcohol and igniting the mixture
Syntheses — Crystals of celestite are produced in ways analogous to those in which bante crystals are formed
Occurrence and Ongin —Celestite occurs in beds with rock salt and gypsum, as at Bex, Switzerland, associated with sulphur, as at Gir- genti, Italy, and in crystals and grams scattered through limestone, as at Strontian Island, Lake Erie, and in Mineral Co , W Va , or as crystals lining geodes in the same rock It is also sometimes found as a gangue in mineral veins In some instances it was deposited by hot waters, in others by cold waters, and in others it was concentrated by the leaching of strontium-bearing limestones by atmospheric water
Production and Uses — Although the mineral occurs in large quan- tity at a number of places in the United States and Canada it is not mined A small quantity of the strontium oxide is annually imported Strontium salts, prepared from celestite in part, aie used in the manu- facture of fireworks and medicines and m refining sugar.
Anglesite (PbSOt)
Anglesite occurs principally as crystals associated with galena and other ores of lead, but is found also massne, and in granular, stalactitic and nodular forms
The theoietical composition of the mineral demands 73 6 per cent PbO and 26 4 S03
Its orthorhombic crystals are usually prismatic or isomctnc in habit Tabular habits are less common than in bante and celestite The principal forms occurring are ooPcfc (100), <*>P(iio), iPoo (102), and other macrodomes, P oo (on) and various small pyramids, with oP(ooi), m addition, on the tabular crystals (Figs ij6, 137, 138), The angle no A iTo=76° i6J'
The cleavage of anglesite is distinct parallel to oP(ooi) and oo P(i 10) Its fracture is conchoidal The mineral is white, gray or colorless and transparent, and is often tarnished with a gray coating. It has an adamantine or residuous luster, is bnttle and has a colorless streak Its hardness is 2 5-3 and sp gr 6 3-6 4. Impure varieties may be tinged with yellow, green or blue shades and m some cases may be opaque Its refractive indices for yellow light are i 8771, 7 i 8937.
Before the blowpipe anglesite decrepitates It fuses m the flame of a candle On charcoal it effervesces when heated with the reducing flame and yields a button of metallic lead In the oxidizing flame it
Sulphates
gives the lead sublimate The mineral dissolves m HN03 with dif- ficulty
The mineral is characterized by its high specific gravity and the
Fig 136 Fig 137
FIG 136 — Ynglesilc Crystal with w P, no (m), ooPw, 100 (a), oP, ooi (c),
JP, 112 (/) and Pi, 122 (y)
FIG 137 — \nglcsitc Crystal with /;/, a and y as in Fig 136 Also oopoo, cio (bj, P oo , on (o), P, in (s) and JP oo , 102 (d)
reaction for lead. It is distinguished from (.erussrte by the reaction for sulphur and the lack of effervescence with HC1
Syntheses — Crystals of anglesite have been made by methods anal- ogous to those used in the preparation of bante crystals
Occurrence — The mineral occurs as an alteration product of galena,
mainly in the upper portions of veins of
lead ores Under the influence of solu- tions of carbonates it changes to cerus- site
Localities —It is found in Derby- shire and Cumberland, in England, near Siegen, in Prussia, m Australia and in the Sierra Mojada, m Mexico In the United States crystals occur at Phoenix-
ville, Penn , in the lead districts of the Mississippi Valley, and at various points in the Rocky Mountains
Use*. — It is mined with other lead compounds as an ore of this metal
Basic Sulphates
Although several basic sulphates are known as minerals, only two are of importance One, brochantite, is a copper compound found, with other copper minerals, in the oxidized portions of ore veins, and the other, alumte, is a double salt of aluminium and potassium. This min-
FIG 138 —Anglesite Crystal with m, y, c and d as in Figs 136 and 137 Also iP 63 , 104 (Q and P?, 144 (x)
244 Descriptive Mineralogy
eral is one of a series of compounds forming an isomorphous group, with the general formula (R'"(OH)2)6R'2(S04)4 or (R'''(OH)2)oR''(SOi)i, in which R'"=A1 or Fe, R'2=K2, Na2 or H2 and R"=Pb
Alumte ((A1(OH)2)6K2(S04)4)
Alunite, or aiumstone, is a comparatively rare mineral, but, because of its possible utilization as a source of potash, it is of considerable in- terest It has long been used abroad as a source of potash alum
The mineral, when pure, contains 38 6 per cent 863, 37 o per cent Al20s, ii 4 per cent K20 and 13 o per cent EkO, which corresponds to the formula given above, or if written in the form of a double salt 3(A1(OH)2)2S04 K2S04 The chemical composition of a crystalline specimen from Marysville, Utah, is as follows
S03 Al20j Fe203 P20f, K20 Na20 H20+ H20- Si02 Total 38 34 37 18 tr 58 xo 46 33 12 90 09 22 too 10
Alunite occurs in hexagonal crystals (ditrigonal scalenohedral class), with an axial ratio of i i 252 The natural crystals are nearly always simple rhombohedrons, R(ioTi), or R modified by other rhombohedrons and the basal plane Because the angle between the rhombohedral faces is about 90° (90° 50') , the habit of the crystals is cubical The mineral also occurs massive, with fibrous, granular or porcelain-like structure
Alunite is white, pink, gray or red, and has a white streak It is transparent or translucent and has a vitreous or nearly pearly luster. Its cleavage is distinct parallel to oP(oooi), and it has an uneven, con- choidal or earthy fracture Its hardness ib 3 5-4 and its density 26-275. Its indices of refraction for yellow light are: €sasiS92, 572
Before the blowpipe the mineral decrepitates, but is infusible In the closed tube it yields water and at a high temperature sulphurous and sulphuric oxides Heated on charcoal with Co(NOs)2 it gives the blue color characteristic of Al20a It also gives the sulphur reaction It is insoluble in water but is soluble in H2S04 When ignited it gives off all its water and three-quarters of its S04, the other quarter remaining in &2S04 When the igmted residue is treated with water, the potas- sium sulphate dissolves and insoluble Al20s is left. It is upon this latter reaction that the economic utilization of the mineral depends,
The mineral is characterized by its color and hardness together with the reactions for AljHgO and sulphuric acid
Sulphates 245
Synthesis — Crystals have been made by heating an excess of alu- minium sulphate with alum and water at 230°
Occurrence anl Ongm— The mineral occurs m seams or veins in acid lavas It is thought to have been formed in some instances by the action of sulphurous vapors upon the rock forming the vein walls, in other instances by direct precipitation from ascending magmatic waters, and in others by the action of descending BfeSC
Localities — The principal known occurrences of alumte are at Tolfa, Italy, at Bulla Delah, New South Wales, on Milo, Grecian Archipelago, and at Mt Dore, France
In the United States it is found with quartz and kaolin in the Rosita Hills, and the Rico Mts,, Colo , in the ore veins at Silverton and Cripple Creek, Colo , as a soft white kaolin-like material in the ore veins at Goldfield, Nev , as a crystalline constituent in the rocks at Goldfield, Nev , and Tres Cerntos, Cal , and in the form of a great vein of comparatively pure material at Marysville, Utah
Uses — In Australia alumte is calcined and then heated with dilute sulphuric acid. The mixture is then allowed to settle and the clear solution is drawn off and cooled Alum crystallizes The mother liquor which contains aluminium sulphate, after further treatment with the calcined mineral, is evaporated and the aluminium salt separated by crystallization In the United States it is now (1916) being utilized as a source of potash and aluminium
Brochantite ((CuOH)2S04 2Cu(OH)2) occurs in groups of small prismatic crystals, in fibrous masses and in drusy crusts Its crystal- lization is orthorhombic with a b £-.7739 i ; 4871 and the angle 1 10 A no =75° 28' Cleavage is perfect parallel to oopas (oio). The mineral is emerald-green to blackish green and its streak is light green. It is transparent or translucent, and its luster is vitreous, except on cleavage planes where it is slightly pearly Its hardness is 3 5-4 and density 3 85 In the closed tube it decomposes, yielding water and, at a high temperature, sulphuric acid. It gives the usual reactions for copper and sulphuric acid Brochantite occurs in the upper portions of copper veins at many places, in some of which it was formed by the interaction between silicates and solutions of copper salts. In the United States it has been foi}nd at the Monarch Mine, Chaffee Co , Colorado, at the Mammoth Mine, Tmtic District, Utah, and in the Clifton-Morenci Mines, Arizona,
246 Descriptive Mineralogy
Hydrous Sulphates
The hydrous sulphates comprise a numbei of sulphates combined with water Among them are the normal salts miralnhte or glauber salt (Na2S04 loEfeO), gypsum (CaSQi 2H/)), the epwmilc and inclan- tertte groups (R//S04 7H20), chakanttnte (CuS04 sEbO), md the alum group (R'A1(S04)2 i2H20), kiesente (MgSOi H2O), polyhalite (K2MgCa2(S(X)4 H20), and a number of basic compounds Several of them are of considerable economic importance, They are separated into a normal group and a basic group,
Hydrated Normal Sulphates
The hydrated normal sulphates occur in crystals, and most of them are found also in beds mterstratified with other compounds that arc known to have been precipitated by the evaporation of sea water or the water of salt and bitter lakes All are soluble in water
Mirabdite, or glauber salt, (Na2SOt loHaO) is a white, trans- parent to opaque substance occurring m monoclmic crystals or as efflorescent crusts Its hardness is i 5-2 and specific gravity i 48 It is soluble in water and has a cooling taste When exposed to the air it loses water and crumbles to a powder Mirabihte occurs at the hot springs at Karlsbad, Bohemia and is obtained from the water of many of the bitter lakes m California and Nevada Its crystals are deposited from a pure solution of Na2S04 If the solution contains NaCl, how- ever, thenardite (Na2S04) deposits
Kieserite (MgS(>4 H20) occurs commonly m granular to compact, massive beds mterstratified with halite and other soluble salts at Stass- furt, Germany, and at other places where ocean water has been evap- orated. It is believed to have resulted from the partial desiccation of epsomite (MgS04 ?H20), though it may be deposited from a solution of MgSO* m the presence of MgCfe. Kiesente is white, gray, or yellow- ish, and is transparent or translucent It forms sharp bipyraimdal monoclmic crystals Its hardness is 3 and its density 2 57* In the presence of water it passes over into epsomite and dissolves, yielding a solution with a bitter taste. Large quantities are utilized in the fer- tilizer industry
When exposed to the air it becomes covered with aa opaque crust*
Sulphates
Gypsum (CaSO4 2H20)
Gypsum is the most important of all the hydrous sulphates It occurs in massive beds a'vociated with limestone, m crystals, in finely granular aggregates and in fibrous masses, under a great variety of conditions
Theoretically, it consists of 46 6 per cent 80s, 32 5 per cent CaO and 20 9 per cent EfeO, but usually it contains also notable quantities of other components, especially Fe203, AbOa and 8162 Clay is a common im- purity in the massive varieties
The analyses of two commercial gypsums follow
CaSCXt H20 Si02 A1203 CaC03 MgC03 Total 78 40 19 96 35 12 56 57 99 96 78 51 20 96 05 08 ii 99 71
Dillon, Kans Alabaster, Mich
The crystals are monoclmic (prismatic class), with a : b =.6895 : i 4132 and j8=8i° 02' They are usually developed with a tabular habit due to the predominance of oo P OD (oio) The prism oo P(iio),
Fig 139 Fig 140
FIG 139 — Gypsum Crystals with wP, no ooPoo, oio (ft), — P, in (/) and
FIG 140 — Gypsum Twinned about oo P 55 (100) Swallow-tail Twin Form mt
I and b as in Fig 139
and pyramid +P(ixI) are also nearly always present (Fig 139). Often the +P faces are curved, producing a lens-shaped body Twinning is very common, giving rise to two types of twinned crystals In the most common of these oo P 56 (100) is the twinning plane and the resulting twin has the form of Fig 140 In the second type -P 66 (101) is the twinning plane (Fig. 141) Forms of this type are frequently bounded by +P(iiT), -P(iii), oo (103), and °OP65 (100) When the side
Descriptive Mineralogy
faces are curved the well known arrowhead twins result (Fig 141)
The angle noAiTo=68° 30'
The mineral possesses a good cleavage parallel to oo P (oio)
yielding thin inelastic fohae, another parallel to +P(Tn) and a less
perfect one parallel to oo P 66 (100) It is white, colorless and transpar- ent when pure, gray, icd, yellow, blue or black when impure Its hardness is i 5-2 and sp. gr 32 The luster of crystals is pearly on oo P ob (oio) and on other surfaces vitreous Massive varieties are often dull The refractive indices for yel- low light are, 1.5205, 1.5226,
FIG 141— Gypsum Twinned about S29
-P5(ioi) Forms 100 In the closed tube the mineral (a), -P, in (/), P, nl and gives off watei and falls into a white J P 55 , Io3 (e) Arrow head Twm powder (see p 238) It colors the
flame yellowish red and yields the sul- phur test on a silver coin. It is soluble m about 450 pts of water and is readily soluble in HC1 When heated to between 222° F and 400° F it loses water and disintegrates into powder, which, when ground, becomes " plaster of Pans " This, when moistened with water, again combines with it and forms gypsum The crystallization of the mass into an aggregate of interlocking crystals constitutes the " set."
Gypsum is distinguished from other easily cleavable, colorless min- erals by its softness and the reactions for S and EfeO.
The varieties of gypsum generally recognued are.
Syenite, the transparent crystallized variety,
Safanspar, a finely fibrous variety,
Alabaster, a fine-grained granular variety, and
Rock-gypsum, a massive, structureless, often impure and colored variety.
Gypsiie is gypsum mixed with earth
Syntheses — Crystals of gypsum separate from aqueous solutions of CaSO* at ordinary temperatures, and also from solutions saturated with Nad and MgCk Some of these are twinned.
Occurrence and Origin — Gypsum forms immense beds interstrati- fied with limestone, clay and salt deposits where it has been precipitated by the evaporation of salt lakes Its crystals occur around volcanic vents, where they are produced by the action of sulphuric acid on cal-
Sulphates 249
careous rocks. They are also found isolated in clay and sand, and in limestone, wherever this rock has been acted upon by the sulphuric acid resulting from the weathering of pynte Gypsum also occurs in veins and is found in New Mexico in the form of hills of wind-blown sand
Localities — Crystals are found m the salt beds at Bex, Switzerland, in the sulphur mines at Girgenti, Sicily, and at Montmar-tre, France In the United States they occur at Lockport, N Y , in Trumbull Co , Ohio, and in Wayne Co , Utah, in limestone, and on the St Mary's River, Maryland, in clay
Extensive beds occur in Iowa, Michigan, New York, Virginia, Ten- nessee, Oklahoma and smaller deposits in many other states, and wind- blown sands in Otero Co , New Mexico
Uses — Crude gypsum is used in the manufacture of plaster, as a retarder in Portland cement, and as a fertilizer under the name of land plaster The calcined mineral is used as plaster of Pans and in the manufacture of various wall finishing plasters, and certain kinds of cements Small quantities are used in glass factories, and as a white- wash, a deodorizer, to weight phosphatic fertilizer, as an adulterant in candy and other foods, and as a medium for sculpture
Production — The quantity of gypsum mined in the United States during 1912 aggregated 2,500,757 tons, valued at $6,563,908 in the form in which it was sold Of this amount, 441,600 tons of crude material, valued at $623,500 were sold ground, and 1,731,674 tons, valued at $5,- 940,409, were calcined The output of New York was valued at $1,241,- 500, that of Iowa at $845,600 and of Ohio at $812,400
After the United States the next largest producer is France with a product in 1910 of 1,760,900 tons, valued at $2,942,600 and Canada with 525,246 tons, valued at $934,446
Epsomite And Vitriol Groups
These groups comprise minerals with the general formula RSO-i 7HkO, in which R=Mg, Zn, Fe, Ni, Co, Mn and Cu Isomorphous mix- tures indicate that the compounds are diomorphous, and that the group is, therefore, an isodimorphous group. The group is separable into two divisions, of which one, the epsomite group, crystallizes in the bisphenoidal class of the orthorhombic system with axial ratios approx- imating i : i ' ,565 The other division, the vUriol9 or mdanterite, group crystallizes in the prismatic class of the monochmc system with axial ratios approximating 1 18 ' i ' i 53 and ft approximating 75° Only the magnesium compound among the pure salts is known to crys- tallize in both systems. Crystals separated from a saturated solution
250 Descriptive Mineralogy
are orthorhombic, while those separated from a supersaturated solution are monoclimc Other salts occur in isomorphous mixtures in both systems All members of the group are soluble in water and all occur as secondary products formed by decomposition of other minerals.
Epsomite (MgSO4 7H20)
Epsomite, or Epsom salt, usually occurs in botryoidai masses and fibrous crusts coating various rocks over which dilute magnesium sul- phate solutions trickle, and mingled with earth in the soils of caves The solutions result from tke act10n upon magnesian rocks of sulphuric c,cid derived from oxidumg sulphides Crys- tals are rare
The composition corresponding to MgSOr yHkO demands 32,5 SOa, 163 MgO and 51 2 H20
The mineral forms white or colorless bi- Ho 142-EpsomitcCrys- sphenoidalj orthorhombic crystals, with an tal with OQ P 1 10 (m) , , . -,,
p axial ratio a b ' 9901 i S7°9 Their
and -r, in (s) habit is tetragonal The angle no A 10=89°
26' The commonest forms occurring on syn-
P P
thetic crystals are combinations of ooP(iio), and -T(III) or -~J(ni)
(Fig 142) Natural crystals contain, m addition oo P 56 (oio) and POO(IOI)
The luster of epsomite is vitreous, its hardness 2 0-2 5 and specific gravity 170 Its refractive indices for yellow light are a —143 25, 0=i 4554 and i 4°°8
The mineral is soluble m water, yielding a solution with a bitter taste With a solution of barium chloride it yields a white precipitate of BaSOt
Epsomite is distinguished from other colorless, soluble minerals by its taste and the reactions for S and Mg
Synthesis —Crystals are produced by evaporation of solutions of MgSO* containing certain other salts From those containing borax, crystals of the type indicated above are separated The production ot right or left crystals may be provoked by inoculation of the solution with a particle of a crystal of the desired type
Locakties — Epsomite occurs m mineral waters, as, for instance, at Seidlitz, Bohemia, on the walls of mines and caves, among the deposits of bitter lakes, and as crystals m the soil covering the 'floors of caves
Sulphates 251
Melantente, 01 copperas (FeSO4 7H20), is usually m fibrous, stalactitic or pulverulent masses associated with pynte or other sul- phides containing iron, from which it was produced by weathering processes It is commonly some shade of green Its streak is colorless Its crystals, which are monochmc (prismatic class), are rare The mineral has a hardness of 2 and a density of i 9 It is soluble in water, forming a solution which has a sweetish astringent taste.
Alum Group
The alum group includes a large number of isomorphous compounds with the general formula R'A1(S04)2 laHsO The group crystallizes in the isometric system (dyakisdodecahedral class), but all of its mem- bers are so readily soluble m water that they are rarely found in nature The commonest alums are kalmite (KA1 (864)2 I2H20) and soda alum (NaAl(S04)2
Double Sulphates With Carbonates Or Chlorides
A number of compounds of sulphates with chlorides and carbonates are known, but of these only one is of any great economic importance Two others afford interesting crystals The commercial compound is kaimte, which is a hydrated combination of MgS04 and KC1, with the formula M&S04 KC1 3H20 The other two best known members of the group are leadhillile (PbSO4 Pb(PbOH)2(COs)2 and hanksite (2Na2C03 QNa2S04 KCI)
Kainite (MgSO4 KCI 3H20)
Kaimte is found only in beds associated with halite and other deposits from saline waters It is rarely crystallized Crystals are monoclmic (prismatic class), with a b c=i 2186 : i . 5863 and £=85° 6'. They possess a pyramidal habit with oP(ooi) and dbP(ni)(iiT) predom- inating
The mineral usually forms granular masses which are white, yellow, gray or red It is transparent, has a hardness of 2 and sp gr 2.13, and is easily soluble in water Its refractive indices for sodium light are- 01=14948 and 7*1.5203
When heated in a glass tube it yields water and HC1 It is distin- guished from other soluble minerals by this reaction, and by the fact that it yields the test for sulphur, and colors the flame blue when its powder is mixed with CuO and heated before the blowpipe
252 Descriptive Mineralogy
Synthesis — Crystals have been produced by evaporating a solution of K2S04 and MgSOi containing a great excess of MgCb
Occurrence — Kaimte occurs in the salt beds of Stassfurt, Germany, and of Kalusz in Gahcia, and in the deposits of salt lakes and lagoons It also occurs as crusts on some of the lavas of Vesuvius
Uses.— The mineral is utilized as a source of potassium m the manu- facture of potassium salts and fertilizers Large quantities are imported annually into the United States In 1912 the imports aggregated 485,132 tons, valued at $2,399,761
Hanksite (2Na2CO3 pNa2SOi KC1) occurs almost exclusively in
. hexagonal prisms that are prismatic or tabular,
or in double pyramids suggesting quartz crys- tals Their axial ratio is i . i 006 The com- monest crystals are bounded by oP(oooi), FIG 143— Hanksite Crys- ooP(ioTo), P(ioTi) (Fig. 143) and 2P(202i), tal with OOP, joio (w), or |p(4o4s) Their cleavage is imperfect P, ion (0) and oP, oooi pM op(oool) Thc mmeml fe white Qr
yellow Its hardness -2 and its specific gravity =256 It is soluble m water. Its refractive indices are w=i 4807 and €=i 4614 It occurs at Borax Lake and Death Valley, California, in the deposits of salt lakes
LeadhUlite (PbSO4 Pb(PbOH)2(CO,<02) occurs principally as crystals m the oxidized zones of lead and silver veins The crys- tals are monoclmic (prismatic class), and have an hexagonal habit. Their axial ratio is i 7515 11:2 2261. j9=89°32'. The principal forms observed on them are oP(ooi), oo'P(no), ooP<w (too), P(m) and £P6o (102) In the most common twins ooP(no) is the twin- ning plane The mineral is white or yellow, green or gray, and it is transparent or translucent Its streak is colorless It is sectile, has a hardness of 2 5 and a specific gravity of 6.35 Before the blowpipe it mtumesces, turns yellow, and fuses easily (i 5) Upon cooling it again becomes white It effervesces m HNOs and leaves a white precipitate of PbS04 It reacts for sulphur and water It is found at Leadhills, Scotland, and Mattock, England, associated with other ores of lead; at a lead mine near Iglesias, Sardinia, and at several silver-lead mines in Arizona.
Chapter Xiii
The Chromates, Tungstates And Molybdates
The Chromates
The only chromate of importance, among minerals, is the lead salt of normal chromic acid, HkCrO* There are several other chromates known, but they are basic salts and are rare All are lead compounds The normal salt, PbCrO*, is known as crocoite Chromic acid is un- known, as it spontaneously breaks down into CrOa and water when set free from its salts Its best known compound is potassium chromate,
Crocoite (PbCr04)
Crocoite is well characterized by its hyacinth-red color It is a lead chromate with PbO=68 9 per cent and 003=31 i per cent.
Its crystallization is monoclmic (prismatic class) with a . b : c 9603 : i . 9159 and 0=77° 33'- Its crystals, which are usually im- planted on the walls of cracks in rocks, are prismatic or columnar parallel to ooP(no) Their pre- dominant forms are ooP(no), — P(iu), and various domes (Fig 144). Their* cleavage is distinct parallel to ooP(uo) The angle 1 10 A no=860 19' The mineral also occurs in granular masses
Crocoite is bright hyacinth-red, and is translucent Its streak is orange-yellow The mineral is sec- tile Its fracture is conchoidal, its hardness 2.5-3 and density about 6 is about 2 42,
In the closed tube it decrepitates, and blackens, but it reassumes its red color when heated On charcoal it deflagrates and fuses easily,
FIG 144 —Crocoite Crystals with no (m), cop}, 120 (/), -P, in 0), 3Po5, 301 PS5, Tor (£), oP,
001 (C), P>,Oii 2? Co, 021 (?)
and iPSb,oi2 (w)
Its intermediate refractive index
254 Descriptive Mineralogy
yielding metallic lead and a lead coating With minocosmic salt it gives the green bead of chromium
The mineral is easily lecogmzed by its color and the test for chro- mium
Synthesis — Crystals, like those of crocoite, have been obtained by heating on the water bath a solution of lead nitrate in nitric acid and adding a dilute solution of potassium bichromate
Occurrence — Crocoite occurs under conditions which suggest that it is a product of pneumatolysis
Locahhes — It is found in the Urals, at Rezbanya and Moldawa, m Hungary, m Tasmania, and m the Vulture Mining district, Mancopa Co , Arizona,
The Tungstates And Molybdates
The tungstates are salts of tungstic acid, EfoWC They are the principal sources of the metal tungsten which is beginning to have im- portant uses The molybdates are salts of molybdic acid, liaMoOt The two most prominent tungstates arc ideditc, CaWQi, and wolf- ramite (Fe Mn)W04, and the most prominent molybdate is wulfenite, PbMoO*
All tungsten compounds give a blue bead with salt of phosphorus in the reducing flame When fused with NagCOa, dissolved in water and hydrochlonc acid, and treated with metallic zinc (see pp 482, and 492 for details of test), they also yield a blue solution which rapidly changes to brown
The molybdates give with the salt of phosphorus bead in the oxidis- ing flc,me a yellow-green color while hot, changing to colorless when cold. In the reducing flame the color is clear green.
Scheelite Group
The scheelite group comprises a series of tungstates and molybdates of Ca, Cu and Pb The minerals arc tetragonal and hcmihcdral and are all well crystallized The more important members of the group are scheehte and wulfemte CuprotungMe is a copper tungstate (CuW04) and stolzite a lead tungstate
Scheelite
The formula of scheelite demands 80 6 per cent WO.?, and 194 per cent CaO, but the mineral usually contains a little molybdenum in place of some of the tungsten It nearly always contains also a little Fe.
Chromates, Tungstates And Molybdates 255
Scheehte crystallizes in the tetragonal bipyraimdal class Its crys- tals are usually pyramidal, though often tabular m habit Their axial ratio is i : i 5268 On the pyramidal types the predominant planes are pyramids of the first, second (Fig 145), and third orders and on the tabular types, in addition, the basal plane One of the most familiar
combinations is P(m),P co (101), y (313) and lj(i3i) (Fig 145),
Other forms frequently found on its crystals are oo (102) and £P °° (105) The angle no A In 79° SSi' Twinning is common, both contact and penetration twins having oo p oo (100) as the twinning plane The mineral aJbO occurs m remform and granular masses
Scheehte is white, yellow, brown, greenish or reddish, with a white
Fig 145 Fig 146
FIG 145 — SdiceliLc CryoUl with P, in \pjt P oo , 101 (e) and oP, ooi (c), FIG 146 — Scheehte Crybtal with and e as in Fig 145 Also I I , 313 (h) and
streak and vitreous luster It has a distinct cleavage parallel to P(ooi), and an uneven fracture It is brittle, has a hardness of 4 3-5 and a density of about 6, and is transparent or translucent It is soluble in HC1 and HNOs with the production of a yellow powder, tungsten tri- oxide, which is soluble m ammonia Its refractive indices are i 9345, i 9185 for red light
Before the blowpipe the mineral fuses to a semitransparent glass With borax it forms a transparent glass which becomes opaque on cooling With salt of phosphorus it yields the characteristic beads for tungsten, but specimens containing iron must be heated with tin on charcoal before the blue color can be developed
Scheehte is distinguished from limestone, which its massive forms closely resemble, by its higher specific gravity and the absence of effer-
256 Descriptive Mineralogy
vescence with HC1 From quartz it is distinguished by its softness and from bante by greater hardness and higher specific gravity
Syntheses —Crystals of scheehte have been made by adding a solu- tion of sodium tungstate to a hot acid solution of CaCk, and by fusing the two compounds They have also been produced by fusing wolfram- ite with CaCl2
Occurrence and Origin — Scheehte is found m gold-quartz veins and in veins cutting acid igneous rocks, where it is associated with cassiterite, topaz, fluorite, molybdenite, wolframite and many other metallic compounds, and as a contact metamorphic product in altered limestone intruded by granite It is probably m all cases a deposit from hot solutions
Localities — It occurs at Zinnwald, Bohemia, Altenbeig, Saxony, Carrock Fells, Cumberland, England, Pitkaranta, Finland, in New Zealand, and in the United States at Monroe and Trumbull, Conn , in the Atoha District, Kern Co , California, the Mammoth Mining Dis- trict, Nevada, in Lake County, Colorado, near Gage, New Mexico, where it occurs with pynte and galena in a vein cutting limestone, and in the placer gravels at Nome, Alaska
Uses of Tungsten —Tungsten is used puncipally m the manufacture of tool steel, electric furnaces and targets for Ronlgen rays It is employed also as filaments m electric-light bulbs, in the manufacture of sodium tungstate which is used for fireproofing cloth, as a mordant in dyeing, and for a number of other minor purposes
Production — Scheehte has been mined in small quantity m Idaho, Alaska, California, Nevada, Arizona, and New Mexico, Us a source of tungsten, but most of this element has heretofore been produced from other compounds, mainly wolframite In 1913 a few hundred tons of scheehte concentrates were produced m the Atoha district, California, and the Old Hat district, near Tucson, Ariz. At present (rgi6) it is being produced in large quantity near Bishop, Inyo Co., Cal.
Stolzite (PbWO4) is completely isomorphous with wulfenite. Its crystals, which are pyramidal or short columnar, arc mainly combina- tions of °oP(no), P(in), 2P(22i) and oP(ooi) Their axial ratio is i . i 5606
The mineral is gray, brown, green or red. It is translucent and has a white streak Its hardness is 2 75-3 and its sp. gr 7.87-8.23. Its refractive indices for yellow light #re- w 2685, € 2 182
Before the blowpipe it decrepitates and melts to a lustrous crystal- line globule. The bead with microcosmic salt in the reducing flame
Chromates, Tungstates And Molybdates 257
is blue when cold, in the oxidizing flame it is colorless The mineral is decomposed by HNOs leaving a yellow residue ol WOs Crystals have been made by fusing sodium tungstate and lead chloride
Its principal localities are the tm-bearing veins at Zmnwald, Bo- hemia, the copper veins in Coquimbo, Chile, and Southampton, Mass , where it is associated with other lead compounds
Wulfenite (PbMoO4)
Wulfemte is the only molybdate of importance that occurs as a mineral Its formula demands 39 3 MoOs and 60 7 PbO Calcium sometimes replaces a part of the Pb and tungsten a part of the Mo.
Wulfemte is hemihedral and hemimorphic (tetragonal pyramidal class) Its crystals are more frequently tabular than those of scheelite, and they are usually very thin
The mineral, however, occurs also m pyramidal and prismatic crys- tals which, in some cases, exhibit distinct hemunorphism Their axial
Fro 147 FIG 148
FIG 147 — Wulfemte Crystal with °o P , 100 (a) and °o , i o 12 (0)
FIG 148 — Wulfenite Crystal with oP, ooi (c), JPoo, 102 P°°, 101 (e),
P, in (M) and JP, 113 (s)
ratio is a ' c=i . i 5777 The most common forms found on its crys-
r oo pal tals are oP(ooi), P(ni), —j1 (320), fP(ii3) and POO(IOI) (Fig
147 and 148). The angle in /\1n So° 22'.
The cleavage, parallel to P, is very smooth, and the fracture is con- choidal The mineral is brittle Its hardness is about 3 and specific gravity about 6 8 Its luster is resinous or adamantine, and its color orange-yellow, olive-green, gray, brown, bright red or colorless Its streak is white and it is transparent For red light, 2 402, 2 304
Before the blowpipe wulfenite decrepitates and fuses readily With salt of phosphorus it gives the molybdenum beads With soda on charcoal it yields a lead globule. When the powdered mineral is evap- orated with HC1 molybdic oxide is formed On moistening this with water and adding metallic zinc an intense blue color is produced.
Wulfenite is distinguished from tanadmtte (p 271), by crystalliza- tion, by the test for chlorine (vanadimte) and the test for tungsten.
258 Descriptive Mineralogy
Synthesis — Wulf emte crystals have been produced by melting together sodium molybdate and lead chloride
Occurrence and Localities — The mineral occurs in the oxidized zone of veins of lead ores at some of the principal lead occurrences in Europe, and in the United States near Phoenixville, Pennsylvania, in the Organ Mountains, New Mexico, at the mines in Yuma County, Arizona, at the Mammoth Mine, m Pmai County in the same State, and at many other of the lead mines m the Rocky Mountain states
Uses — Wulfenite is an important source of molybdenum, but, because of the few uses to which this metal is put, the amount of wulfen- ite mined annually is very small
WOLFRAMITE GROUP Wolframite ((Fe MnJWO*)
Wolframite is the name given the isomorphous mixtme of the man- ganese and iron tungstates that occur neaily puu* in some vanctics of the mineials hubnente and fcrbente
The mixture of the uon and manganese molecules is more common than either alone, consequcntl} wolframite is the commonest member of the group. The properties of all three mmcials, ho\ve\cr, arc so nearly alike that they must be distinguished by chemical analysis
The name wolframite is usually applied to mixtures of the tungstates in which the proportion of Fe to Mn \uries between 4 : i and 2 3, or between g 5 per cent and 189 per cent of FeO and 14 pci cent and 4 7 per cent of Mn02.
It has recently been suggested that the name ferbente be limited to mixtures containing not more than 20 per cent of the hubnente mole- cule and the name hubnerite to those containing not more than 20 per cent of the ferbente molecule This would leave the name wolframite for mixtures containing more than 20 per cent of both FcW04 and MnW04
Analyses of specimens of hubnente (I), wolframite (II and III) and ferbente (IV) follow
W03 FeO MnO CaO Other Total
I Ellsworth, Nye Co , Nev 7488 56 2387 .14 16 9961
II Sierra Cordoba, Argentine 7486 1345 ".°2 , 122 10055
III Cabarrus Co , N C . 7579 1980 5.35 .32 tr 101.26
IV, Kwnbosan, Japan 75 47 24 33 tr tr 99.80
All members of the group crystallize m the monoclinic system (prismatic class) with axial ratios as follows
Chromates, Tungstates And Molybdates 259
Ferbente a . b 8229 i Wolframite 8300 i
Ilubmtite =8315 i
8463 0=89° 38' 8678 0=89° 38' 8651 0=89° 38'
The crystals are pusmatic or cubic in habit and are bounded by
ooP(uo), ooPooJioo), and two 01 more of the following oP(ooi),
oo P .56 (oio), oo P2(2io), P oo (on), -]P 66 (To2), - JP 66 (102), -P(in),
- 2?2(i2i) and +2P oo (102) (Fig 149) The
angle iioAiio for ferbente 78° 51', for wol
frcimite 79° 23', and foi hubnente 79° 29'
Twins are fairly common, with oo P 66 (100)
the twinning plane Cleavage is perfect
parallel to oo P 03 (oio) The minerals also
occur m lamellar and granular masses
Hubnente is brownish red to black and translucent, wolframite is black and trans- lucent only on thin edges, and ferbente is '49 -Wolframite Crys- , . . / ' . .. tal with oop, no (m),
black and opaque. The streak is yellow to oopj, 2io (/) oopoo
yellowish brown in hubnente and brown or 100(0), — JPoo, 102 (/), brownish black in ferbente, with the streak P, 011 (/), — 2Fa,iai of wolframite between +ip55> i°* (y) and
Wolframite is buttle, has a hardness ot IIX W 5-5 5, a specific gravity of 72-75, and a submetallic luster Before the blowpipe it fuses to a globule which is magnetic Fused with soda and niter on platinum it gives the bluish green manganate. The salt of phosphorus bead is reddish yellow when hot and a paler tint when cold. In the reducing flame the bead becomes dark red If the mineral is treated first on charcoal with tin its bead assumes a green color on cooling. The mineral dissolves in aqua regia with the production of the yellow tungsten trioxide When treated with concentrated HgSOi and zinc it yields the blue tungsten reaction
Crystals of wolfiamite are easily distinguished from crystallized colnmbiie (p 293), samarskite (p. 295), and uraninite (p 297), by dif- ferences in crystallization Massive wolframite is distinguished from massive forms of the other three minerals by its more perfect cleavage and by the reactions with the beads Uranmite, moreover, contains lead Wolframite is distinguished from black tourmahne (p. 434) by the differences m specific gravity,
Occurrence and Ongin — Wolframite usually occurs in veins with tin ores, and in quartz veins with various sulphides, and in pegmatite. Its origin is probably pneumatolytic.
260 Descriptive Mineralogy
Localities —Wolframite is found m all tm-producmg districts, espe- cially at Zmnwald, Schneeberg and Freiberg, in Germany, at Ner- chinsk, in Siberia, m Cornwall, England, at Oruro, in Bolivia, and at various points in New South Wales, Australia
In the United States it occurs at Monroe, Conn , near Mine La Motte, Missouri, near Lead, South Dakota, where it impregnates a sandy dolomite, and at Hill City in the same State in quartz veins, sometimes containing cassitente, in Boulder Co , Colorado, in veins m granite (ferbente), neai Butte, Montana, in quaitz veins carry- ing silver ores (hubnente), and the quartz-cassitcnte veins near Nome and on Bonanza Creek, in Alaska, and in quarts veins at various points in Washington, Idaho, California, Nevada, New Mexico and Arizona At some of these localities the mineral is more properly hubnente
One or another of the three has been mined in Colorado, Nevada, South Dakota, Montana, Washington, Calif oinu, Aiizona, and New Mexico, but the total production has never been laige Some of the ore shipped has been obtained from placers along streams that dram regions containing the mineral m veins, but most of it has been obtained from vein rock which is crushed and concentrated
Uses — These three minerals constitute the principal source of tung- sten used in the arts The uses of the metal are referred to under scheehte
Production — The total production of concentrates containing 60 per cent WOs in the United States during 1913 was 1,325 tons, valued at $640,500. Of this, 953 tons were ferberite from Boulder Co., Colorado A little hubnente was produced in the Arivica region, m southeast California, at Dragoon, Arizona, at Round Mountain, Nevada, and on Paterson Creek, Idaho. In addition, there were imported $86,000 worth of tungsten-beaimg ores and $143,800 worth of tung- sten metal and ferro-tungsten. The world's production of tungsten ore in 1912 was 9,115 tons.
Chapter Xiv The Phosphates, Arsenates And Vanadates
THE phosphates are salts of phosphoric acid, HsPO the arsenates of the corresponding arsenic acid, HsAsO and the vanadates of the corresponding vanadic acid, HaVC The phosphates are by far the most important as minerals They are easily distinguished by yielding phosphme, HsP, upon igniting with metallic magnesium and moistening the resulting Mg3P2 with H20 or HC1 (Mg3P2+6HCl=3MgCl2+ 2PHs) The gas is recognized by its disagreeable odor The arsenates are detected by the test for arsenic
The arsenates, phosphates and vanadates form groups of isomor- phous compounds, the most important of which is the apatite group Those occurring as minerals are divisible into several subgroups, of which the following six contain common minerals, viz (i) anhydrous (a) normal salts, (V) basic salts and (c) acid salts, and (2) hydrous (a) normal salts, (b) basic salts and (c) acid salts
A number of the phosphates and arsenates are of value commercially either because of the phosphorus they contain, because they are sources of valuable metallic salts, because they serve to indicate the presence of other valuable compounds, or because they possess an ornamental character
Nearly ail the phosphates are transparent or translucent and all are nonconductors of electricity or are very poor conductors,
Anhydrous Phosphates, Arsenates And Vanadates
Normal Phosphates, Arsenates And Vanadates
The minerals belonging in this class of compounds are not as numer- ous as the basic salts, but some of them are of great value The class includes phosphates of yttrium, the alkalies, beryllium, cerium, mag- nesium, iron and manganese and a group of isomorphous phosphates, arsenates and vanadates— -the apatite group— in which a haloid radicle replaces one of the hydrogen atoms of the acids Apatite, the prin- cipal member of the group, is an important source of phosphoric acid
262 Descriptive Mineralogy
Triphylite— (Li(Mn Fe)PO4)— Littuophilite
Triphylite is the name usually applied to the isomorphous mixture of LiFeP04 and LiMnP04, m \which the manganese molecule is present in small quantity only The mixture containing a large excess of the manganese molecule is called lithiophihte
The pure tnphyhte molecule contains FeO=45 5 Per cent, LigO 9 5 per cent and P2Ch=45 per cent The pure lithiophilite molecule consists of 45 i per cent MnO, 9 6 per cent Li20 and 45 3 per cent
P205
Both substances are orthorhombic (bipyramidal class), with an axial ratio approximating 4348 " i : 5265 Crystals are rare and not well developed They are usually rough prisms bounded by ooFoo (oio), oP(ooi), ooP(no), ooP2(i2o) and 2Po6 (021) The minerals usually occur massive, or in irregular, rounded crystals, with two very dis- tinct cleavages
Both minerals are transparent to translucent, both have a white streak, and both are vitreous to resinous in lustci Thou baldness is about 4 5-5 and sp gr about 3 5 Triphylite is greenish gray to blue, and lithiophilite pink, yellow or brown The refi active indices for light brown lithiophihte are a=i 676, j3=i 679, 7=1 687, those for blue triphyhte are a trifle higher
When heated in closed tubes both compounds are apt to turn dark They fuse at a low temperature (i 5) and color the flame crimson In the case of tnphyhte the crimson streak is bordered by the green of iron. Lithiophilite gives the reactions for Mn Most specimens give reac- tions for all these metals — Fe, Mn and Li Both minerals are soluble inHCl
The two minerals are distinguished from other compounds by their reactions for phosphorus and lithium, and from each other by the reac- tions for Fe and Mn
Occurrence — They usually occur as primary constituents of coarse granite veins They are associated with beryl, tourmaline and other pneumatolytic minerals and with secondary phosphates, which are presumably weathering products of the pnmary phosphates
Locahties — Both minerals occur at a number of points associated with other lithium compounds, especially spodumene (p 378) In this country tnphylite has been found at Peru, Maine, Grafton, Hampshire, and Norwich, Massachusetts, lithiophihte at Branchville, Connecticut, and at Norway, Maine
Neither of the minerals possesses a commercial value at present.
Phosphates, Arsenates And Vanadates 263
Beryllonite (NaBeP04)
Beryllomte is a comparatively rare mineral occurring at only a few places and al\\tiys in crystals or in crystalline grams
Its composition is 24 4 per cent NaO, 19 7 per cent BeO and 55 9 per cent P2Cb
Its crystals are orthorhombic (bipyramidal class), with an axial ratio 5724 i 540° They are short pyramidal or tabular in habit, often exhibiting a pseudohexagonal symmetry. Most crystals are highly modified with oP(ooi), oo P 60 (100), oo P 66 (oio), P 66 (101) and 2P?(i2i), the principal forms Twins are common, with oo P(no) the twinning plane The crystal faces are frequently strongly etched
The mineral is white to pale yellow It has a vitreous luster, except on oP(ooi), where the luster is sometimes pearly It possesses four cleavages, of which the most perfect is parallel to oP(ooi). That parallel to oo P 60 (100) is distinct, but the others are indistinct Its hardness is 5 5-6 and its density 2 845 Its fracture is conchoidal Crystals often contain numerous inclusions of water and liquid C02 arranged in lines parallel to L Its refractive indices for yellow light are a=i 5520, jS=i 5579, 7=1 5608
Beiyllomte decrepitates and fuses in the blowpipe flame to a cloudy glass, at the same time imparting to the flame a yellow color It is slowly soluble in HC1, and gives the phosphorus reaction with mag- nesium
It is distinguished from most other colorless transparent minerals by the reaction for phosphorus, from other colorless phosphates by its crystallization and the sodium flame test
Occurrence and Localities — The best known occurrence of beryllo- nite m the United States is Stoneham, Maine, where it is found in the debris of a pegmatite dike associated with apatite (p 266), beryl (p. 359), and other common constituents of pegmatites It originally existed implanted on the walls of cavities in the pegmatite and was apparently the result of pneumatolytic processes
Use. — The mineral is used to some extent as a gem stone,
Monazite ((Ce Di La)PO4)
Monazite is the principal source of certain rare earths that are used m manufacturing gas mantles Although it occurs as small grams and crystals m certain granites it is found m commercial quantities only m the sands of streams.
264 Descriptive Mineralogy
The mineral is a phosphate of the metals cerium, lanthanum, praseo- didymium and neodidymium in most cases combined with the silicate of thorium Its composition may be represented by the formula
*((Cc La Di)P04)+(ThSi04),
in which the proportion of the second constituent varies from a trace to an amount yielding 20 per cent ThC>2 Since this is not constant in quantity it is not to be regarded as an essential portion pf the com- pound It is probable that in monazite we have to do with a solid solution of cerium and thorium phosphates, thorium silicate and oxides of the rare metals
Monazite is monochnic with a b : 9693 ' i : 9255 and 76° 20' Crystals are usually prismatic with the pinacoids oo P 56 (100), ooPob(oio), the prism ooP(no), the two domes — POO(IOI) and +P66(ioY) and the pyramids -P(in) and +P(nT) They are often flattened parallel to the orthopmacoid (Fig 150) The angle 1 10 A iTo= 86° 34'
Their cleavage is perfect parallel to oP The color of the mineral is gray, yellow, red- dish, brown or green It is usually transpar- ent or translucent and sometimes opaque It is brittle, has a white streak, and a resmous luster Its hardness is 5-5 5 and its sp gr FIG. 150— Monazite Ciys- 4 7-5 3, varying with the proportion of thorium tal with oo POO, ioo (a), nt The refractive indices for yellow
00 P. 110 (0Z), 00 ?2, , , 0 0
(,), oo P S, oxo hSht are a=I 7938, 7 - t 8452. -Poo, ioi (w), +Pco, The mineral is infusible Before the blow- iol (x) and P, nI pipe it turns gray, and when moistened with H2S04 it colors the flame bluish green It is
difficultly soluble in HC1 and HNOs Most specimens are strongly radioactive
Synthesis — Crystals of monazite have not been prepared, but crys- tals of cerium phosphate similar to those of monazite have been made by heating to redness a mixture of cerium phosphate and cerium chloride Occurrence and Ongvn — Monazite occurs as the constituent of cer- tain granites and granitic schists in small crystals scattered among the other components In this form it is a separation from the granitic magma When the granites are broken down to sand by weathering the monazite is freed and because of its specific gravity it concentrates in stream channels
Localities — Although the mineral is fairly widespread in the rocks,
Phosphates, Arsenates And Vanadates 265
it is concentrated into commercial deposits at only a few places. The most important of these are in southeastern Brazil, in Norway, and in a belt 20 to 30 miles wide and 150 miles long extending along the east side of the Appalachian Mountains from North Carolina into South Carolina
The mineral has also been reported from many points in ten coun- ties in Idaho Near Centerville it may be m sufficient quantity to be of commercial importance
Preparation — Monazite is separated from the valueless sand in which it is found, by washing, and the residues thus resulting are further concentrated by a magnetic process The commercial concentrates produced in this way usually contain from 3 to 9 per cent ThCfe, and their price varies accordingly
Production and Uses — Monazite is the chief source of thorium oxide used in the manufacture of incandescent gas mantles Formerly it was produced in large quantity in the Carohnas, the production m 1909 amounting to 542,000 Ib , valued at $65,032, and in 1905 to 1,352,418 Ib , valued at $163,908. All of this was manufactured into the nitrate of thorium in this country and the amount made was not sufficient to meet the domestic demand. Consequently, large quan- tities of the nitrate were imported In 1910-11 mining of the mineral m the Carohnas ceased and all the monazite needed has been imported since then The imports of thorium nitrate for 1912 were 117,485 Ib , valued at $225,386 and of monazite, an amount valued at $47,334
Xenotime (YPO4)
Xenotime, though essentially an yttrium phosphate, usually contains erbium and in some cases cerium. It occurs in tetragonal crystals and m rolled grains Its axid ratio is i 6177 and angle in A ill 55° 30' Its crystals are octahedral or prismatic and are bounded by oo P(iio),P(m), and in some cases by oo P oo (100) and 2P oo (201) (Fig 151) Their cleavage is perfect parallel to FIG 151 -Xenotime Crystals with OOP no
ooP(no) The mineral is brown, v "
pink, gray or yellow Its streak is a pale shade of the same color. It is opaque and brittle Its luster is vitreous or resinous, its hardness 4-5 and specific gravity 45 Its indices of refraction are: e=i8i, w=i 72
266 Descriptive Mineralogy
Xenotime is infusible, insoluble in acids and with difficulty soluble in molten microcosmic salt It is distinguished from zircon by its cleavage and inferior hardness
A variety of xenotime containing a small percentage of sulphates is known as hussakite
The mineral occurs in pegmatite veins, in granites and in the sands of streams It is found in pegmatite veins at Hittero, Moss, and other places in Norway, at Ytterby, Sweden, in the granites of Mmas Geraes, Brazil, and m the gold washings at Clarksville, Georgia, and many places in North Carolina, and in pegmatite veins in Alexander County in the same State
Apatite Group
The apatite group consists of a number of phosphates, arsenates and vanadates in which fluorine or chlorine takes the place of the hydroxyl in basic compounds Thus, fluorapatite is Ca4(CaF)(P04)s and chlor- apatite CaCaGXPOOs The group contains a number of important minerals, of which apatite is by far the most valuable These minerals are isomorphous, all crystallizing in the hemihedral division of the hex- agonal system (hexagonal bipyramidal class) The names, composi- tions and axial ratios of the most important are as follows
Fluorapatite Ca4(CaF)(PC>4)3 a c=i 7346
Chlorapatite CaCaClXPCWs a 7346+
PyromorpTtite Pb4(PbCl)(P04)3 a.c=i 7293
Mimetite Pb4(PbCl)(As04)3 0 . e-i : 7315
Vanadmite Pb4(PbCl)(V04)s a:c-i: 7122
Apatite (Ca4(Ca(F C1))(PO4)3)
Although fluorapatite and chlorapatite are distinct compounds with slightly different properties, nevertheless, because of the difficulty of discriminating between them without analyses, the name apatite is commonly applied to both This is justified because of the fact that the two compounds are completely isomorphous, and the mineral as it usually occurs is a iruxture, of both The ideal molecules comprising the two varieties of apatite have the following compositions
Fluorapatite CaO=5S5, F=3 8, P205=42 3 Chlorapatite CaO=53 8, Cl=6 8, P20s==4i o
Apatite is found in well defined crystals, sometimes very large These have a holohedral habit, but etch figures on their basal planes
Phosphates, Arsenates And Vanadates 267
reveal the grade of symmetry of pyramidal hemihednsm The min- eral occurs also massive, in granular and fibrous aggregates and less commonly in globular forms and as crusts
The crystals are usually columnar or tabular, with the hexagonal prism or pyramid well developed Although in some cases highly modified, most crystals contain only the oo P(iolo), P(ioTi) and oP(oooi) planes prominent, though £P(iol2) and 2P2(ii2i) are not uncommon as small faces (Figs 152 and 153) Their cleavage is indistinct, and their fracture often conchoidal
Apatite may possess almost any color In a few cases the mineral is colorless or amethystine and transparent, but in most cases it is trans- lucent or opaque and white, green, bluish, brown or red Its streak is
Fig 152. Fig 153
FIG 152 — Apatite Crystals with cop, ioYo (w), P, loTi (r), oP, oooi (c), JP,
iol2 (r) and oop2, 1120 (a)
FIG 153 — Apatite Crystal with m, %, r and c as in Fig 152 and 2?, 2021 (y), 4P|, 1341 3?J, 1231 GU), 2P2, nil (5), P2, 1122 (B) and oo?}, 1230 (A)
white and its luster vitreous to resinous Its hardness is 4 5-5 and sp gr between 3 09 and 3 39 The refractive indices of fluorapatite for yellow light are 6335, €=1.6316 and of chlorapatite, co=i 6667 Many specimens are distinctly phosphorescent Nearly all fluoresce in yellowish green tints, and all are thermo-electric
Apatite fuses with difficulty, tinging the flame reddish yellow The chlorapatite melts at 1530° and the fluorine variety at 1650° When moistened with H2S04 all varieties color the flame pale bluish green, due to the phosphoric acid Specimens containing chlorine give the brilliant blue color to the flame when fused in a bead of microcosmic salt that has been saturated with copper oxide Specimens containing fluorine etch glass when fused with this salt in an open glass tube The mineral also yields phosphme when ignited with magnesium, and it dissolves in HC1 and HNOs
268 Descriptive Mineralogy
Apatite is much softer than beryl (p 359)> which it closely resembles in appearance It is distinguished from calcite by lack of effervescence with acids and from other compounds by the phosphorus reaction
The vaneties of the mineral recognized by distinct names are
Ordinary apatite crystals or granular masses
Manganapatite, in which manganese partly replaces the Ca of ordi- nary apatite This is dark bluish green
Fibrous, conci etionary apatite Known also as phosphorite
Osteohte The earthy variety
Phosphate rock. A mixture of apatite, phosphorite, several hydrous carbonates and phosphates of calcium, and fragments of bone and teeth It is more properly a rock with a brecciated and concretionary structure The composition of typical deposits is represented by the following analysis of hard rock phosphate from South Carolina
CaO P205 C02 Fe203 Al20s MgO Insol Undet H20 Moist 50 08 38 84 65 96 3 07 30 49 2 46 2 96 07
Guano is a mixture of various phosphates, both hydrous and an- hydrous, calcite and a number of other compounds It is rather a rock than a mineral, as it has no definite composition
Syntheses —Crystals of fluorapatite have been made by fusing sodium phosphate with CaF2 and by heating calcium phosphate with a mixture of KF and KC1
Origin — The crystallized apatite was formed by direct separation from igneous rock magmas and by pneumatolytic action upon limestone The phosphorite variety and the phosphate in phosphate rock were probably produced by the solution of calcium phosphate and its later deposition from solution— the original phosphate having been furnished in many cases by the shells of mollusca, and by the action of phosphoric acid produced by the decay of organisms upon limestone In many cases phosphorite accumulated as a residual deposit in consequence of the solution of the calcite and dolomite from phosphatic limestone, leaving the less soluble phosphate as a mantle on the surface.
Occurrence — The mineral occurs in microscopic crystals as a com- ponent of many rocks, as large crystals in metamorphosed limestones, as a component of many coarse-grained veins, especially those composed of coarse granite and those in which cassiterite, magnetite, tourmaline, and other pneumatolytic minerals are found At a number of places aggregates of apatite and magnetite or ilmemte occur in such large masses as to be worthy of being called rocks An impure apatite in concretionary and fibrous forms also occurs in thin beds covering large
Phosphates, Arsenates And Vanadates 269
areas. It is often mixed with other phosphates, with the bones and teeth of animals and with other impurities This is the well known phosphate rock or phosphonte
Localities — Crystallized apatite is so widely spread that it is useless to mention its occurrences It is mined at Kragero and near Bamle, in Norway, at various points in Ottawa County in Quebec, and in Frontenac, Lanark and Leeds Counties in Ontario, and at Mineville, New York Rock phosphate is found in extensive beds on the west side of the peninsula of Florida, in South Carolina, North Carolina, Alabama, Tennessee, Wyoming, Idaho, Utah and Arkansas A mixture of apatite and ilmemte (nelsomte), occurs as dikes in Nelson and Roanoke Counties, Virginia
Uses — The principal use of apatite and phosphate rock is in the manufacture of fertilizers The rock (or crushed apatite) is treated with H2S04 to make an acid phosphate which is soluble in water Am- monia or potash, or both, are added to the mass and the compound is sold as a superphosphate. The purest varieties are treated with H2S04 in sufficient quantity to entirely decompose them, CaSO* and HsPO* being formed The latter is drawn off and mixed with additional high- grade rock and the mixture is known as concentrated phosphate Super- phosphates are manufactured in large quantities in the United States and the concentrated phosphates in Europe Unfortunately, for the latter use the best grades of apatite or rock phosphate are required, and consequently the best grades of rock produced in the United States are exported and thus lost to American farmers
Production —The world's production of apatite and phosphate rock during 1912 was as follows*
United States 3,020,905 tons, valued at $11,675,774
Tunis 2,050,200 tons, valued at 7,500,000
Christmas Island 159459 tons, valued at 2,024,036
France 313*151 tons, valued at 1,169,400
Algeria 207,111 tons, valued at 759455
Belgium 203,1 10 tons, valued at 316,703
Other countries 65,000 tons, valued at 280,000
For the United States production of 1912 the statistics are:
Florida 2,407,000 tons, valued at $9,461,000
Tennessee 423,300 tons, valued at 1,640,500
South Carolina 131,500 tons, valued at 524,700
Other States 11,600 tons, valued at 49200
270 Descriptive Mineralogy
The total production was 3,020,905 tons, valued at $11,675,77400, of which 1,206,520 tons, valued at $8,996,45600 were exported Par- tially offsetting this, there were imported guano, apatite and other phos- phates to the value of about $2,000 ooo,
Pyromorphite (Pb4(PbCl)(PO4)3)
In composition pyromorphite is PbO, 82 2 per cent, PoOi, 15 7 per cent and Cl, 2 6 per cent, but there are usually present also CaO and
The mineral is completely isomorphous apatite Its crystals are smaller and simpler than those of apatite, but they have the same habit Their axial ratio is a c=i ' 7293 This increases to i : 7354 in varieties containing calcium
Crystals are often rounded into barrel-shaped forms, and frequently are mere skeletons Tapering groups of slender crystals in parallel growths are also common Their cleavage is parallel to the &o P(no) faces, and their fracture is feebly conchoidal. The mineral also occurs in globular, granular and fibrous masses
Pyromorphite is translucent It is brittle, has a hardness of 3 5-4 and a density of about 7 Its luster is resinous and color usually green, yellow, brown or orange Some varieties are gray or milk-white Its streak is white Its refractive indices foi yellow light are: 0614, 6=2 0494 The mineral is distinctly thermo-electric.
When heated m the closed tube pyromorphite gives a white subli- mate of lead chloride It fuses easily, coloring the flame bluish green When heated on charcoal it melts to a globule, which crystallizes on cooling and yields a coating which is yellow (PbO) near the assay and white (PbCk), at a greater distance from it. When fused with Na2COs on charcoal a globule of lead results The mineral also gives the Cl and P reactions The mineral is soluble in HNOa
Pyromorphite is recognized by its form, high specific gravity and its action when heated on charcoal
Synthesis. — Crystals have been obtained by fusing sodium phosphate with PbCk.
Occurrence— The mineral occurs principally m veins with other lead ores, especially in the zone of weathering It also exists in pseudomorphs after galena.
Localities — It is found in all lead-producing regions, especially in the upper portions of veins It occurs m particularly good specimens at Pribram, Bohemia, at Ems, m Nassau, in Cornwall, Devon, Derby-
Phosphates, Arsenates And Vanadates 271
shire and Cumberland, England, at Phoemwille, Pennsylvania, and at various other points in the Appalachian region
Vies— Pyromorphite alone possesses no commercial value, but it is mined with other compounds of lead as an ore of this metal
Munetite (Pb4(PbCl)(AsO4)3)
Mimetite, or mimetesite, resembles pyromorphite in its crystals and general appearance, and many of its properties Its color, however, is lighter and its density slightly greater It occurs in crystals, m fila- ments, and in concretionary masses and crusts Its axial ratio Is i 7315 and its refractive indices for yellow light are w=2 1443, e 2 1286
The formula for mimetite demands 74 9 per cent PbO, 23 2 per cent AS205 and 2 4 Cl Usually a portion of the lead is replaced by CaO and a portion of the As by P
Mimetite fuses more easily than pyromorphite It differs from this mineral in yielding arsenical fumes when heated on charcoal More- over, when heated in a closed tube with a fragment of charcoal it coats the walls of the tube with metallic arsenic
Occurrence and Localities — It occurs with other lead minerals in veins, usually coating them either as crusts or as a series of small crys- tals It is found at Phoenix ville, Pennsylvania, m Cornwall, England, at Johanngeorgenstadt, in Germany, at Nerchinsk, Siberia, at Lang- ban, in Sweden, and at a number of other places It is, however, not as common as the corresponding phosphorus compound
Uses — It is mined with other compounds as an ore of lead.
Vanadiaite (Pb4(PbCl)(VO4))3
Vanadmite is the most widely distributed of all the vanadium min- erals It usually occurs in small bright red prismatic crystals implanted on other minerals, or on the walls of crevices in rocks It is one of the sources of vanadium
Its theoretical composition is as follows PbO =78 7 per cent, ¥205=19 4 per cent and Cl=2 5 per cent, but phosphorus and arsenic are often also present When arsenic and vanadium are present m nearly equal quantities the mineral is known as endhckite.
Its crystals are hexagonal prisms and pyramids bounded by ooP(ioTo), oP(oooi), ooP2(u5o\ P(ioTi) and other forms, with an axial ratio i : .7122 (Fig 154). Often the crystals have hollow faces
Descriptive Mineralogy
(Fig IS5) Frequently they are grouped into pyramids like those of pyromorphite The mineral occurs also m globules and crusts
Vanadmite is brittle, has a hardness of about 3 and a specific gravity of about 7 Its fracture is conchoidal Its luster is adamantine or resinous and its color ruby red, brownish yellow or reddish brown Its streak is white or light yellow The mineral is translucent or opaque Its refractive indices for yellow light are =2354, 2 299
In the closed tube vanadimte decrepitates It fuses easily on char- coal to a black lustrous mass which is reduced on being further heated in the reducing flame to a globule of lead A white sublimate of PbCk also coats the charcoal The mineral, moreover, gives the flame test
Fig. 154
Fig 154 Fig 155
—Vanadimte Crystal with loTo (m), oP, oooi (c), P, icTi (#), and
FIG 155 — Skeleton Crystal of Vanadimte
for chlorine with copper After complete oxidation of the lead by heat- ing in the oxidizing flame on charcoal the residue gives an emerald-green bead in the reducing flame with microcosmic salt and this turns to a light yellow m the oxidizing flame The mineral is soluble m hydro- chloric acid. If to the solution a little hydrogen peroxide is added it will turn brown The addition of metallic tin to this will cause it to turn blue, green and lavender in succession, in consequence of the reduc- tion of the vanadium compounds
Vanadimte is easily distinguished from most other minerals by its color, It is distinguished from other compounds of the same color by its crystallization and by the reactions for vanadium
Occurrence — Vanadmlte occurs principally in regions of volcanic rocks It is probably a result of pneumatolytic processes
Localities —Crystals are found at Zimapan, Mexico, Wanlockhead,
Phosphates, Arsenates And Vanadates 273
England, Undenas, Sweden, in the Sierra de Cordoba, Argentine, and in the mining districts of Arizona and New Mexico
Uses — Vanadmite is an important source of vanadium, which is employed m the manufacture of certain grades of steel and bronze Its compounds are, moreover, used as pigments and mordants Most of the vanadium compounds produced in this country are obtained from other vanadium minerals, among them patromte — a mixture, of which the principal component is a sulphide (VS.*) — and carnotite (p 290), but vanadmite has been used abroad and also to a small extent in the United States
Wagnerite Group
This group, in chemical composition, is analogous to the apatite group It includes a number of phosphates and arsenates containing a fluoride radical The group is monochmc (prismatic class), with an axial ratio which is approximately 19.1 15, with 18=71° 50' None of its members are important The two most common ones are wag- nente (Mg(MgF)PO4), and tnphte (Fe Mn) ((Fe Mn)F)P04
Wagnerite occurs in massive forms and in large rough crystals, with imperfect cleavages parallel to oo P 55 (100) and oo P(no) Its crystals have an axial ratio of i 9145 i . i 5059 \vith £=71° 53' They are often very complex The mineral is bnttle Its fracture is uneven Its hardness is 5 5 and density 3 09 Its color is yellow, gray, pink or green It is vitreous, translucent and has a white streak Its refractive indices are a=i 569, £=i 570, 7 1 582 It fuses to a greenish gray glass and gives the usual reactions for fluorine and phosphoric acid It is soluble in HC1 and HNOa, and heated with HgSOi it yields hydro- fluoric acid It occurs in good crystals near Werfen, Austria, and in coarse crystals near Bamle, Norway.
Triplite is an isomorphous mixture of Fe(FeF)PO4 and Mn(MnF)P04 It usually occurs massive, but is found in a few places in rough crystals The mineral is dark brown or nearly black, is translucent to opaque, and has a yellowish gra}' or brown streak It possesses two unequal cleavages perpendicular to one another and a weakly conchoidal frac- ture Its hardness is 4-5 5 and specific gravity about 3 9 Its luster is resinous. Its intermediate refractive index is i 660
Before the blowpipe tnplite fuses easily (i 5) to a black magnetic globule It reacts for Mn, Fe, F, and PaOs It is soluble in HC1 and evolves hydrofluoric acid with H2S04 It is found in coarse granite
274 Descriptive Mineralogy
veins at Limoges, France, Helsingfors, Finland, Stoneham, Maine, and Branchville, Connecticut In all of its occurrences it appears to be pneumatolytic
Basic Phosphates And Arsenates
The basic phosphates are those in which there is more metal present than sufficient to replace the three hydrogen atoms in the normal acid, HsP04 This is due to the replacement of one or more of the hydrogen atoms by a group of atoms consisting of a metal and hydroxyl (OH) All yield water when heated in the closed tube
The principal basic phosphates are amblygonite, a source of lithium compounds, dufremte and lazidite, neither of which is of economic im- portance, and hbethemte, a copper compound which occurs in compara- tively small quantities with other copper ores, and is mined with them
Ohvenite is a basic copper arsenate corresponding to the phosphate hbethemte
Amblygonite (Li(Al(F OH))PO4)
Amblygomte is an isomorphous mixture of the two compounds (AlF)LiP04 and (AlOH)LiPO-i It is an important source of lithium
The composition of the fluorine molecule is Al20s=344 per cent, Li02=io i per cent and P20s=47 9 per cent, making a total of 105 3 per cent from which deducting 5 3 per cent (0= sF), leaves 100 Nearly always a portion of the F is replaced by OH and a part of the Li by Na The pure Na(A10H)P04 is known as fremontite, and the pure Li(A10H)PO4 as montebrmte
The analysis of a specimen from Pala, California, gave:
Pa06 AlsOs PesOs MnO MgO LiaO NaaO H8O 0-P Total
4883 3370 12 09 31 988 14 595 229*10131-96 - 100 45
The mineral forms large, ill-defined triclmic crystals (Fig 156), and compact masses with a columnar cleavage Crystals are very rare, and are poorly developed Their axial ratio is .7334 : i : 7633. The cleavage pieces often show polysynthetic twinning lamellae parallel to
The cleavage of the mineral is perfect parallel to oP(ooi) Its fracture is uneven It is brittle, has a hardness of 6 and a density of 3 03, Its color is white, gray, or a very light tint of blue, pink or yellow Its luster is vitreous, except on oP where it is pearly. ' Its
Phosphates, Arsenates And Vanadates 275
FIG 156 — Amblygoiute Crystal with ooPoo, 100 (a), oP, ooi (c), oo ]P, no (A/), °oP', no (m)y w'P's, 120
/P/J5, ioi (K)
and 2'P oo , 02 1 (e)
streak is white and it is translucent Its refractive indices for yellow light are a=i 579, /3=i 593, 7=1 597
In the closed tube at high temperature it yields water which reacts acid and corrodes glass It fuses easily to an opaque white enamel It colors the flame red with a slight fringe of green When moistened with H2S04 it tinges the flame bluish green When finely powdered it dissolves readily in H2SO4 and with difficulty in HC1
Amblygomte resembles in appearance many other minerals, especially spodumene (p 378), and some forms of bante, feldspar, dolomite, etc From spodumene it is distinguished by the phos- phorus reaction and the acid water, from the others by its easy fusibility
Occurrence — Amblygomte is found in granite and in pegmatite veins associated with other lithium compounds, tourmaline, cassitente and other minerals of pneumatolytic origin In all cases it also is probably a result of pneumatolytic action associated with the last phases of granite intrusions
Localities — The mineral occurs near Pemg, in Saxony, at Arendal, in Norway, at Montebras, France, at Hebron, Paris and Peru, Maine, at Branchville, Conn , at Pala, m California, and near Keystone, in the Black Hills, South Dakota
Uses and Production — The mineral is the pnncipal source of lithium compounds in the United States. It is used in the manufacture of LiCOa, which is employed as a medicine, in making mineral waters, in photography and in pyrotechnics
It has been mined m South Dakota and in California to the extent of a couple of thousand tons, valued perhaps at $20,000.
Dufrenite QfeaCOHJsPO*)
Dufreiute, or kraunte, is a basic iron phosphate containing 62 per cent FegOs, 27 5 per cent P20s and 10 5 per cent water It may be regarded as a normal phosphate in which one H atom of HsP04 has been replaced by the Fe(OH)2 group and two by the group Fe(OH), thus
It forms small orthorhombic crystals with a cubic habit that are rare Their axial ratio is .3734 i .4262. It usually occurs massive, in
Descriptive Mineralogy
nodules, or in fibrous radiating aggregates The same substance is belie\ ed to occur also in the colloidal condition under the name ddvauute
The color of dufremte varies from leek-green to dark green, which alters on exposure to yellow and brown It is translucent to opaque, has a light green streak and is strongly pleochroic Its hardness is 3 5-4 and specific gravity about 3 3
In the closed tube it yields water and whitens It fuses easily, color- ing the flame bluish green and yielding a magnetic globule It is sol- uble in HC1 and in dilute H2S04
It is recognized by its color and the presence in it of water, phos- phorus and iron
Localities and Origin — The mineral has been observed at several points in Europe, at Allentown, New Jersey, and in Rockbridge County, Virginia It is thought to be produced by the weathering of other fer- ruginous phosphates
LazuHte ((Mg Fe)(AlOH)2(PO4)2)
Lazulite is essentially an isomorphous mixture of the two com- pounds Mg(A10H)2(P04)2 and Fe(AlOH)2(POi)2 There is also fre- quently present m it a little calcium When the proportion of the two molecules present is as 2 . i the com- position becomes FeO 77, MgO 85, A1203 32 6, P205 4S 4 and H20=S8
The mineral occurs m blue pyram- idal crystals that are monoclimc (prismatic class), with the axial ratio 9750 i i 6483 and 0=89° 14' The predominant forms are +P(nT), FIG 157— Lazulite Crystals A with — P(lli) and— P 56 (ioi)(Flg 157-4) -P, in (p) H-P, nl (e) and P 65 , xhe angle in A if i 79° 40' Twins
ioi (/) B is the same combination twinned about oo p oo (100) with oP (ooi) the composition face
are not common Those most fre- quently found are twinned about c as the twinning axis (Fig 1576) It is found also massive and in granular aggregates
The cleavage of lazuhte is not distinct Its fracture is uneven It is brittle, has a vitreous luster, is translucent or opaque, has an azure color and a white streak Its hardness is 5 or 6 and its specific gravity about 3 i Translucent crystals are strongly pleochroic in deep blue and greenish blue tints — the former when viewed along the vertical
Phosphates, Arsenates And Vanadates 277
axis Their indices of refraction for yellow light are i 603, i 632, 7=i 639
In the closed tube lazuhte swells, whitens and yields water When heated in the blowpipe flame it whitens, falls to pieces and colors the flame bluish green The white powder moistened with Co(NOs)2 and reheated regains its blue color. When moistened with HgSC and heated in the blowpipe flame it imparts to it a green blue color It is infusible and is unacted upon by acids
Lazulite, when massive, closely resembles in appearance massive forms of some varieties of sodahte, hauymte and lazunte (p 333) The latter, however, are soluble in HC1. Moreover, none of them contains phosphorus
Occurrence — The mineral occurs in quartz veins in sandstones and slates and is usually a product of metamorphism It is sometimes, how- ever, found in serpentine rocks, with corundum, in which case it may be original
Localities — Good crystals occur at Kneglach, in Styna, at Horrs- joberg, in Sweden, and in the United States at Crowder's Mountain, North Carolina, and on Graves Mountain m Georgia,
Olivenite Group
The ohvenite group includes a number of basic copper, lead and zinc compounds of the general formula R"o(OH)R'"04 m which R" Cu, Zn, Pb and R'"=As, P, V The group is orthorhombic (bipyramidal class), with axial ratios approximating 95 . i 70 The most important members of the group are the two copper min- erals, ohvemte, Cu(CuOH) As04 and libethemte, Cu(CuOH)P04
Ohvenite occurs m fibrous, globular, lamellar, granular and earthy masses and in prismatic and acicular crystals bounded by oo P(uo), oo P 60 (100), oo P 06 (oio), P & (on) and P 56 (101) (Fig 158) Their axial ratio is 9396 i . 6726 and the angle 1 10 A 1 10= 86° 26'. Their cleavage is poor.
The mineral is some shade of green, brown, yellow or grayish white and its streak is olive-green m greenish varieties. It is transparent to opaque, is brittle, has a hardness=3, and a specific gravity =4.3. Its refractive indices for
to 158 — Ohvenite Crystal with oo Poo, zoo (a), oo p, no (m), oo Poo ,010 (6), P oo , on (e) and P 55 , 101
278 Descriptive Mineralogy
ydlow light are about i 83. Its luster is usually vitreous Fibrous vaneties are sometimes known as wood-copper
Ohvemte fuses easily (2) to a mass that appears crystalline on cooling It gives the usual reactions for EkO, Cu, and As It is soluble in acids and in ammonia
It is associated with other copper compounds in some copper ores Its ongin is secondary in all cases It occurs in the Tmtic district, Utah, and in many copper veins in Europe and in South America
Libethenite occurs in compact or globular masses and in small crystals that resemble those of ohvemte Their axial ratio is 9605 : i 7019 and no A 110=87° 40'
The mineral is bnttle Its fracture is indistinctly conchoidal Its color is dark ohve-green and its streak a lighter shade It is translucent or transparent and has a resinous luster Its hardness and sp gr =37. Its intermediate refractive index for yellow light is i 743
When heated in the closed tube it yields water and blackens It is easily fusible (2) It yields the usual reaction for Cu and P, and is sol- uble m acids and in ammonia It is distinguished from ohvemte by the reaction for phosphorus
It occurs at many of the localities for ohvemte, where, like this min- eral, it is a decomposition product of other copper compounds.
Eerderite (CaBe(OH'F)P04)
Herdente is an isomorphous mixture of the two phosphates, CaBeFP04 and CaBe(OH)P04. The latter molecule occurs in nature as hydro- kerdente, the former occurs only in mixtures The theoretical compo- sition of the fluorine (I) and bydroxyl (II) molecules and of transparent crystals from Stoneham (III), and Pans (IV), Maine, are given below
BeO CuO P205 F H20 Ins.
. . . 100
5 59 - ioo
3 70 99 67
44 ioo 51
The mineral is found only in crystals, which are monoclmic, with a : b : $=.6301 : i : .4274 and £=89° $4*. Their habit is hexagonal, pyramidal or short prismatic, elongated in the direction of a
I- Is 39
Ii. 15 53
Iii. 15 51
rv. 16 13
44 Os
53S
Phosphates, Arsenates And Vanadates 279
Herdente is colorless or light yellow, transparent or translucent Its refractive indices are i 592, /3= i 612, i 621
Its density is about 3, diminishing, as the amount of hydroxyl in- creases, to 2 952 in the pure hydroherderite
Before the blowpipe herderite first phosphoresces with an orange- yellow light, then fuses to a white enamel, colors the flame red and yields fluorine In the closed glass tube most specimens yield an acid water, which, when strongly heated, evolves fluorine that etches the glass The mineral also reacts for phosphorus with magnesium nbbon It is slowly soluble in HC1
Occurrence Origin and Uses — Herderite occurs m pegmatite dikes at Stoneham, Hebron, and other places in Maine, and at the tin mines of Ehrenfriedersdorf, Saxony, in all of these places it is apparently of pneumatolytic origin The material from Maine is used to a small extent as a gem stone
Acid Phosphates
Acid phosphates are those m which all of the hydrogen atoms of the acids have not been replaced by metals or by basic radicals Theoret- ically, they contain replaceable hydrogen atoms There are 12 or 15 minerals that are thought to belong to this class, but the composition of many of them is very obscure Most of them appear to be hydrated The only important mineral that may belong to the class is the popular gem stone, turquoise. This, according to the best analyses, contains its components in the proportions indicated by the formula CuO, 3Al2Os, 2P2Os, 9H20, which may be interpreted as (CuOH)(Al(OH)2)6H5(P04)4, which is 4(HsP(>4), in which 6 hydrogen atoms are replaced by 6Al(OH)s groups and one by the group CuOH.
Turquoise ((CuOH)(Al(OH)2)6H5(P04)4)
Turquoise is apparently a definite compound of the formula indicated above, which requires 34 12 per cent P20s, 36 84 per cent Al20a, 9 57 per cent CuO and 19 47 per cent H20 Analysis of a crystallized variety from Lynch, Campbell Co , Virginia, gave
P205 A1203 Fe203 CuO H20 Total
34 13 36 5° 2I 9 °° 20 I2 99 96
Most specimens, however, have not as simple a composition as this They are probably isomorphous mixtures of unidentified phosphates.
280 Descriptive Mineralogy
The mineral as usually found is apparently an amorphous or cryp- tocrystalline, translucent or opaque material with a wa\y lustei and a sky-blue, green or greenish gray color Material recently found at Lynch, Virginia, however, occurs in minute tnclmic crystals with an axial ratio 7910 . i 6051, \Mtha=87°o2/?/3=86° 2q', and 72° 19' Their habit is pyramidal with ooP 60(100), oop 06(010), oo 'P(iTo), ooP'(no) and POO (oil)
The fracture of turquoise is conchoidal. It has a hardness of 5-6 and a specific gravity between 261 and 2 89 It is brittle, and has cleav- ages in two directions. The determined refractive indices of the Vir- ginia crystals are: a=i.6i, 1.65
In the closed tube the mineral decrepitates, yields water and turns black or brown It is infusible, but it assumes a glassy appearance when heated before the blowpipe and colors the flame green. When moistened with HC1 and again heated the flame is tinged with the azure blue of copper chloride The mineral reacts for copper and phosphoric acid Some specimens dissolve m HC1, but the crystallized material from Vir- ginia is insoluble until after it is strongly ignited It partly dissolves in KOH, with the production of a brown residue of a copper compound
Occurrence — Turquoise occurs in thin veins cutting through certain decomposed volcanic rocks and other rocks in contact with them, and in grains disseminated through them, in stalactites, globular masses and crusts It is probably an alteration product of other com- pounds
Localities — Turquoise is found in narrow veins and irregular masses in the brecciated portions of acid volcanic rocks and the surrounding clay slates, near Nish&pur, in Persia, in the Megara Valley, Sinai, and near Samarkand, in Turkestan In all these places the mineral is of gem quality and until recently nearly all the gem turquoise came from them Within late years gem turquoise has been discovered in the Cenllo Moun- tains, near Santa Fe, New Mexico, where it has been mined in consid- erable quantity The locality is the site of an ancient mine which was worked by the Mexicans It is also found and mined in the Burro Mountains, Grant County, in the same State, near Millers, and at other points in Nevada and near Mineral Park, Mohave County, Arizona, where also the ancient Mexicans once had mines At La Jara, Conejos County, Colorado, old mines have likewise been opened up and are now yielding gem material
Uses —The only use of turquoise is as a gem stone Though much of the American mineral is pale or green, some of it is of as fine color as the Oriental stone A favorite method of using the stone is in its
Phosphates, Arsenates And Vanadates 281
matrix Small pieces of the rock with its included turquoise are pol- ished and sold under the name of turquoise matrix
Production — The total value of the turquoise and turquoise matrix produced in the United States during 1911 was $44,751 This weighed about 4,363 pounds In several previous years the production reached about $150,000, but in 1912 it was valued at only $10,140
HYDROUS PHOSPHATES AND ARSENATES HYDRATED NORMAL PHOSPHATES AND ARSENATES
Of the hydrous salts of orthophosphonc and orthoarsemc acids there are two which are of some importance because they are fairly common, a third which is utilized in jewelry, and a fourth that is important as an indicator of the presence of an ore of cobalt. The first two are wwanite and scorodtte, a phosphate and an arsenate of iron, the third is vanszite, an aluminium phosphate, and the fourth is erytknte, an arsenate of cobalt A dimorph of vanscite, known as lucmite, is rare All give water in the closed tube and yield phosphine when fused with magne- sium and moistened with water
Vivianite Group
The only important group of the hydrated orthophosphates and orthoarsenates is that of which viviamte and erythnte are members. The general formula of the group is R"3(R'"04)2 8H20 in which R" =Fe, Co Ni, Zn and Mg, and R'"=P or As Although some members have not been found in measurable crystals, crystals of all have been made in the laboratory, so that there is little doubt of their isomorphism. All are monochmc prismatic with axial ratios of about 75 i : 70 and ft about 74° The group is as follows
Bobente, Mg3(P04)2 8H20 ErytMte, Co3(As04)2 8H20
Horneste, Mg3(As04)2 8H20 Annabcrgde, Nm(As04)2 8H20
Vtwamte, Fe3(P04)2 8H20 Cabrente, (Ni Mg)3(As04)2 8H2O
Symplestte, Fe3(As04)2 8H20 Kottigite, Zn3(As04)2 8H20
Only vivianite, erythnte and annabergite are described
Vivianite (Fe3(P04)2 8H2O)
Vivianite is a common phosphate of iron It occurs not only in dis- tinct crystals but also as bluish green stains on other minerals, and as an invisible constituent of certain iron ores, thereby diminishing their value.
282 Descriptive Mineralogy
Its formula indicates the presence of 43 per cent FeO, 28 3 per cent P20s and 28 7 per cent BkO
Viviamte crystals are monoclmic (prismatic class), usually with a prismatic habit Their axial ratio is 7498 . i 7015, and £=75° 34' The principal forms observed on them are oo P 56 (100), oo P ob (oio), ooP(no), °oP3(3io), P&O(IOI), P(III) and oP(ooi) The angle uoAi"io=7i° 58' The mineral also occurs in stellate groups, in glob- ular, fibrous and earthy masses and as crusts coating other compounds
Its cleavage is perfect parallel to oo P (oio) It is flexible in thin splinters and sectile. The fresh, pure mineral is colorless and trans- parent, but specimens usually seen are more or less oxidized and have a blue or green color It has a vitreous to pearly luster Its streak is white or bluish, changing to indigo-blue or brown on exposure to the air Its pleochroism is strong in blue and pale yellow tints Its hardness is i 5-2 and density about 2 6. Its refractive indices for yellow light are a=i 5818, jS-i 6012, 7-1 6360
In the closed tube viviamte whitens, exfoliates and yields water at a low temperature It fuses easily (2), tingemg the flame bluish green Its fusion temperature is 1114°. The fused mass forms a grayish black magnetic globule. It gives the reaction for iron, and is soluble in HC1
The mineral is easily recognized by its softness, easy fusibility and by yielding the test for phosphorus.
Synthesis — Crystals have been made by heating iron phosphate with a great excess of sodium phosphate for eight days
Occurrence and Origin. — Vivianite occurs in veins of copper, tin and gold ores; disseminated through peat, clay, and limomtc, coating the walls of clefts in feldspars and other minerals of certain igneous rocks, and partially filling cavities in fossils and partly fossilized bones It is usually the result of the decomposition of other minerals
Localities, — Crystals are found at several points m Cornwall, Eng- land, at the gold mines at Verespatak, in Transylvania, at Allentown, Monmouth County, New Jersey, and at many other places The earthy variety occurs at Allentown, Mullica Hill and other points in New Jer- sey, in Stafford County, Virginia, and in swamp deposits at many places It is abundant in limomte at Vaudreuil, in Quebec, and in bog iron ores elsewhere.
Erythrite (Co3(As04)2 8H20)
Erythnte, or cobalt bloom, isinot a common mineral, but, because of its beauty and the fact that it is the usual alteration product of cobalt ores, it deserves to be described
Phosphates, Arsenates And Vanadates 283
In composition erythnte is 37 5 per cent CoO, 38 4 per cent As205, and 24 i per cent H20 It usually, ho\\e\er, contains some iron, nickel and calcium
The mineral is isomorphous with vivianite Its crystals are mono- climc and prismatic or acicular and their axial ratio is 7037 i 7356 and jS=74° 51' The are stnated vertically Erythrite occurs in all the forms in which vivianite is found Its crystals are usually bounded by ooP 03(010), ooP(no), oop 66(100), +Po6(Toi) and
The cleavage of erythnte is perfect parallel to oo P ob (oio) It is transparent or translucent, has a gray, crimson or peach-red color, and a white or pink streak Its hardness varies between i 5 and 2 5 and its density is 295 Its luster is pearly on oo Poo (oio) and vitreous on other faces It is flexible and sectile. Its refractive indices for yellow light are a— i 6263, i 6614, i 6986
In the closed tube ery thrite turns blue and yields water at a low tem- perature At a high temperature it yields As20<j, which condenses in the cold portion of the tube as a dark sublimate It fises at 2, and tinges the flame pale blue On charcoal it fuses, yields arsenic fumes and a gray globule which colors the borax bead a deep blue The mineral is soluble in HC1, giving rise to a pink solution, which, upon evaporation to drynesSj gives a blue stain
It is easily recognized by its color and the cobalt reaction. It is readily distinguished from pink tounna\ne (p 434), by its hardness and easy fusibility
Synthesis — Crystals have been obtained by carefully mixing to- gether warm solutions of CoSO-i and HNa2As04 7HsO
Occurrence — Erythnte occurs in the upper portions of veins con- taining cobalt minerals, being formed by their weathering
Localities — Tt occurs as scales and crystals at Schneeberg, Saxony, and as crystals at Modum, Norway. It is found, also, at Lovelock's Station, Nevada, at several points m California and in large quantities at Cobalt, Ontario.
Annabergite (Ni3(As04)2-8H20)
Annabergite, or nickel bloom, is isomorphous with erythnte It occurs massive, disseminated m tiny grains through certain rocks, as crusts and stains m globular and earthy masses, and in fibrous crystals, the axial ratios of which are not known.
The mineral is apple-green in color, and is translucent or opaque.
284 Descriptive Mineralogy
Its streak is light green Its luster is vitreous, its hardness, i 5-2 5 and sp gr
Before the blowpipe it melts to a gray globule and gives the arsenic odor In the closed glass tube it blackens and yields water In the beads it gives the usual reactions for Ni The mineral dissolves easily in acids
Synthesis —Crystals have been produced by the method employed in the synthesis of erythnte, using NiSO-i, instead of CoSC>4
Occurrence — It is found as a common alteration product of nickel- bearing minerals, in the oxidized portions of veins
Localities — Its best known occurrences are m Allemont, Dauphme, Annaberg and Schneeberg, Saxony, Cobalt, Ontario, and mines in Colorado and Nevada.
Variscite (A1P04 2H20)
Vanscite is a bright green mineral that has recently come into use as a gem material. It is apparently an aluminium phosphate with a theoretical composition as follows 449 per cent P20r>, 32 3 per cent AloOa and 228 per cent HO A specimen of crystallized material from Lucm, Utah, gave the following analysis
P205 A1203 Fe203 Cr03 V203 H20 Total
44 73 32 40 06 18 32 22 68 100 37
Recent investigations indicate that the compound A1P04 2H20 is dimorphous Both forms are orthorhombic but one, vanscite, has the properties described under this heading The other, lucinite, is associ- ated with vanscite, near Lucm, Utah. It, however, occurs in crystals that are octahedral in habit, rather than tabular, and that have an axial ratio of 8729 i 9788 In other respects lucimte is very much like variscite
An amorphous variety of the same substance is also known It occurs as a white, pale brown or pale blue earthy mass with a sp gr of 2.135 It differs from the crystalline varieties in being completely soluble in warm concentrated H2S04
The crystals of vanscite are orthorhombic and are bounded by co P 66 (oio), oo P(no) and £P oo (012), and in a few cases oo P 60 (too) Their axial ratio is 8944 .1:1 0919 Nearly all crystals are tabular parallel to oo P 56 (oio) Twins are common, with 60 (102) the twinning plane Crystals are comparatively rare, the mineral occur- ring usually in fibrous or finely granular masses and as incrustations
Phosphates, Arsenates And Vanadates 285
Vanscite vanes in color from a pale to a bright green It is weakly pleochroic, has a vitreous luster, a hardness of about 4 and a density of 2 54 Its refractive indices for yellow light are a=i 546, /3=i 556, r=i 578
Before the blowpipe the mineral is infusible It, however, whitens and colors the flame deep bluish green It )ields water in the closed tube, and with the loss of its water, it changes color from green to lavender The same change in color takes place gradually at temper- atures between iio°-i6o° When heated with Co(N03)2, it turns blue and when fused with magnesium ribbon it gives the test for phosphorus It forms a yellowish green glass with borax or microcosmic salt. The mineral is insoluble in acids before heating
Vanscite resembles m some respects certain varieties of turquoise and wwuellite (p 287) It is distinguished from turquoise by the absence of copper and from wavellite by its insolubility in acids
Occurrence — The mineral occurs as a cement in a brecciated, cherty limestone and a brecciated rhyolite, as nodules m the cherty portions of the breccias and also as veins traversing these rocks It is also found as nests in weathered pegmatites The crystals occur as coarsely granular, loosely coherent masses in more compact granular masses
Localities — Vanscite occurs at Messbadi, Sa\ony, in Montgomery County, Arkansas, near Lucm, Utah, and at a number of other places in Tooele and Washington Counties in this State, in Esmeralda County, Nevada, and m Montgomery County, Arkansas The colloidal vanety occurs as concretions in slates at Brandberg, near Leoben, Austria
Uses — The mixture of vanscite and rock is cut, and employed as sets in necklaces, belt pins, etc , under the names " utahlite " and " amatrice," but because of the softness of the vanscite it cannot be used with success for all the purposes for which turquoise matrix is used
Production — The production of the material in the United States during 1911 was 540 Ib , valued at $5,750 In the previous year 5,377 Ib were reported as having been sold for $26,125, In I9I2> the amount marketed was valued at $8,150.
Skorodite
Skorodite is more common than viviamte It occurs in globular and earthy masses, as incrustations, and in crystals of a green or brown color The globular forms are colloidal
Its formula indicates Fe203=346 per cent, Asa03=498 Per cent
286 Descriptive Mineralogy
and HoO= 15 6 per cent An incrustation on the deposits of the Joseph's Coat Spring, Yellowstone National Park, consisted of
As2O5 Fe2O3 H2O SiO2 SO3 Total
46 48 33 29 I5 5° 4 35 84 100 46
Its crystallization is orthorhombic (bipyramidal class), with a b . c — 8658 . i 9541. The crystals, which are commonly bounded by oo P 60(100), oo P 06(010), ooPa(i2o), ooP(uo), P(III) and -2-P(ii2), are either prismatic or octa- hedral m habit (Fig 159) The angle niAiTi 65° 20' Their cleavage is imperfect, parallel to ooP(no)
The mineral is brittle It has a vitreous luster, a leek-green or liver-brown color and a white streak. It is translucent and has an uneven frac- ture Its hardness is 3 5-4 and density about 3 3 FIG 159 —Skorodite The colloidal phases are somewhat softer than the Crysta wit oo co , crysta}}me phases 100 (a) oo P 2, 1 20
(d) and P m (p) In "the closed tube skorodite turns yellow and
' yields water It fuses easily, coloring the flame
bluish. On charcoal it yields white arsenical fumes and gives a black
porous, magnetic button It is soluble in HC1, forming a brown solution
It is distinguished from wviamte by the arsenic test, and from dufren-
%te by its streak and reaction in the closed tube
Synthesis — Skorodite crystals have been made by heating metallic iron with concentrated arsenic acid solution at I4o0~i$o0
Occurrence. — Skorodite is frequently associated with arsenopynte, in the oxidized portions of veins containing iron minerals It is found also in a few places as incrustations deposited by hot springs,
Localities — It occurs m fine crystals at Nerchinsk, Siberia; at Loelling, m Cannthia, near Edenville, New York, in the Tmtic dis- trict, Utah, and as an incrustation on the siliceous sinter of the geysers in Yellowstone Park.
Hydrated Basic Phosphates And Arsenates
The hydrated basic phosphates and arsenates are rather more nu- merous than the hydrated normal compounds, but most of them are rare One, waveltite, however, is a handsome mineral that is fairly common. Another, pharmacosiderite, an iron arsenate, is known to occur at a number of places The uramte group also belongs here Its members
Phosphates, Arsenates And Vanadates 287
are comparatively rare, but, because of the presence of uranium in them, they are of considerable interest
Wavellite ((A1(OH F)3)(PO4)2 5H2O)
Wavellite rarely occurs in crystals It is usually in acicular aggre- gates that are either globular or radiating (Fig 160) The few crystals that have been seen are orthorhombic (bipyramidal class), with an axial ratio of 5573 i . 4057
Its composition varies widely, and frequently a fairly large portion of the OH is replaced by F, and a portion of the Al by Fe
The mineral is vitreous in luster and white, green, yellow, brown or black in color Its streak is white It is brittle and translucent, m-
FIG 1 60 — Radiate Wavellite on a Rock Surface
fusible and insoluble m acids Its hardness is 3 5 and its density 2.41. Its intermediate refractive index for yellow light is i 526.
Heated m a dosed glass tube, wavelhte yields water, the last traces of which react acid and often etch the glass In the blowpipe flame the mineral swells up and breaks into tiny infusible fragments, at the same time tingeing the flame green. The mineral is soluble in HC1 and H2SO4. When heated with HaS04 many specimens yield hydrofluoric acid When heated on charcoal and moistened with Co(NOs)2 and reheated, the mineral turns blue.
Wavellite is distinguished from turquoise, which it sometimes resembles, by its action in the blowpipe flame, by its inferior hardness and its manner of occurrence
Occurrence — Wavellite occurs as radiating bundles on the walls of
288 Descriptive Mineralogy
cracks in various rocks and as globular masses filling ore veins and the spaces between the fragments of breccias It is probably m all cases the result of weathering
Localities —It is found at a great number of places, especially at Zbirow, in Bohemia, at Mmas Geraes, Brazil, at Magnet Cove, Arkan- sas, and in the slate quarries in York County, Penn.
Pharmacosidente ((FeOH)3(AsO4)2 5H2O)
Pharmacosiderite is a hydrated ferric arsenate, the composition of which is not firmly established It usually occurs m small isometric crystals (hextetrahedral class), that are commonly combinations of
ooQoo(ioo) and — (in) It is also sometimes found in granular
masses Its cleavage is parallel to oo 0 °o (100)
The mineral is green, dark brown or yellow. Its streak is a pale shade of the same color It has an adamantine luster and is translucent. Its hardness 25 and sp gr It is sectile and pyroelectnc Its refractive mde\, 676
Pharmacosiderite reacts like skorodite before the blowpipe and with reagents
The mineral occurs m the oxidized portions of 01 c ems, in Cornwall, England, at Schneeberg, Saxony, near SchemmU, Hungai} , and in the Tintic district, Utah.
Uranite Group
The uramtes are a group of phosphates, arsenates and vanadates containing uranium m the form of the radical uranyl (UOs) which is bivalent The members of the group are either tetragonal, or ortho- rhombic with a tetragonal habit They all contain eight molecules of water of crystallization Only three members of the group are of sufficient interest to be discussed here These are the hydrated cop- per and calcium uranyl phosphates, torbermte and aittumte and the potassium uranyl vanadate, carnotite
The entire group so far as its members have been identified is as follows.
Awlumte Ca(U02)2(P04)2 8H20 Orthorhombic
Uranospwite Ca(U02}2(As04)2 SBfcO Orthorhombic
Torb&rmte Cu(U02)2(P04)2 8H20 Tetragonal
Zeunente Cu(U02)2(As04)2 8H20 Tetragonal
Uranocirate Ba(U02)2(P04)2 8H20 Orthorhombic
Camohte (Ca
Phosphates, Arsenates And Vanadates 289
The uramtes are of interest because of their content of uranium, an element which is genetically related to radium
Autunite (CaCUCbMPO 8H2O)
Autunite occurs in thin tabular crystals with a distinctly tetragonal habit, and in foliated and micaceous masses
The percentage composition corresponding to the above formula is 6 i per cent CaO, 62.7 per cent UOs, 15 5 per cent PsOs and 15 7 per cent H2O
Its crystals are orthorhombic (bipjrraimdal class), with an axial ratio, p875 : i 28517, thus possessing interfacial angles that closely approach those of torbermte. Its crystals are bounded by oP(ooi), P a (101), P 06 (on), and several less prominent planes Their cleav- age is very perfect and the cleavage lamellae are brittle The luster is pearly on the base and vitreous on other surfaces.
The mineral is lemon-yellow or sulphur-yellow in color, and its streak is yellow It is transparent to translucent. Its hardness is 2-2 5 and its specific gravity about 3 2. Its refractive indices for yellow light are.
i 553,0=1 S7S>7=i577
The mineral reacts like torbermte before the blowpipe and with acids, except that it shows none of the tests for copper. It is recognized by its color, streak and specific gravity
Occurrence — Autunite occurs m pegmatite veins and on the walls of cracks in rocks near igneous intrusions, especially in association with other uranium compounds, of which it is a decomposition product.
Localities. — It has been found at Johanngeorgenstadt, Germany, at Middletown and Branchville, Conn , in the mica mines of Mitchell County, North Carolina, and coating cracks in gneiss at Baltimore, Md
Torbernite (CuCUOsCPO -8H20)
Torbermte occurs in small square tables, that may be very thin or moderately thick, and in foliated and micaceous masses.
The pure mineral contains 612 per cent UOs, 8 4 per cent Cu, 15 i per cent P20s and 15.3 per cent H2<D, but frequently a part of the P is replaced by As
Its crystals are tetragonal (ditetragonal bipyramidal class), with a i . 2 9361 They are extremely simple, their predominating forms being oP(ooi) and POD (101). Less prominent are ooPoo (100), sPoo(2oi) and ooP(no) Their cleavage is perfect parallel to oP The cleavage lamellae may be almost as thin as those of the micas but they are brittle
290 Descriptive Mineralogy
The mineral is bright green in emerald, grass or apple shades, has a lighter green streak, is translucent or transparent, and has a hardness of 2 25 and a specific gravity of about 3 5 Its luster is pearly on the basal plane but nearly vitreous on other burfaces It is strongly pleo- chroic in green and blue.
Torbermte gives reactions for Cu and P and yields water in the closed tube The bead reactions for uranium are masked by those of copper The mineral is soluble in HN03
The mineral is easily recognized by its color and other physical properties
Occurrence. — Torbermte is occasionally found as a coating on the walls of crevices in rocks It occurs in Cornwall, England, at Schee- berg, Saxony, at Joachimsthal, Bohemia, and at most places where other uranium minerals exist It is probably in all cases a weathering product.
Carnotite ((Ca KsXTTCMVO xHaO)
Carnotite, like the other uramtes described, is extremely complex in composition It may be an impure potassium uranyl vanadate, or a mixture of several vanadates in which the potassium uranyl compound is the most prominent The formula given above indicates its com- position as well as any simple formula that has been proposed A specimen from La Sal Creek, Colorado, shows the mineral to be essen- tially as follows '
UOs CaO BaO K20 H20 at 105° H20 above 105° 18 05 54 oo i 86 i 86 5 3 16 2 21
though there are present in the specimen analyzed, or in other specimens from the same locality, also As203, P2O5, Si02, Ti02, C02, S03, Mo03, Cr203, Fe203, A1203, PbO, CuO, SrO, MgO, Li20 and Na20, and there are reported in them also small quantities of radium Radiographs taken with the aid of carnotite have been published, which are almost as clear as those taken with pitchblende The complete analysis of a specimen from the Copper Prince Claim, Montrose Co , Colo , gave:
CuO
Also Na20=
As205
CaO
TiOa=.
P205
BaO
10, C02=
U03 MoOg Fe203 52 25 23 i 77
K20 H20- H20+ 6 73 2 59 3 06
33, S03=.i2, CrOs=tr,
A1203
Ins
MgO=
PbO
Total 20 and
Phosphates, Arsenates And Vanadates 291
The mineral has been found only in tiny crystalline grams, so that its physical properties are not well known It is bright yellow in color, and is completely soluble in HNOs If to the nitric acid solution hydro- gen peroxide be added a brown color will appear Or if the solution is filtered, made alkaline by ammonia and through it is passed H2S, a garnet color will develop If the mineral be moistened by a drop of concentrated HC1, a rich brown color will result The addition of a drop or two of water will change the color to light green or make it disappear
Occurrence — Carnotite occurs as a yellow crystalline powder, some of which seems to consist of minute crystals with an hexagonal habit, in the interstices between the grains in sandstones and conglomer- ates, as nodules or lumps in these rocks, and as coatings on the walls of cracks in pebbles in the conglomerates and on pieces of silicified wood embedded in the sandstones. It is limited to very shallow depths and is apparently a deposit from ground water.
Localities — Its principal known occurrences are in Montrose, San Miguel, Mesa and Dolores Counties in southwestern Colorado, especially in Paradox Valley, and in adjoining portions of New Mexico and Utah, and in Rio Blanco and Routt Counties in the northwestern portion of Colorado. At all these places there are large quantities of the impreg- nated rock but it contains on the average only about i 5 per cent to 2 per cent of UsOg. The mineral has also been described from Mt Pisgah, Mauch Chunk, Pennsylvania, and from Radium Hill, South Australia
Uses. — The mineral is one of the main sources of radium and uranium and is one of the principal sources of vanadium. Although it contains a notable quantity of uranium, carnotite has little value except as an ore of radium and vanadium, because of the few uses to which uranium is put. This metal is used to some extent in making steel alloys and in the manufacture of iridescent glazes and glass Its compounds are used in certain chemical determinations, as medicines, in photography, as por- celain paint, and as a dye in calico printing. The uses of vanadium have been referred to on p 273
The principal value of carnotite depends upon its content of radium, which in the form of the chloride is valued at about $40,000 per gram or $1,500,000 per oz The importance of radium as a therapeutic agent has not been established, but that its use is wonderfully helpful in many diseases is beyond question Without doubt in the near future carno- tite will become the principal source of radium in the world Practically the only other source is the pitchblende (p 297), of Gilpin, Colorado, Cornwall, England and Joachimsthal, Austria.
292 Descriptive Mineralogy
Production — Carnotite has been mined in San Miguel and Montrose Counties, Colorado, and at several points in eastern Utah, but mainly for the vanadium it contains At present it is being utilized as a source of radium From Colorado 8,400 tons of vanadium ore, with a value of $302,000, were shipped in 1911 and from New Mexico and Utah about 70 tons, valued at $3,500 Some of this, however, was vanadmite Most of it was exported and used as a source of vanadium However, the uranium content of the carnotite mined was about i r tons of the metal During 1912 ore containing 26 tons of uranium o\ide and 6 7 grams of radium was produced This would have yielded n 43 grams of radium bromide, valued at $52,800 The present price of standard carnotite carrying at least 2 per cent UgOg and 5 per cent VOs, is at the rate of $i 25 per Ib for the former and thirty cents for the latter In 1914 the selling price of 4,294 tons of carnotite ore containing 87 tons of UsOg was $103 per ton At the present time nothing is paid for the radium content of the ore, though this is its most valuable component One ton of ore containing i per cent of UaOg carries 2 566 milligrams of radium The imports of uranium compounds during 191*2 were valued at $14,357-
Hydrated Acid Phosphates And Arsenates
A number of hydrated acid phosphates and arsenates are known to constitute an isomorphous group, but only a few of them occur as minerals. Brushite is an acid calcium phosphate and pfwrmacofate is the corresponding arsenate Both crystallize in the monoclimc system (prismatic class) Neither is common
Pharmacohte (HCaAs04 2H20) occurs principally in silky fibers, in botryoidal and stalactic masses and rarely in crystals with an axial ratio .6236 ' i : 3548 and 18=83° 13'. Their cleavage is perfect par- allel to oo P ob (oio) The mineral is white or gray, tinged with red Its streak is white It is translucent or opaque Its luster is vitreous, except on oo P & (oio) where it is slightly pearly Thin laminae are flexible Its hardness is 2-2 5 and density 2 7 Its refractive indices for yellow light are. 01=1.5825, ]8=i 5891, 7=1 5937
Before the blowpipe pharmacohte swells up and melts to a white enamel. The mineral gives the usual reactions for As, EfeO and Ca It usually occurs in the weathered zone of arsenical ores of Fe, Ag and Co, at Andreasberg, Harz; Joachimsthal, Bohemia, and elsewhere.
Chapter Xv The Columbates, Tantalates \Nd Uranates
THE rare metah, columbium and tantalum, exist in a few silicates, but their principal occurrences are as columbates and tantalates which are salts of columbium and tantalum acids, analogous to the various acids of sulphur The commonest compounds are salts of the meta- acids EfeQteOo and H2Ta20e, the relations of which, to the normal acids, are indicated by the equation 2HsCb04— 2H20=H2Cb206 Other im- portant minerals are derivatives of the pyroacids corresponding to HiCtaOr, or 2HsCb04— EkO The best known ortho salt is ferguson- tte, YCb04, but it is rare
All the columbates yield a blue solution when partially decomposed in EfeSQi and boiled with HC1 and metallic tin The tantalates when fused with KHSO* and treated with dilute HC1 give a yellow solution and a heavy white precipitate, which, on treatment with metallic zinc or tin, assumes a deep blue color When diluted with water the blue color of the tantalate solution disappears, whole that of the columbate solution remains
The uranates are salts of uramc acid, HsUtX. The only mineral known that may be a uranate is urarnn/Ue9 and the composition of this is doubtful.
Columbite (CFe-Mn)Nb2O6) and Tantalite ((Fe-Mn)Ta2O6)
These two minerals are isomorphous mixtures of iron and manganese columbates and tantalates The name columbite is applied to the mix- ture that is composed mainly of the columbates, and tantalite to that which is principally a mixture of tantalates When the tantalite is composed almost exclusively of the manganese molecule, it is known as manganotantalte Tin and tungsten are frequently found in both min- erals
Their crystals are orthorhombic, with a : b . c— 8285 : i : 8898 for the nearly pure columbium compound, and 8304 : i : .8732 for the nearly pure tantalum compound Both form short prismatic crystals containing many faces, among the most prominent being the three pinacoids, various prisms, notably °o P(no), oo Pjfoo) and oo P6(i6o),
Descriptive Mineralogy
and the domes 2? 56 (201) and 06 (012) (Fig 161) The most promi- nent pyramids are P(in) and P3(i33). Twins are not uncommon, with 2P66 (201) the twinning plane The angle noAiIo for colum- bite=79° 17'
Both minerals are usually opaque, black and lustrous, and occasion- ally iridescent, though, in some instances, they are translucent and broun Their streak is dark red or black Their cleavage is distinct parallel to oo P 60 (100), fracture uneven or conchoidal, their hardness
6 and their specific gravity between 5 3 and 73, in- creasing with the propor- tion of the tantalum mole- cules present They are both infusible before the blowpipe Some specimens exhibit weak radioactivity When columbite is de- composed by fusion with KOH and dissolved in HC1
and BkSO-i, the solution turns blue Qn thfi addltlon
USbdllC 1C The mm-
eral 1S also partially decom- posed when evaporated to dryness with EfeSCU, forming a white compound that changes to yellow When this residue is boiled with HC1 and metallic zinc a blue solution results The mineral also gives reactions for iron and manganese.
Tantalite is decomposed upon fusion with KHSQ* in a platinum spoon, or on foil. This when heated with dilute HCl yields a yellow solution and a heavy white powder Upon addition of metallic zinc, a blue color results and this disappears on dilution with water In the microcosmic salt bead tantalite dissolves slowly, giving reactions for iron and manganese When treated with tin on charcoal the bead turns green
The two minerals may easily be confused with black fourmahne (p. 434), tlmemte (p 462) and wolframite From tourmaline, they are distinguished by crystallization, high specific gravity and luster, from wolframite by their less perfect deavage and by the reaction with aqua regia (see p 259), from ilmenite by the test for titanium
Occurrence, Ongm and Localities.— Both minerals occur in veins of coarse granite and probably have a pneumatolytic origin
FIG i6i.-Columbite Crystals with
(a). ooPoo,oio (6), oop, no (f), °oP2, 210 Ml 730 (d), oopo (,), 55, I03
P, in W and PI 133 M
Columbates, Tantalates And Uranates 295
Columbite is found in granite \erns at Bodenmais, Bavaria, Tam- mela, in Finland, near Limoges, France, with tantahte, near Miask, in the Ilmen Mountains, Russia, with samarskite, and at Ivigtut, m Greenland In the United States it is found at Standish and Stone- ham, m Maine, at Acworth, in New Hampshire, at Haddam, in Con- necticut, at Amelia Court House, Virginia, with samarskite in the mica mines in Mitchell County, North Carolina, m the Black Hills, South Dakota, and at a number of other points in New England and the Far West
Tantahte is found at many of the localities for columbite and also at several other places in Finland, near Falun, in Sweden, in Yancy County, North Carolina, and m Coosa County, Alabama
Uses — At the present time columbium and its compounds have no commercial uses Tantalum, however, is employed in the manufacture of filaments for certain types of incandescent lamps Since, howe\er, about 20,000 filaments may be made from a single pound of the metal the market for tantalum ores is very limited
Samarskite and Yttrotantalite
These two minerals may be regarded as isomorphous mixtures of salts of pyrocolumbic and pyrotantalic acids, in which the bases are yttrium, iron, calcium and uranyl.
Samarskite, according to this view, is approximately
Y2(Ca Fe U02)3(Nb207)3
and yttrotantalite the corresponding tantalate Yttrium and iron are the principal bases, but there are also often present erbium, cerium, tungsten and tin
Analyses made by Rammelsberg and quoted by Dana give some idea of the complexity of the compounds:
Density
Ta206 Nb205 W03
Sn02 Ti02* Y203
Er20a
I 5 425
12 32 2 36
Ii- 5 839
56 6 10
Iii 5 672
i 08 8 80
Ce203t
U02
FeO
CaO
H2O
Total
I 2 22
Ii. 2 37
too 93
Hi 4 33
14 3°
I Fromltterb;
y, Sweden
II From North Carolina
HI From Miask
Russia.
Including SiO*, f Including Di20s and LaOs
296 Descriptive Mineralogy
The first of these three minerals has been called yttrotantahte and the other two samarslute If the first is weathered, as seems probable from the presence of over SL\ per cent of water, the three may constitute members of an isomorphous series with the third representing the nearly pure columbate (sanurskite), the first a compound in which the tantalate molecule is in excess (yttrotantahte), and the second an intermediate compound which contains both the tantalum and columbmm molecules, with the latter predominating
With more accurate analyses the great complexity of these compounds becomes even more apparent Hillebrand has given the following report of his analysis of a samarskite from Devil's Head Mountain, near Pike's Peak, Colorado, which shows the futility of attempting to represent its composition by a chemical formula-
Pitch-black Black Weathered
Variety Variety Variety
Ta20fi 27 03 28 ii 19 34
CbaOs 27 77 26 16 27 56
W03 2 25 2 08 5 51
SnO2 95 i 09 82
Zr02 2 29 2 60 3 10*
U02 4 02 4 22
U03 6 20
Th02 3 64 3 60 3 19
Ce203 54 49 4i
(La,Di)203 I 80 2 12 i 44
Er20s 10 71 10 70 9 82
Y203 6 41 5 96 5 64
Fe203 8 77 8 72 8 90
FeO 32 35 39f
MnO 78 75
ZnO 05 07 / 77
PbO 72 80 i 07
CaO 27 33 i 6 1 MgO „
(Na,Li)20 24 17 I
H20.. i 58 i 30 3 94
f O
Columbates, Tantalates And Uranates 297
Poo,ioi(e), 3P3> 231 W
Both samarskite and yttrotantahte are orthorhombic, with an axial ratio for samarskite of 5456 : i : 5178, and for yttrotantahte, 5411 i . i 1330. They, however, more commonly occur massive and in flattened grams embedded in rocks Their crystals are prismatic in the direction of the c or the b a\is Their most prominent forms are oo P 56 (100), oo P 66 (oio) and P 65 (101) (Fig 162) Less prominent but fairly common are *>P2(i2o), ooP(no), P(in) and The angle noAiTo for samarskite is 57° 14' and for yttrotantahte 56° 50'
The cleavage of both minerals is indistinct parallel to oo P 06 (oio) Their fracture is conchoidal Both are brittle The hardness of samarskite is 5-6, its density about 5 7, its luster vitreous, its color velvety black and its streak reddish brown Yttrotantahte is a little softer (5-5 5) Its specific gravity is 5 5~5 9, its luster submetallic to vitreous, its color black, FIG 162 — SamarshteCiys- brown, or yellow, and its streak gray to color- fed oop 55 , 100 (a), less Samarskite is opaque and yttrotantahte °°p55' OI° JW> °°p opaque or translucent
The reactions of the minerals vary with their composition They always yield the blue solution test for tantalum or columbium, and most specimens react for Mn, Fe, Ti and U The reaction for uranium is an emerald green bead with microcosmic salt in both reducing and oxidizing flame.
They are distinguished from columbite and t&ntahte by the form of their crystals.
Occurrence — The two minerals, like columbite and tantahte, are found principally in pegmatite veins and in many of the same localities Yttrotantahte occurs mainly at Ytterby and near Falun, in Sweden, and samarskite, near Miask in the Ilmen Mountains, Russia, In the United States the last-named mineral is sometimes found in large masses in the mica pegmatites of Mitchell County, North Carolina.
Uses — Neither mineral is at present of any commercial value. They are, however, extremely interesting as the source of many of the rare elements, and, especially, as a possible source of radium and closely related substances.
Urardnite
Uramnite, or pitchblende, like the other compounds containing the element uranium, is of doubtful composition. It contains so many
298 Descriptive Mineralogy
different components that a correct conception of its character is almost impossible to grasp The mineral is particularly interesting because it always contains a trace of radium, of which it is an important com- mercial source at the present time
Analyses of crystallized material (I) from Branchville, Conn, and from Annerod (II), Norway gave the following results
U03 U02 ThO2 PbO Fe2O3 CaO H2O Pie Insol
I. 21 54 64 72 6 93 4 34 28 22 67 Und. 14
II 30 63 46 13 6 oo 9 04 25 37 74 17 4 42
small quantities also of ZrC>2, Ce02, La203, DOs, YgOs, Er2C>3, MnO, Alkalies, SiOs and P20s These analyses are interpieted as indi- cating that the mineral is a uranium salt of uramc acid, U02(OH)2, or
H2U04, thus Udr , or U30S, in which Pb replaces the U in
part, and Th02 the UC>2 Radium is found in most specimens and helium in nearly all
Several varieties aie recognized, the distinctions being based largely upon chemical differences
Broggente has UOa to other bases as i : i
Cleweite and nnvemte contain 9 per cent to 10 per cent of the yttna earths
Pitchblende is possibly an amorphous urammte containing a very little thona and much water Its specific gravity is often as low as 6 5, due probably to partial alteration
Urammte crystallizes in the isometric system in octahedrons, and m combinations of 0(ui), oo 0(no), and oo 0 oo (100) Crystals are rare, however, the material usually occurring in crystalline masses and in botyroidal groups
The mineral is gray, brown or black and opaque. Its streak is brownish black, gray or olive green. Its luster is pitch-like or dull Its fracture is uneven or conchoidal It is brittle, its hardness is 5 5 and density 9-9 7 Like the other uranium minerals it is radioactive
Before the blowpipe uraninite is infusible. Some specimens color the flame green with copper With borax it gives a yellow bead in the oxidizing flame, turning green in the reducing flame All specimens give reactions for lead and many for sulphur and arsenic The mineral is soluble in nitric and sulphuric acids, with slight evolutions of helium,
Oolumbates, Tantalates And Uranates 299
the ease of solubility increasing with the increase in the proportion of rare earths present
Urammte is distinguished from wo'Jramite, samarsktfe, columbde and tantahte, by lack of cleavage, greater specific gravity, and differences in crystallization From all but samarskite it is also distinguished by the reactions for uranium and, m the case of most specimens, by the reac- tion for lead It is especially characterized by its pitch-black luster
Occurrence and Localities — Urammte occurs in pegmatites and in veins associated ith silver, lead, copper and other ores It is found m the ore veins in Saxony, Bohemia, and in pegmatites near Moss, Arendal and other points in Norway
In the United States it occurs in pegmatites at Middletown and B ranch ville, in Connecticut, at the Mitchell County mica mines, North Carolina, and at Barnnger Hill, Llano County, Texas It is also found m large quantity near Central City, Gilpin County, Colorado, where it is associated with gold, galena, tetrahednte, chaicopynte and other ore mineials
Production — Urammte has been mined in small quantity in Colo- rado, and at Barnnger Hill, both as a source of uranium and as a source of radium In Cornwall, England, and at Joachimsthal, Austria, it is mined as a source of radium (See also p 292.)
Chapter Xvi
The Silicates
THE silicates are salts of various silicon acids, only a few of which are known uncombmed with bases The silicates include the commonest minerals and those that occur in largest quantity They make up the greater portion of the earth's crust, forming most of the igneous rocks and a large portion of vein fillings In number, the silicates exceed all other mineral compounds, but because of their stability they are of very little economic importance A few are used as the sources of valuable substances, and their aggregates, the sihcious rocks, are utilized as building stones, but, on the whole, they are of little commercial value Since, however, they occur in good crystals and their material is trans- parent in thin sections so that it can easily be studied by optical methods, they are of great scientific importance Much of the progress made in crystallography has been accomplished through the study of these com- pounds
Although the salts of the silicic acids are very numerous and most of them are very stable toward the ordinary reagents of the laboratory, the acids from \\hich they are derived are only imperfectly known The only one that has been prepared m the pure state is the compound KfeSiOa This occurs as a gelatinous (colloidal) white substance which rapidly loses water upon drying and probably breaks up into a number of other compounds which are also acids, containing, however, a larger proportion of silicon in the molecule than that in the original compound When the tetrafluoride, or the tetrachionde, of silicon is decomposed by water, the principal product is the acid referred to above, but m addition to this there is probably formed also the compound HaSiO* or Si(OH)4, which is the ortho acid Some silicates are salts of these acids. Others are salts of the acids containing a larger proportion of silicon In most cases, however, these acids may be regarded as belonging to a series in which the members are related to one another m the same manner as are normal sulphuric, common sulphuric and pyrosulphuric acids. Nor- mal sxilphuric acid is HeSOe By abstraction of aKkO the compound H2SO4, or ordinary sulphuric acid, results If from two molecules of EfcSOi, one molecule of HsO is abstracted, 1128307, or pyrosulphuric acid, is left. In the same manner all of the silicic acids may be regarded
Silicates 301
as being derived from normal silicic acid Si(OH)4 or H4SiO4 by the ab- straction of water, thus:
Orthosilicic acid is Metasihcic acid is H4Si04 -IOor H2SiOs, Diorthosilicic acid is 2H4Si04— IfeO or Dimetasilicic acid is 21*28103- EfeO or Tnmetasilicic acid is 31128103 — EfeO or
The compounds containing more than one silicon atom in the molecule are known as polysilicates The salts of metasilicic acid are meta- sihcates
Many attempts have been made to discover the chemical structure of the comparatively simple silicates and several proposals have been offered to explain the great differences often observed in the properties of silicates with the same empirical formula, but no explanation of these differences has thus far proved satisfactory The silicates are so very stable under laboratory conditions, and, when they are decomposed, their decomposition products are so difficult to study, that it has been impossible to determine their molecular volumes or to understand their substitution products We are thus driven to ascribe many of the anomalies in their composition to solid solutions, to absorption phenom- ena, and to the isomorphous mixing of compounds, some of which do not exist independently
There are many silicates, moreover, which cannot be assigned to any of the simple acids mentioned above, but which probably must be regarded as salts of very much more complex acids Others are pos- sible salts of alurninosiliac acids in which aluminium functions in the acid portions Thus, albite is usually regarded as a trisilicate, NaAlSisOg, and anorthite as an orthosihcate, CaAl2(Si04)2 But the two substances are completely isomorphous, and for this reason it is thought that they must be salts of the same acid If we assume an aluminosilicic acid of the formula HsAlSOg, albite may be written (NaSi) AlSi2Og, and anor- thite (CaAl)AlSi20g The two minerals thus become salts of the same acid and their complete isomorphism is explained The relations that exist among many silicates might be better understood on the assump- tion that they are salts of complex silicic and of aluminosilicic acids than on the assumption that they are salts of simpler acids, as is now the case But, since it has been impossible to isolate the acids and study them we are not certain as to their character It is, therefore, believed best to represent most silicates as salts of the simplest acids possible, consistent with their empirical compositions as determined by analyses
302 Descriptive Mineralogy
As in,the case of salts of other acids there are silicates that contain hydrogen and oxygen m such relations to their other components that when heated they yield water In some cases this water is driven off at a comparatively low temperature and the residue of the compound re- mams unchanged A compound of this kind is usually called a hydrate or the compound is said to contain water of crystallization In other cases a high temperature is necessary to drive off water, and the com- pound breaks up into simpler ones In these instances the water is said to be combined The compound is usually basic
In the descriptions of the silicates the order in which the minerals are discussed is that of increasing acidity, i e , increasing proportion of the Si02 group present m the molecule This order, however, is not fol- lowed ngorously The members of well defined groups of closely related minerals are discussed together even if their acidity varies widely Nearly all the silicates are transparent or translucent and all are elec- trical insulators
The Anhydrous Orthosilicates
NORMAL ORTHOSILICATES— R4SiO4 OLIVINE GROUP (R"aSi04) R"=Mg, Fe, Mn, Zn
The members of the olivine group are normal silicates of the metals Mg, Fe, Mn and Zn They constitute an isomorphous series crystalliz- ing in the holohedral division of the orthorhombic system (rhombic bi- pyramidal class) The most common member is the magnesium-iron compound (Mg Fe)2Si04, ohmne, or thrysot Ic, from which the group gets its name. The members with the simplest composition are for- st&rite (Mg2Si04), fayahte (FeaSiO and tephrotte (Mn2SiOj.) The others are isomorphous mixtures of these, with the exception of three rare minerals, of which one, monttcelhte, is a calcium magnesium silicate, another, tttanohwne, contains Ti in place of a part of the Si, and the other, roeppente, contains some Zn2Si04 Most of them are formed by crystallization from molten magmas
Crystals of all the members of the group are prismatic and all have nearly the same habit They are often flattened parallel to one of the pinacoids, oo P 56 (oio) or oo P 55 (100) The axial ratios of the com- moner members are as follows
Forstente a : b . 4666 : i : 5868 The angle iioAiTo=$o° 2'
Ohvine 4658 i : 5865 The angle no A 110=49° 57'
Tephroite 4600 . i : 5939 The angle no A 110=49° 24'
Fayahte 4584 : i : 5793 The angle iioAiTo=49°
°
Anhydrous Orthosilicates
Crystals of olivine are usually combinations of some or all of the following forms- oo P 56 (100), oo P 06 (oio), oP(ooi), ooP(no), ooP2(i2o),
Po6 (Oil), 2Po6(o2l), Poo(lOl),
P(ni) and 2P2(i2i) (Fig. 163) The crystals of fayahte are usually more tabular than those of olivine, but forsterite and tephroite crystals have nearly the same forms The cleavage of all is distinct parallel to oo P 66 (oio), less distinct parallel to oo P oo (100) in olivine, and par- allel to oP(ooi) in fayahte
The compositions of the pure Mg, Mn, and Fe molecules are
Fig
163— Olivine Crystals with ooP, no (m)t oop So, oio (b),
OP, 001 (c), 2P5,02l(&), 00 PI,
120 ($),P oo , ioi (d) and P, in (e)
MgO MnO FeO SiO2
Mg2Si04 Mn2Si04
Fe2Si04
All natural crystals, however, contain some of all the metals indicated and, in addition, many specimens contain also a determmable quantity of CaO and traces of other elements
Forsterite, Olivine and Fayalite (MfeSiO* - (Mg Fe)2Si04 -Fe2Si04)
The composition of olivine naturally depends upon the proportion of the forsterite and fayahte molecules present in it When the propor- tion of FeO exceeds 24 per cent, the variety is known as hyaderite A few typical analyses are quoted below
MgO
FeO
CaO
I 51 64
S °i
r 08
Ii 50 27
8S4
Iii 48 12
Iv 39 68
A1203 Si02
42 42 30
Total Sp Gr 100 45 3 261
Ioo Oo
99 81 3.294
I From masses enclosed m Vesuvian lava II Concretion in basalt near Sasbach, Kaiserstuhl
III Grams from glacial debris, Jan Mayen, Greenland
IV Grams from coarse-grained rock, near Montreal, Canada
304 Descriptive Mineralogy
In addition, there are often also present small quantities of Ni, Mn, and Ti
Forsterite, olive and fayalite are usually yellow or green in color and have a vitreous luster. Forsterite is sometimes white and ohvine often brown. All three minerals become brown or black on exposure to the air All are transparent or translucent Their streak is colorless or yellow The fracture of ohvine is conchoidal In the other two minerals it is uneven Their hardness, density and refractive indices for yellow light are as follows
Hardness Sp Gr a. ft 7
Forsterite 6-7 3 21-3 33 i 6319 i 6519 i 6698
Olivme. 6 5-7 3 27-3 37 i 6674 i 6862 i 7053
Fayalite 65 4 00-4 14 i 8236 i 8642 i 8736
Before the blowpipe most olivines and forsterites whiten but are in- fusible Their fusion temperatures are between 1300° and 1450°, decreasing with increase in iron Fayahte and varieties of ohvine rich in iron fuse to a black magnetic globule All three minerals are decom- posed by hydrochloric and sulphuric acids with the separation of gelat- inous silica , the iron-rich vaneties are decomposed more easily than those poor m iron
The minerals are characterized by their color and solubility m acids.
Both fayalite and ohvine alter on exposure to the air, the former changing to an opaque mixture of Fe20s and Si02, or to the fibrous mineral anthophylhte ((Mg-Fe)SiOs), and ohvine to a mixture of iron oxides and fibrous or scaly gray or green serpentine (BUMgaSOo). In other cases, under metamorphic conditions, the alteration is to a red lamellar mineral (iddingsite) which may be a form of serpentine, or to magnesite, or to the silicate, talc Other kinds of alteration of this mineral have also been noted but those descnbed are the most common
Syntheses — The members of the ohvine series have been produced by fusing together the proper constituents in the presence of magnesium and other chlorides They are, moreover, present in many furnace slags where they have been made in the process of ore smelting.
Occurrence — Ohvine occurs as an original constituent of basic igneous rocks and as a metamorphic product m dolomitic limestones It is found also in the form of rounded grains in some meteoric irons. Fayalite occurs in acid igneous rocks, especially where affected by pneumatolytic
Anhydrous Orthosilicates 305
action, and forsterite in dolomitic rocks they have been meta- morphosed by the action of igneous rocks
Localtes — Members of the olivine group occur m the basaltic lavas of many volcanoes — as those of the Sandwich Islands, in the limestone inclusions in the lava of Mt Somma, near Naples; in vanous basic rocks in Vermont and New Hampshire and at Webster, N C. At the latter place granular aggregates of almost pure ohvme constitute great rock masses known as dunite
Fayalite is found in the rhyohtes of Mexico, the Yellowstone Park and elsewhere, and in coarse granite at Rockport, Mass , and in the Mourne Mountains, Ireland
Forstente occurs in limestone enclosures in the lava of Mt Somma and at limestone contacts with igneous rocks at Bolton, Roxbury, and Littleton, Mass , and elsewhere.
Uses and Production.— The only member of the group that is of any economic importance is a pale yellowish green transparent ohvine, which is used as jewelry under the name of " peridot " Gem material is found at Fort Defiance and Rice, in Arizona, scattered loose in the soil The little grams came from a basic volcanic rock. The amount produced in the United States during 1912 was valued at about $8,100.
Tephroite (Mn2Si04)
Although tephroite is regarded as the manganese silicate it nearly always contains some of the forsterite molecule
Analyses of brown (I), and red (II), varieties from Sterling Hill gave
MnO FeO MgO CaO ZnO Loss SiOs Total
I 52 i 52 7 73 fc> 5 93 28 30 55 99 93
Ii 47 62 23 14 03 S4 4 77 35 73 99 2 7
The mineral is gray, brown or rose-colored and transparent or translucent Its streak is nearly colorless It is rarely found m crys- tals Its hardness is about 6 and its density 408 It is strongly pleochroic in reddish, brownish red and greenish blue tints Its inter- mediate refractive index for yellow light about i 80.
It is fusible with difficulty (fusing temperature =1200°), and is sol- uble in HC1 with separation of gelatinous silica It is distinguishable from other like-appearing minerals by its difficult fusibility and its reaction with HC1
Syntheses — Crystals of the mineral have been made by fusing to- gether Si02 and Mn02 in the proportion of i : 2, and by long-continued
306 Descriptive Mineralogy
heating of MnCb and Si02 in an atmosphere of moist hydrogen or carbon dioxide
Localities — -Tephroite occurs at Mine Hill and Sterling Hill, near Franklin, N J , where it is associated with franldmite, zmcite and troostite It is found also at Pajsberg in Sweden with other man- ganese minerals and magnetite, and at Langban, in Wermland, Sweden
Uses — The mineral is of little commercial value It is separated with other manganese minerals from the zinc ore of Franklin, N. J , and is smelted with these in the production of spiegeleisen,
WILLEMITE GROUP CVSiQO R"=Zn, Mn
The willemite group comprises the two minerals willemite (ZSiO*) and troostite ((Zn Mn)2SiC>4), of which the latter is rare Willemite occurs in small quantity only, but troostite is an important source of zinc at the Franklin locality in New Jersey Both minerals are found in crystals
Willemite and troostite crystallize m the rhombohedral hemihedral division of the hexagonal system (ditrigonal scalenohedral class), with the axial ratios
Willemite a ; i : o 6698 Troostite i . 0.6698
Willemite and Troostite (Zn2SiO4-(Zn Mn)2SiO4)
Willemite and troostite occur massive, in grains, and m simple crys- tals
The theoretical composition of willemite is 8102—2704 and ZnO 72 96, but nearly all natural crystals contain traces of other elements When a noticeable quantity of manganese is present, the compound is troostite Several analyses are quoted below
Si02 ZnO MnO FeO Total
Willemite from Stolberg, Germany 26 90 72 91 35 100 16
Willemite from Greenland 27 86 71 51 . 37 99 74
White troostite from Franklin, N J 27 20 65 82 6 97 23 100 22
Dark red troostite from Franklin, N J 27 14 64 38 6 30 i 24 99,00"
The crystals of willemite exhibit the forms ooR(ioTo), oop2(ii2o), oR(oooi),|R(3034) and -|R(oil2)(Fig 164). Twins, with$P2(3 3 6 10) as the twinning planes, are rare The crystals of troostite are even more simple, with oop2(ii2o) and R(ioli), usually the only forms
Anhydrous Orthosilicates 307
present, though -JR(oiT2), -(0332) and R3(2i3i) are also occa- sionally found The angle ion A 1101 63° 59' The cleavage of willemite is distinct parallel to oP(oooi), and of troostite distinct parallel to ooP2(ii2o), and less perfect parallel to R(ioTi) and cR(oooi)
Willemite is colorless, yellow, brown or blue Troostite is green, yellow, brown or gray The colored varieties of both minerals are translucent Colorless willemite is transparent Both minerals are vitreous in luster Their hardness is between 5 and 6 and density between 3 9 and 4 3 The refractive indices of willemite for yellow light are w=i 6931, e=i 7118
Both minerals glow when heated before the blowpipe and are fused with difficulty (about 1484°), and both gelatinize with HC1 Willem- ite gives the reaction for zinc with Co(NOa)2 on charcoal, and troostite gives, in addition, the reaction for manganese. FIG 164— Willemite Ciys-
Syntheses— Willemite crystals have been' td with -Pa, XMO (c),
made by the action of gaseous hydrofluo- W and
silicic acid upon zinc, and by the action of
silicon fluoride on zmc oxide at cherry-red temperature
Localities and Origin — Willemite occurs in comparatively small quan- tity at only a few places, associated with other zinc minerals. In America it is found in colorless and black crystals at the Merritt Mine near Socorro, New Mexico, associated with mimetite, wulfenite, cerussite, bante and quartz
Troostite occurs only at Sterling Hill and Franklin Furnace, N J , but in such large quantity that it constitutes an important proportion of the zmc ore for which these localities are noted It is associated with franklmite and zincite. Both willemite and troostite are results of magmatic processes.
Phenacite (Be2Si(>4)
The theoretical composition of the compound BSiO* is SiO4= 54 47, BeO=45 S3 Many of the analyses of phenacite show that it ap- proaches very closely to this. A specimen from Durango, Mexico, for example, is:
SiO= 54 71, BeO=45 32, MgO+CaO= 14- Total- 100 17.
308 Descriptive Mineralogy
Phenacite crystallizes in the rhombohedral tetartohedral division of the hexagonal system with a : i i 0661 It occuis m crystals pos- sessing many different types of habit and with many different combina- tions of forms Perhaps oop2(ii2o), ooP(ioTo), R(ioTi), R3(2i3i) and — |R(oil2) are the most common (Fig 165) Interpenetration
twins are common at some localities The cleavage is indistinct parallel to oo P(ioTo) The angle loTi AIOI 63° 24'
Phenacite is colorless or white or some light shade of yellow or pink. It is trans- parent or translucent and has a glassy luster Its hardness is 7 5, and density about 3 and the refractive indices for yellow light are
FIG -Phenacite Crystal -i 6700 It'a infusible and
with oo p2, 1 1 20 (a), OOP, insoluble in acids When heated with a
-IPs - - little soda before the blowpipe it affords a
cent and pyroelectric
Colorless phenacite resembles quartz and Jerdente, and the yellow vanety topaz It is best distinguished from them by its crystalliza- tion
Syntheses — Small crystals have been made by the fusion of a mix- ture of Si02 and beryllium oxide and borax, and by melting together beryllium nitrate, silica and ammonium nitrate
Localities. — Phenacite occurs at the Emerald Mines near Ekaterin- burg in the Urals, near Fremont, in the Vogesen, at Reckmgen, in Switzerland, in Durango, Mexico, near Pike's Peak, at Topaz Butte, and at Mount Aratero, in Colorado, and at Greenwood, m Maine. In all cases the mineral is probably a result of pneumatolysis
Uses. — The colorless phenacite is used to a slight extent as a gem
GARNET GROUP (R"3R"'2(Si04)8) R"=Ca, Mg, Fe, Mn R'"=Al, Fe, Cr
The garnet group comprises a large number of isomorphous com- pounds, some of which are very common The members nearly all occur in distinct crystals that are combinations of isometric holohedrons (hexoctahedral class) Many different names have been given to the garnets and analyses show that they possess very different compositions With the exception of a few rare varieties, they can all, however, be explained as consisting of one of the six molecules indicated below, or of
Anhydrous Orthosilicates 309
mixtures of them The six molecules and the names of the garnets corresponding to them, together with their densities, are.
Caa Ala (8104)3 Grossulante or Hessomte Sp gr 4-3 6
Mg3Al2(Si04)3 Pyrope =37-38
MnaAk (8104)3 Spessattite ==41-43
Almandite 1-4.3
4)3 Andradite or Melamte 8-4 i
3 Uvarovite =34
The following table contains the calculated percentage composition of the several pure garnet molecules and the records of analyses of some typical varieties of the mineral
SiOs A12O3 FcfcOs Cr203 FeO MgO CaO MnO TiCfe Total
Ia 40 01 22 69 37 30 100 oo
Ib 42 01 17 76 5 06 13 35 01 20 100 17
IIa 44 78 25 40 29 82 100 oo
lib 40 92 22 45 5 46 8 ii 17 85 5 04 46 100 39
Ilia 36 30 20 75 . 42 95 100 oo
Illb 36 34 12 63 4 57 47 I 49 44 20 99 70
IVa 36 15 20 51 43 34 100 oo
IVb 37 61 22 70 33 83 3 61 i 44 i 12 100 31
Va 35 45 3i 49 33 06 100 oo
Vb 35 09 tr 29 15 2 49 24 32 80 36 100 48
Vc 26 36 22 oo i 25 30 72 tr, 21 56 101 89
Via 38 23 29 27 29 27 100 oo
VIb 36 93 5 68 i 96 21 84 i 54 31 63 99 58
Ia Theoretical composition of the grossulante molecule
Ib Green and red grossulante from the limestone at Santa Clara, Cal.
IIa Theoretical composition of the pure pyrope molecule
lib Pyrope from a pendotite in Elliot Co , Ky Also, HzO 10.
Ilia Theoretical composition of spessartite
Illb Spessartite from Amelia Court House, Va
IVa Theoretical composition of almandite
IVb Almandite from Sahda, Colo
Va Theoretical composition of andradite
Vb Andradite from East Rock, New Haven, Conn Also, HaO.35.
Vc Schorlomite from Magnet Cove, Ark
VIft Theoretical composition of uvarovite
VIb Uvarovite from Bissersk, Urals
The crystals of garnet are usually simple combinations of oo 0(no) (Fig. 166); 202(211) and often 301(321) (Figs 167 and 168), although all the other holohedrons are also occasionally met with. Their cleavage which is indistinct is parallel to oo 0(no).
Descriptive Mineralogy
When examined in polarized light many garnets, especially those occurring in metamorphic rocks, are doubly refracting and, therefore, have not the molecular structure belonging to isometric crystals This
FIG 166— Garnet Crystal. (Natural size ) Form ooQ (no)
Fig 167 Fig 168.
FIG 167— Garnet Crystals with coO, no (d) and 202, 211 FIG 168 —Garnet Crystal with d and n as in Fig 167 Also oo 02, 210 and 308
231 (s) '
phenomenon has been explained as due to several causes, the most rea- sonable explanation ascribing it to strains produced in the crystals upon cooling
Anhydrous Orthosilicates 311
The garnets vary in color according to their composition, the com- monest color being reddish brovin Their luster is Mtreous, their streak white, hardness 6-7 5, and density 3 4-4 3 They are transparent or translucent Most varieties are easily fusible to a light brown or black glass, -which in the case of the varieties rich in iron is magnetic arovite, however, is almost infusible Some garnets are unattacked by acids, others are partially decomposed
Garnets, when in crystals, are easily distinguished from other sim- ilarly crystallizing substances by their color and hardness Massive garnet may resemble tcsuuant'e, sphene, zircon or tzunnaine It is distinguished from zircon by its easier fusibility and from vesuviarnte by its more difficult fusibility, from tourmaline by its higher specific gravity, and from sphene by the reaction from titanium
Under the influence of the air and moisture garnets may be partially or entirely changed to epidote, muscovite, chlorite, serpentine, and oc- casionally to other substances
Grossularite, Essomte, Hessonite, or Cinnamon Garnet occurs principally in crystalline schists and in metamorphosed limestones, where it is associated with other calcium silicates It is found also in quartz ve;ns The mineral is white, bight yellow, cinnamon-brown or some pale shade of green or red. The lighter-colored varieties are transparent or nearly so Those that are colored are used as gems Much of the hyacvnfi of the jewelers is a red grossulante (seep 317) Its hardness is about 7 and its density 3 4-3 6 It is fairly easily fusible before the blowpipe. The refractive index of colorless vari- eties for yellow light is, i 7438
Good crystals of grossulante occur at Phippsburg, Raymond and Rumf ord, in Maine, and at many other places both in this country and abroad Bright yellow varieties are reported from Canyon City, Colo
Pyrope is deep red, sometimes nearly black. Its hardness is a little greater than 7 and its density 3 7 Its refractive index for yellow light is between i 7412 and i 7504 The pure magnesium garnet is unknown All pyropes contain admixtures of iron and calcium molecules Many pyropes are transparent Those with a dark red color are used as gems They occur principally in basic igneous rocks
The principal occurrence of the gem variety in this country is in Utah, near the Arizona line, about 100 miles west of Ganado, Ariz , where it is found lying loose m wind-blown sand
Rhodolite is a pale rose-red or purple variety from Macon Co., N C It consists of two parts pyrope and one of almandite.
312 Descriptive Mineralogy
Spessartite is hyacinth or brownish red, with occasionally a tinge of violet The purest varieties are yellow, but since there is nearly always an admixture of one of the iron molecules, the more usual color is reddish brown The mineral is usually transparent Its hardness is 7 or a little greater, and its density 3 77-4 27 Its refractive index for yellow light is i 8105 In the blowpipe flame it fuses fairly easily to a black, nonmagnetic mass, and with borax gives an amethyst bead It is found in acid igneous rocks and in various schists
Its best known occurrences in the United States are IP granite, at Haddam, Conn , in pegmatite, at Amelia Court House, Va , and in the lithophyse of rhyohtes, near Nathrop, in Colorado
Almandite is deep red, brownish red or black It is one of the com- monest of all garnets It furnishes nearly all the material manufactured into abrasives Transparent vaneties are also used as gems The min- eral has a hardness of 7 and over Its density is 4 1-4 3, and its refrac- tive index, n, for yellow light, is about i 8100 It is slightly decom- posed by HC1 Before the blowpipe it fuses to a dark gray or black magnetic mass It is found in granites and andesites, and also in various gneisses and schists and in ore veins
Its best known occurrences in North America are at Yonkers and at various points in the Adirondacks, N Y , at Avondale, Pa , and on the Stickeen River, in Alaska
Andradite, or meknite, is black, brown, brownish red, green, brown- ish yellow or topaz-yellow. The purest varieties are topaz-yellow or light green and transparent The former constitute the gem topawhte and the latter, demantwd The black variety, melamte, nearly always contains titanium It occurs m alkaline igneous rocks, in serpentine, in crystalline schists and in iron ores The most titamferous varieties are known as schorlomtte The hardness of andradite is about 7 and its density between 3 3 and 41 n for yellow light i 8566 It is fusible before the blowpipe to a black magnetic mass
The mineral is very widely spread It occurs at Franklin, N J , m metamorphosed limestone, near Francoma, N H , in quartz veins, and at many other places A black titamferous vanety occurs in a meta- morphosed limestone in southwestern California and near Magnet Cove, m Arkansas The vanety found at Magnet Cove is schorlormte It is a black glassy mineral associated with brookite (TiCfe), nephdme (p 314), and thomsomte (p 455)
Common garnet is a mixture of the grossularite, almandite and
Anhydrous Orthosilicates 313
andradite molecules It occurs in many metamorphosed igneous rocks and in some slates
Uvarovite is emerald-green It is rare, occurring only with chromite in serpentine at Bissersk and Kyschtim in the Urals and in the chromite mines at Texas, Penn , and New Idria, Cal Its hardness is about 7 and density 3 42 Its refractive index for yellow light is i 8384 It is infusible before the blowpipe but dissolves in borax, producing a green bead
Syntheses — Garnet crystals have been produced by fusing 9 parts of nephelme and i part of augite (p 374) The fusion results in a crystalline mass of nephelme, in which spinel and melamte crystals are embedded
Occurrence — The members of the garnet group are widely spread in nature They occur in schists, slates and other regionally metamor- phosed rocks, in granite, rhyohte and other igneous rocks, and as con- tact products in limestones They are found also in quartz veins, in pegmatite, and associated with other silicates in ore veins. In some instances they separated from a cooling magma, in others they are the products of pneumatohtic process, and in others they are the results of contact and dynamic metamorphism
Uses and Production — The varieties that are transparent are used as gems Other varieties are crushed and employed as abrasives The value of the gem material produced in the United States in 1912 was $860 The production for abrasive purposes was 4,182 short tons, val- ued at $137,800 All of this was produced in the mountain regions of New York, New Hampshire and North Carolina The rock is crushed and the garnet separated by hand picking, screening, or by jigging The crushed material is used largely in the manufacture of garnet paper
Nepheline Group
The nephelme group of minerals includes three closely related com- pounds, of which nepheline is the most common They are all alumino- silicates of the alkalies Nephelme appears to be a solution of Si02, or of albite, in isomorphous mixtures of the orthosilicates, NaAlSiO± and KAlSiO* in the proportion of 8 molecules of the silicates to one of Si02, thus
8(Na K)AlSi04+Si02=(Na K)0((Na- K) AlSi03)2Al6(Si04)7
The other two members of the group are eucryptite (LiAlSKX) and kdhopkOOe (KAlSiQ*).
314 Descriptive Mineralogy
The members of the group crystallize in the hexagonal system and are apparently holohedral, but nephelme is hemihedral and hemi- morpmc (hexagonal pyramidal class) At temperatures above 1,248° the nephelme molecule crystallizes also in the trichmc system as car- negieite (see p. 418),
Nephelme
Although approximately a potash-soda silicate, nearly all specimens of nephelme contain more or less CaO and nearly all contain small quantities of water All contain an excess of SiCte To avoid the necessity of assuming the existence of this SiCb m solution with (Na K)AlSi04, it has been suggested that the variable composition of the mineral may be explained by regarding it as a solid solution of NaAlSisOg and CaAkSOs (best known in their trichmc forms as albite and anorthtte) in an isomorphous mixture of the two molecules, NaAlSi04 and KAlSiO* The average of five analyses of crystals from Monte Somma, Italy, is shown in I, and the composition of a mass of the mineral from Litchfield, Maine, in II
Si02 A1203 CaO MgO Na20 KaO H20 Total
I 44 08 33 28 i 57 19 16 oo 4 76 15 100 03
II 43 74 34 48 tr tr 16 62 4 55 86 100 25
When found in crystals, the mineral is apparently holohedral in form with an axial ratio i 8389 The crystals are nearly always short columnar in habit and usually consist of very simple combinations The most prominent forms are ooP(ioTo), oop2(ii2o), oP(oooi),
2P(202l), P(lo7l), |P(loT2) and 2P2(lI2l)
(Fig 169) Their cleavage is imperfect parallel toooP(ioIo) and oP(oooi)
Nephelme is glassy, white or gray and trans- parent, when occurnng as implanted crystals FIG i69--NepheUneCrys- The translucent va™*y with a glassy luster tal with oP, oooi (c), occurs ln rocks is known as eleohte This oo p, iolo P, loir variety may be gray, pink, brown, yellowish or (p) andoop2, 1120 (a) greenish The streak is always white The fracture of both forms is conchoidal or uneven; hardness, 5-6 and density, 2 6 For yellow light, co= 1.5424, i 5375.
Anhydrous Orthosilicates 315
Before the blowpipe nephelme melts to a \\hite or colorless blebby glass At 1,248° it passes over into carnegieite \\hich melts at 1,526° It dissolves in hydrochloric acid with the production of gelatinous silica Its powder before and after roasting reacts alkaline
The mineral is distinguished from other silicates by its crystalliza- tion, gelatinization with acids, and hardness The massive varieties are often distinguishable by their greasy luster
Nephelme alters to various hydrated compounds, especially to the zeolites (p. 445), and to gibbsite, muscovite, cancnmte and sodahte
Syntheses — Nephelme has been prepared by fusing together AfeOa, SiO2 and Na2C03, and by the treatment of muscovite by potassium hydroxide.
Occurrence — The mineral occurs principally as an original constit- uent of many igneous rocks, both plutomc and volcanic, and also as crystals on walls of cavities in them
Locates —Crystals occur near Eberbach, in Baden, in the inclu- sions within volcanic rocks at Lake Laach, in Rhenish Prussia, in the older lavas of Monte Somma, Naples, Italy, at Capo de Bove, near Rome, in southern Norway, and at various other points in southern Europe Massive forms are found m coarse-brained rocks near Litch- field, Maine, Red Hill, N H , Magnet Cove, Ark., m the Crazy Mts , Mont , and at other places
Cancrinite
Cancnmte is extremely complex in composition It is nearly allied to nephelme but contains a notable quantity of C02 It corresponds approximately to an hydrated admixture of Na2COs and 3NaAlSi04, in which some of the Na is replaced by K and Ca Specimens from Barkevik (I) in Norway, and from Litchfield (II), in Maine, yield the following analyses:
Si02 AkOs Fe203 CaO Na20 K2O C02 EfeO Total I 37 01 26 42 7 19 18 36 7 27 3 12 99 37
II. 36 29 30 12 tr. .4 27 19 56 18 6 96 2 98 100 36
Cancrinite is hexagonal (dihexagonal bipyramidal class).
Crystals are rare, and those that do exist are very simple, prismatic forms bounded by ooP(ioTo), ooF2(ii2o), oP(oooi) and P(ioTi) Their axial ratio is i : 4410
316 Descriptive Mineralogy
The mineral is usually found without crystal planes It is colorless, white or some light shade, such as rose, bluish gray or yellow Its streak is \vmte, its luster glassy, greasy or pearly and it is translucent Its cleavage is perfect parallel to ooP(ioTo) and less perfect parallel to oo P 2 1 1 20) Its break is uneven, hardness 5 and density 245 For red light* 5244? 49S5
Before the blowpipe the mineral loses its color, swells and fuses to a colorless blebby glass In the closed glass tube it loses CCb and water, and becomes opaque After roasting it is easily attacked by weak acids with effervescence and the production of gelatinous silica When boiled with water Na2COs is extracted in sufficient quantity to give an alkaline reaction
Cancrimte is easily distinguished by its effervescence with acids and the production of gelatinous silica
Synthesis — Small colorless, hexagonal crystals with a composition corresponding to that of cancnmte, have been made by treating mus- covite with a solution of NaOH and NasCOs at 500°
Occurrence — The mineral occurs principally as an associate of neph- elme in certain coarse-grained igneous rocks In some cases it appears to be an original rock constituent and in others an alteration product of nephelme It sometimes alters to natrohte (see p 454), foiming pseu- domorphs
Localities — Cancrimte is found in rocks at Ditro, Hungary, at Barkevik and other localities in southern Norway, where it occurs m pegmatite dikes, m the parish of Kuolajarvi, in Finland, and in nephelme syenite at Litchfield m Maine,
Zircon Group
The orthosihcates of zirconium, zircon, and of thorium, thorite, con- stitute a group, the members of which possess forms that are almost identical with those of rutile, cassitente and xenotime Indeed, parallel growths of zircon and xenotime are not uncommon. Formerly zircon was grouped with the two oxides.
Zircon and thorite are tetragonal (ditetragonal bipyramidal class), with approximately the same axial ratios and the same pyramidal angles. The two minerals are completely isomorphous
Zircon ZrSiO* a ' 6391 in A ill 56° 37', Thorite ThSi04 =6402 =56° 40'.
Zircon is fairly common Thorite is rare.
Anhydrous Orthosilicates
Zircon (ZrSiO4)
Zircon, like rutile, is a fairly common compound of a comparatively rare metal It is practically the only ore of the metal zirconium. It is found mainly in crystals and as gravel
Although some specimens of zircon contain a large number of ele- ments, others consist only of zirconium, silicon and oxygen in propor- tions that correspond to the formula ZrSiO*, which demands 67 2 per cent ZrO and 32 8 per cent SiOg
Its axial ratio is a : r=i ' 6301 Its crystals are usually simple combinations of °o P(uo) and P(m), with the addition of oo P oo (100)
Fig 170
Pig 171
FIG. 170 — Zircon Crystals with P, no (w), ooPoo, 100 (a), 3?, 331
P, in (p) andsPs, 311 (x) FIG 171 — Zircon Twinned about P (101) (221)
and often 3P3(3ii) (Fig 170) Elbow twins, like those of rutile and cassitente, are known (Fig 171)
The cleavage of zircon is very indistinct. Its fracture is conchoidal. Its hardness is 7.5 and density about 4 7 The mineral varies in tint from colorless, through yellowish brown to reddish brown Its streak is uncolored and luster adamantine Most varieties are opaque, but transparent varieties are not uncommon The orange, brown and red- dish transparent kinds constitute the gem known as hyacinth The refractive indices for yellow light are* 9302, 6=1,9832.
Zircon is infusible, though colored varieties often lose their color when strongly heated In the borax and other beads the mineral gives no preceptible reactions. In fine powder it is decomposed by concen- trated sulphuric acid. When fused with sodium carbonate on platinum it is likewise decomposed, and the solution formed by dissolving the fused mixture in dilute hydrochloric acid turns turmeric paper orange. This is a characteristic test for the zirconium salts.
318 Descriptive Mineralogy
The mineral is easily recognized by its hardness, its resistance toward reagents and its crystallization
Syntheses —Small crystals of zircon are obtained by heating for sev- eral hours in a steam-tight platinum crucible a mixture of gelatinous silica and gelatinous zirconium hydroxide Crystals have also been, made by heating for a month a mixture of ZnCb and SiOa with 6 times their weight of lithium bimolybdate
Occurrence and Ongin —Zircon is widely spread in tiny crystals as a primary constituent in many rocks, and in large crystals in a few, notably in limestone and a granite-like rock known as nephelme syenite In limestone it is a product of contact action. It occurs also in sands, more particularly in those of gold regions, and abundantly in a sand- stone near Ashland, Va
Localities —The principal occurrences of the mineral are Ceylon, the home of the gem hyacinth, the gold sands of Australia, Arendal, Hakedal and other places in Norway; Litchfield and other points in Maine, Diana, m Lewis Co , and a large number of other places in New York, at Reading, Penn , Henderson and other Counties, m North Carolina and Templeton, Ottawa Co , Quebec
Uses.— Zircon is the principal source of the zirconium oxide emplo)'ed in the manufacture of gauze used in incandescent gas lights and in the manufacture of cylinders for use in procuring a light from the oxyhydro- gen jet. The mineral has been mined for these purposes in Henderson Co , North Carolina
Transparent orange-colored zircons are sometimes used as gems since they possess a high index of refraction and consequently have a great deal of " fire " These are the true hyacinth The mineral often called by this name among the jewelers is a yellowish brown garnet
Production— k small quantity of zircon is usually obtained from Henderson Co., N C , but it rarely amounts to more than a few hundred pounds. The mineral occurs in a pegmatite and the soil overlying its outcrop. It is obtained by crushing the rock and hand picking Usually there is a little also separated from the sands in North Carolina and South Carolina that are washed for monazite. A pegmatite dike, rich in zircon, is also bemg prospected in the Wichita Mountains, Okla,, but no mining has yet been attempted.
Anhydrous Orthosilicates
Thorite (ThSiO4)
Thorite occurs in simple crystals bounded by ooP(no) and P(in) (Fig 172), and in masses The mineral is always more or less hydrated, but this is believed to be due to partial weathering It is black or orange- yellow (prangeite), has a hardness of 5 and a specific gravity of 4 5-5 for black vaneties and 5 2-5 4 for orange varieties Its streak is brown or light orange Hydrated specimens are soluble in hydro chloric acid with the production of gelatinous silica The min- eral occurs as a constituent of the igneous rock, augite-syemte, at several points m the neighborhood of the Langesundfjord, Norway,
FIG 172 — Thonte Crystal with oc P, no (m) and P;
Basic Orthosilicates Andalusite Group
Three compounds with the empirical formula AkSiOs exist as min- erals, kyamte, or disthene, andalusite and silhmanite. The first named is less stable with reference to chemical agents than the other two, but at high temperatures both kyamte and andalusite are transformed into silhmanite Kyamte is regarded as a metasihcate (AlOSiOa. The other two are thought to be orthosilicates (Al(A10)SiC>4) The latter are orthorhombic and both possess nearly equal prismatic angles They differ markedly, however, in their optical and other physical properties and, therefore, are different substances Kyamte is tnchnic For this reason and because of its different composition it is not re- garded as a member of the andalusite group A fourth mineral, topaz, differs from andalusite in containing fluorine. Often this element is present in sufficient quantity to replace all of the oxygen in the radical (A1O) In other specimens the place of some of the fluorine is taken by hydroxyl (OH). The general formula that represents these varia- tions is A1(A1(F OH)2)Si04 The mineral crystallizes in forms that are very like those of andalusite, and if corresponding pyramids are selected as groundforms their axial ratios are nearly alike. Unfortunately, however, different pyramids have been accepted as groundforms, and therefore the similarity of the crystallization of the two minerals has been somewhat obscured Daribunte, another mineral that crystallizes m the orthorhombic system with a habit like that of topaz is often also placed in this group, although it is a borosilicate, thus CaB2 (8104)2-
Descriptive Mineralogy
If 4P2(24i) be taken as the groundform of andalusite, 3(331) as that of topaz and 3? (331) as that of danbunte, the corresponding axial ratios would be
Andalusite a b . 5069 i i 4246 Topaz 5281 I 43*3
Danbunte 5445 44°2
These, however, are not the accepted ratios, since other and more prom- inent pyramids have been selected as the groundforms
Andalusite and Sillimanite (Al(AlO)SiO4)
Andalusite and sillimamte have the same empirical chemical compo- sition and crystallize with the same symmetry, which is orthorhombic holohedral (rhombic bipyramidal class), but they have different physical properties and different crystal habits, and hence are regarded as dif- ferent minerals The theoretical composition of both is
8102=3702,
Total= 16000
Nearly all specimens when analyzed show the presence of small quantities of Fe, Mg, and Ca, but otherwise they correspond very closely to the theoretical composition
Both minerals are characteristic of metamorphosed rocks, but andalusite occurs principally in those that have been metamorphosed by
contact with igneous mtru- sives, while Sillimanite is especially characteristic of crystalline schists and, in gen- eral, of rocks that were dy- namically metamorphosed It also occurs with ohvme as in- clusions in basalt lavas Silh- FIG 173— Andalusite Crystals with oop, no mamte is more stable at high (m), oP ooi (c), M, oii M, -op a, loo temperatures than andalusite (b), oo Poo, oio (a), oo P2, 210 (/), cc™~ r
120 Poo, ioi (r), P, in (p) and
121 (k)
When m contact rocks it is found nearer the intrusive
than andalusite
Andalusite— The accepted axial ratio of andalusite is 986*1 : i : 7024 Its crystals are columnar in habit and are usually simple combinations
Of 00 P 00 (IOO), 00 P 00 (OIO), OP(OOI), 00 P(lio), 00 P2(2IO), 00 P2(l2o)
Poo (ioi), Poo (on) with sometimes P (in) and 2P2(i2i) (Fig 173). The angle no A 110=89° 12'
Anhydrous Orthosilicates 321
The mineral, when fresh, is greenish or reddish and transparent Usually, however, it is more or less altered, and is opaque, or, at most, translucent, and gray, pink or violet Its cleavage is good parallel to oo P(no) and its fracture uneven Its hardness is 7 or a little less and its density 3 1-3 2 In some specimens pleochroism is marked, their colors being olive-green for the ray vibrating parallel to a, oil-green for that vibrating parallel to b and dark red for that vibrating parallel to c For yellow light the indices of refraction are 01=16326, 1(3=16390, 7=1 6440
Before the blowpipe the mineral gradually changes to sillimamte and is infusible When moistened with cobalt nitrate and roasted it becomes blue It is insoluble in acids
The mineral is distinguished by its nearly square cross-section, its hardness, its mfusibihty, and the reaction for Al, and by its manner of occurrence in schists and metamorphosed slates
Some specimens contain as inclusions large quantities of a dark gray or black material, which may be carbonaceous, arranged m such a way as to give a cross-like figure in cross-sections of crystals. Because of the shape of the figure exhibited by these crystals, this variety was early called chiastohte, and was valued as a sacred charm.
Andalusite alters readily to kaolin (p 404), muscovite (p 355), and sillimamte It has not been produced artificially
Occurrence — Andalusite is found principally in clay slates and schists that have been metamorphosed by contact with igneous masses, and to a less extent m gneisses
Localities — Its principal occurrences are in Andalusia, Spain, at Braunsdorf, Saxony, at Gefrees, in the Fichtelgebirge, in Minas Geraes, Brazil, and m the United States at Standish, Maine, Westford, Mass , and Litchfield, Conn Chiastohte occurs at Lancaster and Sterling, Mass
Use — The only use to which andalusite has been put is as a semi- precious stone, and for this purpose only the chiastolite variety is of any value
SiUimanite, or fibrokte, occurs principally m acicular or fibrous aggregates, on the individuals of which only the prismatic forms ooP(no) and °oP|(23o) and the macropmacoid ooPw(ioo) can be detected End faces are not sufficiently developed to warrant the determination of an axial ratio The relative values of the a and b axes are 687 : i. The angle iioAiio*80.
While most of the fibers correspond m composition very closely to the
322 Descriptive Mineralogy
theoretical value demanded by the formula Al(A10)Si04, many contain small quantities of Fe20a, MgO and HkO
The mineral is yellowish gray, greenish gray, olive-green or brownish It has a glassy or greasy luster and when pure is transparent Most specimens, however, are translucent, and many of the colored varieties show a pleochroism in brown or reddish tints Its cleavage is perfect parallel to oo P 55 (100) Its needles have an uneven fracture trans- versely to their long directions Their streak is colorless, hardness 6-7 and density 3 24 The mdices of refraction for the lighter colored varieties are a=i 6603, j8= i 6612, 7— i 6818 for yellow light
Sillimanite reacts similarly to andalusite toward reagents and before the blowpipe It is distinguished from other minerals by its habit and manner of occurrence.
This mineral is much more resistant to weathering than is andalusite It is, however, occasionally found altered to kaolin On the other hand, it is known also in pseudomorphs after corundum
Synthesis —It has been produced cooling fused silicate solutions rich in aluminium
Occurrence — Sillimanite is very widely spread in schistose rocks, especially those that have been formed from sediments It is essentially a product of dynamic metamorphism, but is formed also bv contact metamorphism, m which case it is found near the intrusive, where the temperature was high
Localities — Its principal occurrences in North America are in quartz veins cutting gneisses at Chester, Conn , at many points in Delaware Co , Penn , and at the Culsagee Mine, Macon Co , N C At the latter place and at Media in Penn , a fibrous variety occurs m such large masses as to constitute a schist — known as fibrohte schist.
Topaz (Al(Al(F-OH)2)Si04)
Topaz is a common constituent of many ore veins and is often present on the walls of cracks and cavities in volcanic rocks It occurs massive and also in distinct and handsome crystals
The mineral has a varying composition, which is explained in part by the fact that it is a mixture of the two molecules Al(AlF2)SiO4 and Al(Al(OH)2)SiOi The theoretical composition of the fluorine molecule is 8102=32 6, A1203=SS 4, F=2o 7=108 7, deduct (0 2F)8 7 loo.oo. A specimen from Florissant, Colo , gave.
F=i6 04=106 20-6 7s(0=F) 99 45.
Anhydrous Orthosilicates
Crystals of topaz appear to be orthorhombic (rhombic bipyramidal class), but the fact that they are pyroelectnc and that they frequently exhibit optical phenomena that are not in accord with the symmetry of orthorhombic holohedrons suggests that they may possess a lower grade of symmetry On the assumption that the mineral crystallizes with the symmetry of orthorhombic holohedrons the axial ratio of fluorine varie- ties is 5281 i 4771 l With the increasing presence of OH, however, the relative length of a increases and that of c diminishes The angle noAiTo=55° 43'-
The crystals are usually prismatic in habit with ooP(no) and oo P?(i2o) predominating They are notable for the number of forms
Fig 174 Fig 175.
FIG 174 — Topaz Crystals with oo P, no (m), oo pT, 120 (Z), P, in (u), 2P, 221 (o)
4? oo , 041 00 and oo P oo , oio (6)
FIG 175 — Topaz Crystal with m, I, n and y as in Fig 174. Also 2? oo , 021 (/), oo , 043 and 2P 55 , 201 (d)
that have been observed on them, especially in the prismatic zone and among the brachypyramids The number of the latter that have already been identified is about 45
The three types of crystals that are most common are shown in Figs 174, 175 and 176 Their most prominent forms are ooP(no), ooP2(i2o), Poo (on), P(ni), |P(223), 4? (041), oo PJ (130) and oP(ooi). Often planes are absent from one end of the vertical axis, but since the etch figures on the prismatic planes do not indicate hemi- morphism, the absence of the lacking planes is explained as being due to unequal growth The planes of the prismatic zone are usually striated
The mineral is colorless, honey yellow, yellowish red, rose and rarely bluish. When exposed to the sunlight the colored varieties fade, and
The more commonly accepted axial ratio is a : 6 : c- £p(22i) 'being taken as the groundfonn*
5285 : i : .9539, the form
Descriptive Mineralogy
fj d, 0 and tt as m Figs 174 and 175 Also §P, 223 (z), oP, ooi (c) and 4P 55 , 401 (p)
when intensely heated some honey-yellow crystals turn rose-red Its cleavage is perfect parallel to oP(ooi) and imperfect parallel to P 06 (on) and P oo (101) The hardness of the mineral is 8 and its density 3 5-3 6 Its refractive indices for yellow light are i 6072, i 6104, i 6176 for a variety containing very little OH, and 05=16294, £=16308,
7=16375 for a variety rich m hydroxyl The indices of refraction being high, the mineral when cut exhibits much brilliancy — a feature which, together with its hardness, gives it much of its value as a gem.
Topaz is infusible before the blowpipe and is insoluble in acids
FIG 176— Topaz Crystal with m, I, y, At a high temperature it loses its
fluorine as silicon and aluminium fluorides The mineral also ex- hibits pyroelectncal properties, but these are apparently distributed without regularity m different crystals Many crystals contain inclusions of fluids containing bubbles, and sometimes of two immiscible fluids the nature of which has not yet been determined It has been thought that the principal fluid present is liquid carbon-dioxide or some hydrocarbon
The mineral is distinguished from yellow quartz by its crystalliza- tion, its greater hardness and its easy cleavage
Topaz is frequently found coated with a micaceous alteration product which may be steatite (p 401), muscovite (p 355) or kaolin (p 404)
Synthesis — Crystals have been made by the action of hydrofluosihcic acid (EfeSiFe) upon a mixture of silica and alumina m the presence of water at a temperature of about 500°.
Occurrence — The mineral occurs principally in pegmatites, espe- cially those containing cassitente, in gneisses, and in acid volcanic rocks In all cases it is probably the result of the escape of fluorine-bearing gases from cooling igneous magmas.
LocalMes —Topaz is found in handsome crystals at Schneckenstem in Saxony, in a breccia made up of fragments of a tourmalme-quartz rock cemented by topaz. It occurs also in the pegmatites of the tin mines m Ehrenfnedersdorf, Marienberg and other places in Saxony, Bohemia, England, etc , on the walls of cavities in a coarse granite m Jekatennburg and the Hmengebirge, Russia, in veins of kaohn cutting a talc schist in Mrnas Geraes in Brazil; and in the cassitente-bearmg
Anhydrous Orthosilicates 325
sands at San Luis Potosi, Durango and other points in Mexico In the United States it occurs on the walls of cavities m acid volcanic rocks, at Nathrop, Colo , in the Thomas Range, Utah, and other places It occurs also in veins Tilth muscovite, fluonte, diaspore and other minerals at Stoneham, Maine, and Trumbull, Conn
Uses and Pi oduction — Topaz is used as a gem About 36 Ib , valued at $2,675, was produced in the United States in 1911. In the following year the production was valued at only $375.
Danburite (CaB2(Si04)2)
Danbunte, which is a comparatively rare mineral, is a calcium borosilicate with the following theoretical composition 8102=4884, B2Os 28 39 and CaO= 2277 Usually, however, there are present in it small quantities of AfeOs, Fe20s, MnaOs and EfeO Thus, crystals from Russell, New York, contain
SiO2 B2O3 Al203,etc H20 CaO Total
49 70 25 80 i 02 20 23 26 99 98
The mineral crystallizes in the orthorhombic system (rhombic bipy- ramidal class), with an axial ratio 5445 : i 4801 Its crystals are usually prismatic in habit They contain a great number of forms, of which oo P (100), oo P 06 (oio), co P2(i2o), oo P4(i4o), and oo P(iio) among the prisms, 2P4(i42), 2P?(i2i) among the pyramids and oP(ooi) are the most prom- inent (Fig. 177). The angle iioAiib= 57° 8'.
When fresh and pure the mineral is trans- parent, colorless or light yellow, but when more or less impure is pink, honey-yellow or dark brown Its streak is white, and luster vitreous Its cleavage is imperfect parallel to JTIG I77 —Danbunte Cr>s- oP(ooi) and its fracture uneven or conchoidal tal with oop, no (m), Its hardness is about 7 and density 2 95-3 02 °°p2, 120 (Z), PSo , 101
Its refractive indices for vellow light are <r)"d4P-,
041 (w) a=l 6317, 0=1 6337, 7=1 6383
Before the blowpipe the mineral fuses to a colorless glass and colors the flame green It is only slightly attacked by hydrochloric acid, but after roasting is decomposed with the formation of gelatinous silica. It phosphoresces on heating, glowing with a red light.
Origin — Danburite is probably always a product of pneumatolytic
m
326 Descriptive Mineralogy
action, as it is found m quartz and pegmatite veins in the vicinity of igneous rocks and on the walls of hollows within them
Locahtm —Its principal occurrences in this country are at Danbury, Conn , where it is in a pegmatite, and at Russell, N Y , on the walls of rocks and hollows in a granitic rock Its principal foreign occurrence is at Piz Valatscha, in Switzerland.
EPIDOTE GROUP (CfcR'"i(OH)(Si(>4)i)
The epidote group comprises six substances, of which two are di- morphs with the composition Ca2Al,3 (OH) (SiOs Ca2Al2(A10H) (SiO-Os One of these, known as ztnstie, crystallizes in the orthorhombic system, and the other, known as dinozoivite, m the monochiuc system The other four are isomorphous with clmozoisite These are hancockite, epidote, piedmontite and allanite The composition and comparative axial ratios of the four commoner isomorphs are as follows (assuming JP(Ti2) as the groundform of clmozoisite)
Clmozoisite Ca2 Ala (OH) (8104)3 i 4457 . i i 8057
Epidote Ca*(Al Fe)8(OH)(Si04)s 15807 i i 8057, £=64° 36' Piedmontite Ca2(Al Mn)s (OH) (8104)3 i 6100 i i 8326, 64° 39' Allaxute Ca2(Al Ce Fe)s (OH) (8104)3 i SS°9 J 769*, 18=64° 59'
Clmozoisite is rare, though its molecule occurs abundantly m iso- morphous mixtures with the corresponding iron molecule m epidote
Zoisite (Ca2Als(OH)(Si04)3)
Zoisite is a calcium, aluminium orthosilicate containing only a small quantity of the corresponding iron molecule The theoretical composi- tion of the pure Ca molecule is
810=3952, Al20s=3392> CaO=24$9, H20=i97 Total=ioooo
Colored varieties contain a little iron or manganese Green crystals (I), from Ducktown, Tenn , and red crystals (thvtee) (II), from Kleppan, m Norway, analyze as follows
Si02 A1203 Fe203 FeO CaO MgO Mn203 Na20 H20 Total
I 39 61 32 89 91 71 24 So 14 2 12 100 88
II 42,81 31 14 2 29 18 73 i 63 i 89 64 99 13
Zoisite crystallizes m the orthorhombic system (orthorhombic bi- pyramidal class), with the axial ratio 6196 : i 3429. Its crystals are
Anhydrous Orthosilicates
usually simple and without end faces The most frequent forms are ooP(no), ooP4(i4o), oo P 06(010) P(in),2Pco(o2i)and4Po6(o4i) are the commonest terminations (Fig 178) The crystals are all pris- matic and are striated longitudinally Their cleavage is perfect parallel to oo P 86 (oio) The angle no A 110=63° 34'.
The mineral is ash-gray, yellowish gray, greenish white, green or red in color and has a white streak The rose-red variety, contain- ing manganese, is known as thuhte Very pure fresh zoisite is transparent, but the ordi- nary forms of the mineral are translucent Its luster is glassy, except on the cleavage surface, where it is sometimes pearly Its fracture is uneven Its hardness is 6 and density about 33 In specimens from Duck- town, Tenn , a=i 7002, /3=i 7025, 7=1 7058 for yellow light A notable fact in connection FIG 178— Zoisite Crystal with this mineral is that with increase of the with*)?, no(), ooPx,
molecule Ca2Fe3(OH)(Si04)3 in the mixture OIOJ6) °°p4'
sPoo, 021 (it) and P, in
'
the plane of its optical axes tends to change from oP(oio) to oo P 06 (ooi)
Zoisite fuses to a clear glass before the blowpipe and gives off water, which causes a bubbling on the edges of the heated fragments It is only slightly affected by acids, but after heating it is decomposed by hydrochloric acid with the production of gelatinous silica
Occurrence— The mineral occurs as a constituent of crystalline schists, especially those rich in hornblende, or of quartz veins traversing them It is also a component of the alteration product known as saussitnte which results from the decomposition of the plagioclase (p. 418) m certain basic, augitic rocks known as gabbros It is thus a product of metamorphism
Localities — Good crystals of zoisite are found near Pregratten in Tyrol, at Kleppan (thuhte), Parish Souland, Norway, and in the ore veins at the copper mines of Ducktown, Tenn , where it is associated with chalcopyrite, pynte and quartz.
Epidote (Ca2(Al-Fe)3(OH)(Si04)3)
Epidote, or pistazite, differs from the monochnic dimorph of zoisite (dmozoisite) in containing an admixture of the corresponding iron sfli- cate which is unknown as an independent mineral.
328 Descriptive Mineralogy
Since it consists of a mixture of an aluminium and an iron compound its composition necessarily vanes The four lines of figures below give the calculated composition of mixtures containing 15 per cent, 21 per cent, 30 per cent and 40 per cent of the iron molecule
Per cent
Si02
A1203
Fe203
CaO
H2O
Total
85
Most specimens contain small quantities of Mg, Fe, Mn, Na or K
Epidote is isomorphous with chnozoisite, crystallizing in the mono-
FIG 179— Epidote Crystals with °o P 55 , 100 (a), oP, 001(0), P w , 10! (r), 55 , 102 PI nI and P ob , on (0)
*FiG 180 — Epidote Crystals with a, c, r, wand 0 as m Fig 179 Also oop, iio(w), 2PS6, 2oT(0, -P55, ioi W, -3?!, W (/O and JP5, 423 (/)
clime system (monochmc prismatic class), with the axial ratio i 5787 i : 18036. #=64° 36'. The mineral is remarkable for its handsome crystals, many of which are extremely rich in forms The crystals are usually columnar in consequence of their elongation parallel to the b axis The most prominent forms are oo P 56 (100), oP(ooi), 56 (20!) P w (jol), P(nl), oo P(no) and P 5b (on) (Fig, 179 and 180) In addi- tion to these, over 300 other forms have been identified Twinning is common, with oop(ioo) the twinning plane The angle no A ilo= 109° 56'.
Epidote is yellowish green, pistachio green, dark green, brown or, rarely, red It is transparent or translucent and strongly pleochroic. In green varieties the ray vibrating parallel to the b axis is brown, that vibrating nearly parallel to c, yellow, and that vibrating perpendicular to
Anhydrous Orthosilicates 329
the plane of these two is green Its luster is glassy and its streak gray Its cleavage is very perfect parallel to oP(ooi) Its hardness is 6 5 and density 3 3 to 3 5 The refractive indices for yellow light m a crystal from Zillerthal are 05=17238, /5=i 7291, 7=1 7343 They increase with the proportion of the iron molecule present, being i 7336, i 7593 and i 7710 :n a specimen containing 27 per cent of the iron epidote
The varieties that have been given distinct names are.
BucUwidite, a greenish black variety in crystals that are not elon- gated,
Wtthanwte, a bright red variety containing a little MnO.
Fragments of the mineral when heated before the blowpipe yield water and fuse to a dark brown or black mass that is often magnetic With increase in iron fusion becomes more easy. Before fusion epidote is practically insoluble in acid. After heating HC1 decomposes it with the separation of gelatinous silica
The ordinary forms of the mineral are characterized by their yellow- ish green color, ready fusibility and crystallization
Occurrence and Origin — Epidote occurs in massive veins cutting crys- talline schists and igneous rocks, as isolated crystals and druses on the walls of fissures through almost any rock and in any cavities that may be in them, and as the pnncipal constituent of the rock known as epi- dosite It is a common alteration product of the feldspars (p. 408), pyroxenes (p 364), garnet, and other calcium and iron-bearing minerals Pseudomorphs of epidote after these minerals are well known. The mineral is a weathering product, but is more commonly a product of contact and regional metamorphism.
It has not been produced artificially
Localities — Epidote crystals are so widely spread that only a few of the important localities in which they have been found can be mentioned here. Particularly fine crystals occur m the Sulzbachtibal, Salzburg, Austria, in the Zillerthal, in Tyrol, near Zermatt, in Switzerland, in the Alathal, Traversella, Italy, at Arendal, Norway, in Japan, at Prince of Wales Island, Alaska, and at many other points in North America
Piedmontite (Ca2(Al-Mn)3(OH)(SiO4)3)
Piedmontite is the manganese epidote, differing from the ordinary epidote in possessing manganese in place of iron Usually, however, the iron and the manganese molecules are both present. Typical analy- ses of crystals from St. Marcel, in Piedmont, Italy (I), Otakisan, Japan (II), and Pine Mt , near Monterey, Md (III), follow
330 Descriptive Mineralogy
Si02 A1203 Mn203 MnO Fe203 MgO CaO H20 Total
I 35 68 18 93 14 27 3 22 i 34 24 32 2 24 100 oo
Ii 36 16 22 52 6 43* 9 33 40 22 05 3 20 100 53*
III 47 37 18 ss 6 85 i 92 4 02 25 15 82 2 08 100 05*
II contains also 44 per cent Na2<D The MOa contained also MnO
III contains also 2 03 per cent of the oxides of rare earths, 14 per cent PbO, ii per cent CuO, 23 per cent Na.O and 68 per cent KO The specimen contained also a little admixed quartz which was determined with the SiOj
The axial ratio of piedmontite is i 6100 i . i 8326 18=64° 39' Its crystals are similar m habit to those of epidote, but they are much simpler The most prominent forms are oo P 60 (100), oP(ooi), P(In), £P66(To2), ooP5b(oio) and ooP(no) Twins are fairly common, with oo P 56 (too) the twinning plane.
The mineral is rose-red, brownish red or reddish black It is trans- parent or translucent and strongly pleochroic in yellow and red tints and has a glassy luster and pink streak It is brittle, and has a good cleavage parallel to oP(ooi) Its hardness is 6 and density 3 40. Its refractive indices are the same as those of epidote.
Before the blowpipe piedmontite melts to a blebby black glass and gives the manganese reaction in the borax bead. It is unattacked by acids until after heating, when it decomposes m HC1 with the separation of gelatinous silica
It is characterized by its color and hardness and by its manganese reaction
Occurrence and Origin — Piedmontite occurs as an essential constit- uent of certain schistose rocks that are known as piedmontite schists It occurs also m veins and m certain volcanic locks, where it is probably an alteration product of feldspar. Its methods of origin are the same as those of epidote
Localities — Good crystals are found in the manganese ore veins at St. Marcel, Piedmont, on ilmenite in crystalline schists on the Isle of Groix, off the south coast of Brittany, and at a number of points on the Island of Shikoku, Japan, in crystalline schists and in ore veins In the United States it is so abundant m the acid volcanic rocks of South Mountain, Penn., as to give them a rose-red color.
Allanite (Ca2(Al-Ce-Fe)3(OH)(SiO4)3)
Allanite is a comparatively rare epidote m which there are present notable quantities of Ce, Y, La, Di, Er and occasionally other of the rarer elements Since cerium is present in the largest quantity the
Anhydrous Orthosilicates 331
formula of the mineral is usually written as above, with the under- standing that a portion of the cenum may be replaced by yttrium and the other elements Some idea of the complex character of" the numeral may be gained from the two analyses quoted below The first is of crystals from Miask, Ural, and the second of a black massive variety from Douglas Co , Colo
Si02 30 81 31 13
Al20s 16 25 ii 44
Fe2O3 6 29 6 24
Ce2O3 10 13 12 50
BeO 27
Di203 3 43
La203 635 Y203 i 24
FeO 8 14 13 59
MnO 2 25 61
MgO 13 16
CaO 10 43 9 44
K20 53 tr
Na20 56
H20 2 79 2 78
Total 98 77 99 8r
Allarute rarely occurs in crystals, but when these are found they are usually more complex than those of piedmontite but much less compli- cated than those of epidote. Their axial ratio is i 5509 : i : 1 7691 with £=64° 59' Their habit is like that of epidote crystals Common forms are ooFco(ioo), oP(ooi), °°P(iio) Twins are like those of epidote The mineral usually occurs as massive, granular or columnar aggregates, or as ill-defined columnar crystals resembling rusty nails It sometimes forms parallel mtergrowths with epidote.
It is black on a fresh fracture and rusty brown on exposed surfaces, and has a greenish gray or brown streak It has a glassy luster and is translucent in thin splinters, with greenish gray or brownish tints and is pleochroic in various shades of brown Its hardness is 5-6 and density 3-4, both varying with freshness and composition The cleav- ages are imperfect and the fracture uneven Its indices of refraction are nearly the same as those of epidote.
332 Descriptive Mineralogy
Small fragments of fresh allanite fuse to a blebby black magnetic glass before the blowpipe and are decomposed by HC1 with the separa- tion of gelatinous silica
Allamte is distinguished by its color, manner of occurrence, and the reaction for water in the closed tube
The mineral alters readily on exposure to the weather, yielding among other compounds mica and hmonite
Occurrence — Allanite occurs as an original constituent in some granites, and other coarse-grained rocks It is found also in gneisses, occasionally in volcanic rocks and rarely as a metamorphic mineral in crystalline limestones
Localities — The best crystals have been found m the druses of a volcanic rock at Lake Laach, Prussia, in coarse-grained granitic rocks at several places in the Tyrol, in the limestone at Pargas, Finland, and at various points in Ural, Russia Massive allanite occurs in the coarse granite veins at Hittero, Norway and as the constituents of granites at many places in the United States Parallel mtergrowths with epidote are found in granite at Ilchester, Md
Chondrodite Group
The chondrodite group of minerals includes four members of the general formula (Mg(F OHMgSiOy in which x equals i, 3, 5, 7, and y, i, 2, 3, 4 Of these, one (humite) may be orthorhombic The other three are monochmc with the angle £=90° The four members of the group with their compositions and axial ratios are
Prolectite (Mg(F OH)2)Mg(Si04) i 0803 i i 8862 18=90' Chondrodite (Mg(F OH)2)Mg3(SiO4)2 i 0863 i 3 1445 £=90
b Z
Humite (Mg(F OH)2)Mg5(Si04)3 i 0802 '1.4 4033 Clinohumtte (Mg(F OH)2)Mg7(Si04)4 r 0803 i 5 6588 £=90
To show the similarity in the ratios between the lateral axes of the four minerals, the & axis of humite is written as i Chondrodite, humite and clmohumite frequently occur together Chondrodite has been reported at more localities than either humite or clmohumite, but it is not certain that much of it is not chnohumite The three minerals resemble one another very closely They are relatively unstable under conditions prevailing at moderate depths in the earth's crust, passing easily into serpentine, brucite or dolomite Only chondrodite is de- scribed.
Anhydrous Orthosilicates
Chondrodite (Mg3(Mg(F-OHJ2)(Si04)2)
Chondrodite is a rather uncommon mineral that occurs mainly as a constituent of metamorphosed limestones that have been penetrated by gases and water emanating from igneous rocks It is a characteris- tic contact mineral
Its composition varies somewhat m consequence of the fact that OH and F possess the power to mutually replace one another The two analyses below are typical of varieties containing a maximum amount of F
Si02 MgO FeO H20 F F=0 Total
I 33 77 57 98 3 96 37 5 14=102 22—2 16 100 06 II 35 42 54 22 5 72 9 00=104 36-3 78 100 58
I. Crystals from, limestone inclusions in the lava of Vesuvius II. Grains separated from the limestone of the Tilly Foster Iron Mine, Brewster, N Y
Chondrodite is monoclmic (prismatic class), with an axial ratio i 0863 11:3 1445 18=90° The crystals vary widely in habit and are often complex The forms oP(ooi), oo P 66 (100), oo P oo (oio) and various unit and clmohemipyramids of the general sym- bol x?2 are frequently present, but other forms are also common (Fig 181) Twin- ning about oP(ooi) is also common Usually, however, the mineral occurs m little rounded grains, in some instances showing crystal faces, scattered through FIG 181 —Chondrodite Crys-
When fresh, Chondrodite has a glassy 1" ™v 2' "7 z£' 2' luster, is translucent and is white or has a _2p*2, 121 (r4)', — p, ni light or dark yellow, brown or garnet color (j), p, in (-2); It has a distinct cleavage parallel to oP(ooi), a conchoidal fracture, a hardness of 6 and a density of 3 15 Its refractive indices for yellow light are: 01=1607, £=1619, i 639
Before the blowpipe Chondrodite bleaches
without fusing With acids it decomposes with the production of gelatinous silica
103 to)> jP°°7 ioi (— &)
and — P, ioi (e%) The a axis runs from right to left and the upper left hand octant is assumed to be minus
334 Descriptive Mineralogy
It weathers readily to serpentine, chlorite and brucite, and conse- quently many grams are colored dark green or black
Occurrence — Chondrodite, as has been stated, occurs in meta- morphosed limestones It also occurs in sulphide ore bodies and m a few instances in magnetite deposits It is probably in all cases a pneu- matolytic or metamorphic product
Localities — It is found as crystals in the blocks enclosed m the lavas of Vesuvius, in the copper mines of Kapveltorp, Sweden, in limestone in the Parish of Pargas, Finland, and at the Tilly Foster Iron Mine, at Brewster, N Y It occurs as grams in the crystalline limestone of Sussex Co , N J , and Orange Co , N Y.
Datoltte Group
The members of the datolite group are four in number, but of these only two, viz, datohte (Ca(B OH)Si04) and gadohnite (Be2Fe(YO)2(Si04)2J are of sufficient importance to be described here Both minerals crystallize similarly in the monoclmic system ('mono- clinic prismatic class), with axial ratios that are nearly alike
Datolite a ' b c— 6345 i i 2657 89° 51' Gadohmte a b 6273 i 13215 89°
Datohte (Ca(B OH)SiO4)
Datolite, or dathohte, is characteristically a vein mineral
The composition corresponding to the formula given above is
218$; CaO=3Soo, Total =100 oo
Some specimens contain a little AbO,* and Fe20a but, m general, crystals that have been analyzed give results that are m close accord with the theoretical com-
FIG 182— Datohte Crystal Positlon'
oo POO, zoo (a), OOP, no (m), The mineral crystallizes in fine crys- -Poo, 101, — iPoo, 102 tals that are often very complicated (Fig -P, in -P3, 212 2) About 115 different forms have W, Poo, on (mv) and JPoo, been observed on Because of the
012 (g)
suppression of some faces by irregular
growth many of the crystals are columnar in habit, others are tabular. Most crystals, however, are nearly equi-dimensional The angle
ANHYDROUS ORTHOSILlCATES 335
no 1 10 -64° 40' The mineral occurs also in globular, radiating, granular and massi\ e forms
Datohte is colorless or white, when pure, and transparent Often, however, it is greenish, yellow, reddish or violet, and translucent. Its streak is white and its luster glassy It has no distinct cleavage Its fracture is conchoidal Its hardness is 5 and its sp gr about 3. Some crystals are pyroelectnc For yellow light, a- 16246, 0=1.6527, 7=1 6694
Before the blowpipe it swells, and finally melts to a clear glass and, at the same time, it colors the flame green Its powder before heating reacts strongly alkaline. After heating this reaction is weaker. The mineral loses water when strongly heated, and yields gelatinous silica when treated with hydrochloric acid.
The mineral is characterized by its crystallization, its easy fusibility and the flame reaction for boron
Synthesis — Datohte has not been produced artificially.
Occurrence, Origin and Localities — It occurs on the walls of clefts in igneous rocks, in pegmatite veins and associated with metallic com- pounds in ore veins. It is found in many ore deposits of pneumatolytic ongin, notably at Andreasberg in the Harz Mts , at Markirch, in Alsace, in the Seisser Alps, in Tyrol, in the Serra dei Zanchetti in the Bolognese Apennines, at Arendal, Norway, and at many other places In North Amenca it occurs at Deerfield, Mass , at Tariffville, Conn , at Bergen Hill, N J , and at several points in the copper districts of the Lake Superior region
Gadolinite (Be2Fe(YO)2(Si04)2)
Gadolmite is a rather rare mineral with a composition that is not well established Its occurrence is limited to coarse granite veins or dikes — pegmatites — of which it is sometimes a constituent.
Its theoretical composition is as follows, on the assumption that it is analogous to that of datolite
810=2556, Y203=4844, FeO=iS32; BeO=io68 Total=ioooo, but nearly all specimens contain cermm oxides. Others contain nota- ble quantities of erbium or lanthanum oxides and small quantities of thorium oxide Nearly all show the presence of Fe20s, AfeOs, CaO and MgO, and m some helium has been found
The mineral is found massive and in rough crystals with an axial ratio a : b : 6273 : i : i 3215 0=89° 26'. The crystals show comparatively few forms, of which ooP(no), oP(ooi), P£>(on),
336 Descriptive Mineralogy
JPob(oi2), P(Tn) and — P(in) are the most common The> are usually columnar in habit and are lough and coarse The angle iioA 110=64° 12'
Gadolmite is usually black or greenish black and opaque or trans- lucent, but very thm splinters of fresh specimens are translucent or transparent in green tints Its luster is glassy or resinous, streak greenish gray and fracture conchoidal Its hardness is 6-7 and its density about 4-4 5 Upon heating the density increases Many crys- tals appear to be made up of isotropic and amsotropic substance, and some to consist entirely of isotropic matter This phenomenon has been explained in a number of different ways, but no one is entirely satis- factory. In general, the isotropic material is believed to be an amor- phous alteration form of the amsotropic variety It may be changed into the amsotropic form by heating
The crystallized gadolmite swells up m the blowpipe flame without becoming fused and retains its transparency The amorphous variety also swells without melting, but yields a grayish green translucent mass The mineral phosphoresces when heated to a temperature between that of melting zinc and silver. After phosphorescing it is unattacked by hydrochloric acid Before heating it gelatinizes with the same reagent The mineral is weakly radioactive
Localities and, Origin — Gadolmite occurs in the pegmatites of Ytterby near Stockholm, and of Fahlun, Sweden, on the Island of Hittero, in southern Norway, in the Radauthal, in Harz, at Barringer Hill, Llano Co , Texas, as nodular masses and large rough crystals, and at Devil's Head, Douglas Co, Colo In the last locality it occurs in a de- composed granite as a black isotropic variety with a very complex composition Specimens analyzed as follows
I H
Si02 22 13 21 86
Th02 89 81
AbOs 2 34 54
Fe20a i 13 3 S9
ii 10 6 87
(La Di)20a 21 23 19 10
Y20g . 9 50 12 63
ErgOs . , ,. 12.74 15 80
FeO 10 43
BeO 7 19
CaO 34
H20 . 86
Other 60
Total , , 100 48 100 02
It has apparently in some cases solidified from an igneous magma. In others it is of pneumatolytic origin
Anhydrous Orthosilicates
StauroUte (Fe(AlOH)(A10)4(Si04)2)
Staurolite is a mineral that is interesting from the fact that it fre- quently forms twinned crystals that resemble a cross in shape, and which consequently, during the Middle Ages, was held in great veneration Its composition is not well established The composition indicated by the formula above is as shown in the first line below (I) Three analyses are quoted in the next three lines
A1203
Fe203
FeO
MgO
H20
Q 13
Total 100 oo loo 33
SiOo A1203 Fe203 FeO MgO H20 Ti02
Ii 27 38
Hi 30 23
Iv 27 91
I Theoretical composition
II From Monte Campione, Switzerland
III From Morbihan, France
IV From Chesterfield, Mass
Staurolite crystallizes in the orthorhombic system (bipyramidal class) in simple crystals with the axial ratio 4734 i : 6828 The indi-
Fig 183 Fig 184 Fig 185
FIG 183 — Staurolite Crystal with ooP, no (ni), oopoo, 100 (&), oP, ooi (c) and
P 60,101 (r)
FIG 184 — Staurohte Crystal Twinned about oo (032) FIG 185 —Staurolite Crystal Twinned about (232)
vidual crystals are usually bounded by oo P(no), oo P 65 (ooi), P 55 (101) and often oP(ooi), but all their faces are rough (Fig 183) The angle 1 10 A i io =50° 40' More common, however, than the simple crystals are interpenetration twins The most common of these are of two kinds, (i) with f P 06 (032) the twinning plane (Fig 184), and (2) with |P|(232) the twinning plane (Fig. 185) Both types of twins yield crosses, but the arms of the first type are perpendicular to one another and those of
338 Descriptive Mineralogy
the second type make angles of about 60° and 120° Sometimes the twinning is repeated, giving rise to trillings
The mineral is reddish or blackish brown, and has a glassy or greasy luster. Its streak is white It is slightly translucent in fresh crystals, but usually is opaque In very thin pieces it is pleochroic in hyacinth- red and golden yellow tints Its cleavage is distinct parallel to oo P 06 (oio) and indistinct parallel to ooP(no) Its fracture is conchoidal, its hardness 7 and its density 34~38 For yellow light, QJ=I 736, /3=i 741, i 746
Before the blowpipe staurohte is infusible, unless it contains man- ganese, in which case it fuses to a black magnetic glass It is only slightly attacked by sulphuric acid
It is distinguished from other minerals by its crystallization, m- fusibility and hardness
Staurolite weathers fairly readily into micaceous minerals, such as chlorite (p 428) and muscovite (p. 355)
Synthesis — It has not been produced in the laboratory
Occurrence — The mineral occurs principal!} m mica schist and other schistose rocks where it is the result of regional or contact metamor- phism Because of its method of occurrence it frequently contains numerous mineral inclusions, among them garnet and mica
Localities — Good crystals of staurohte are found in the schists at Mte Campione, Switzerland, in the Zillerthal, Tyrol, at Aschaff en- burg, in Bavana, at various places in Brittany, France, and in the United States, at Wmdham, Maine, at Francoma, N H , at Chester- field, Mass , in Patrick Co , Va , and m Fannm Co , N C
Uses — Twins of staurohte are used, to a slight extent, as jewelry. Specimens from Patrick Co , Virginia, are mounted and worn as charms under the name of " Fairy Stones."
Dumortierite (Al(AlO)7H(BO)(SiOi)3)
Dumortierite is one of the few blue silicates known It is a borosili- cate with a composition approaching the formula indicated above The analysis of a sample from Clip, Arizona, gave (I)
SiO2 AbOs Fe203 TiOa MgO B203 P20r> Lossonlgn Total
I. 27 99 64 49 tr 4 95 20 i 72 99 35
II. 28 58 63 31 21 i 49 5 2i r 53 ioo 33
Specimens from California (II) contain in addition notable quantities of TiCfe, which is thought to exist as Ti203 replacing a part of the AkOa.
Anhydrous Orthosilicates 339
The mineral crystallizes in the orthorhombic s>stem in aggregates of fibers, needles or very thin prisms exhibiting only ooP(no) and oo P oo (100) without end faces Its axial ratio is a . 5317 : i, and the prismatic angle no A 110=56° Its crystals possess a distinct cleavage parallel to oo P 66 (100) and a fracture perpendicular to the long axes of the prisms Twinning is common, ith ooP(no) the twinning plane
Dumortierite is commonly some shade of blue, but in some cases is green, lavender, white, or colorless It is translucent or transparent and strongly pleochroic, being colorless and red, purple or blue Its streak is light blue Hardness is 7 and density 3 3 Its refractive indices for yellow light are r 678, /3= i 686, i 089
Before the blowpipe the mineral loses its color and is infusible. It is insoluble m acids
It is distinguished from other blue silicates by its fibrous or columnar character and its insolubility m acids
Its principal alteration products are kaolin and damourite (pp 404, 357)
Occurrence and Locates — Dumortierite occurs only as a constit- uent of gneisses and pegmatites It is found in pegmatite near Lyons, France, near Schmiedeberg, m Silesia, at Harlem, N Y, in a granular quartz, at Clip, Yuma Co , Ariz , and in a dike rock composed of quartz and dumortiente, near Dehesa, San Diego Co , Cal It is evidently a pneumatolytic mineral Its common associates are kyamte, anda- lusite or sillimanite
Sodalite Group
The sodahte group includes a series of isometric minerals that may be regarded as compounds of silicates with a sulphate, a sulphide or a chlor- ide, or, perhaps better, as silicates in which are present radicals con- taining Cl, SO4 and S The minerals comprising the group are hauymte, nosean, sodalite and lasnnte* Of these, sodahte appears to be a mixture of 3NaAlSiO4 and NaCl, in which the Cl has combined with one atom of Al, thus Na4(ClAl)Al2(SiC>4)3 The other members of the group are comparable with this on the assumption that the Cl atom is replaced by the radicals NaS04, and NaSa It is possible, however, that all are molecular compounds as indicated by the second set of formulas given below. All are essentially sodium salts, except that in typical haiiynite a portion of the Na is replaced by Ca. The chemical symbols of the four minerals with the calculated percentages of silica, alumina and soda corresponding to their formulas are:
Descriptive Mineralogy
Si02 A1203 Na20 37 14 31 60 25 60
31 65 27 03 27 26
Sodalite Na4(Cl Al) Al2(Si04)3, or
3NaAlSi04 NaCl Noselite Na4(NaSQi Al)Al2(Si04)3, 01
3NaAlSi04 Na2S04 Hauymte (Na2Ca)2(NaSOrAl)Ab(SiO1)3, or 3199 2732 16.53
3NaAlSi04 CaSO4
Lasurxte Na4(NaS3 Al) A12 (8104)3, or 31,7 26,9 27.3
Na2S
Sodalite
A1)A12 (8104)3)
Sodalite, theoretically, is the pure sodium compound corresponding to the composition indicated by the formula given above Natural crystals, however, usually contain a little potassium in place of some of the sodium and often some calcium, as indicated by the analyses of material from Montreal, Canada (I), and Litchfield, Maine (II), quoted below Moreover, their content of Cl is not constant
Si02 A1203 Na20 K2OCaO Cl C1O Total
I 3752 3*38 2515 78 35 691 - 10209 -155 10054
Ii 3733 3187 2456 10 . 683 10176* -154 10022
Includes I 07 per cent H20
Sodalite occurs massive and in crystals that appear to be holohedral, but etch figures indicate that they are probably tetrahedrally hemi- hedral (hextetrahedral class) Most crystals are dodecahedral m habit, though some are tetrahexahedral and others octahedral The forms usually developed are ooO(no), ooQoo (100), 0(iu), 202(112) and 404(114). Interpenetration twins of two dodecahedrons are common, with 0 the twinning plane (Fig 186) These often possess an hexagonal habit, The mineral is colorless, white or some light shade of blue or red, and its streak is white Its luster is vitreous It is trans- parent, translucent and sometimes opaque Its cleavage is perfect parallel to ooO(no)
and its fracture conchoidal Its hardness is 5-5,6, and its density 2 3. Its refractive index for yellow light, 14827 Some specimens are distinctly fluorescent and phosphorescent.
FIG 186— Sodalite Inter- penetration Twin of Two Dodecahedrons Elon- gated in the Direction of an Octahedral Axis and Twinned about 0(m)
Anhydrous Orthosilicates 341
Before the blowpipe, colored varieties bleach and all varieties swell and fuse readily to a colorless blebby glass The mineral dissolves com- pletely in strong acids and yields gelatinous silica, especially after heat- ing When dissolved in dilute nitric acid its solution yields a chlorine precipitate with siher nitrate Its powder becomes bro\\n on treatment with AgNOs, in consequence of the production of AgCl
The mineral is best distinguished from other similarly appearing minerals by the production of gelatinous silica with acids and the reac- tion for chlorine
As a result of weathering sodahte loses Cl and Na and gams water Its commonest alteration products are zeolites (p 445), kaolin (p 440), and muscovite (p 355)
Syntheses — It has been produced artificially by dissolving nepheline ponder in fused sodium chloride, and by decomposing muscovite with sodium hydroxide and NaCl at a temperature of 500° C
Occurrence and Ortgm — Sodahte occurs principally as a constituent of igneous rocks rich in alkalies and as crystals on the walls of pores in some lavas It is also known as an alteration product of nephehne
Localities — Good crystals are found in nepheline syenite at Ditro, in Hungary, in the lavas of Mte Somma, Italy, in the pegmatites of southern Norway; and at many other points where nephehne rocks occur In North America it is abundant in the rocks at Brome, near Montreal, in the Crazy Mts , Montana, and at Litchfield, Maine The material at the last-named locality is light blue
Noselite and Haiiymte ((NaCaHNaSCX Al)Al2(Si04)3)
Noselite, or nosean, and hauynite, or hauyn, consist of isomorphous mixtures of sodium and calcium molecules of the general formula given above Those mixtures containing a small quantity of calcium are usually called nosean, while those with larger amounts constitute hauyn. The theoretical nosean and hauyn molecules are indicated on p 340 The theoretical compositions of the pure nosean molecule (I) and of the most common hauyn mixture (II) are as follows
SiO2 A1203 Fe203 CaO Na20 Ka20 S03 H20 Total
I 31 65 27 03 27 26 14 06 100 oo
II 31 99 27 32 9 94 16 53 14 22 100 oo
HI 35 99 29 41 31 21 20 91 10 58 i 63 99 61
Iv 33 78 27 42 10 08 13 26 3 23 12 31 . 100 08
Contains also 57 per cent Cl
342 Descriptive Mineralogy
In line III is the analysis of a blue nosean from Siderao, Cape Verde, and in line IV, the analysis of a blue haiiyn from the lava of Monte Vul- ture, near Melfi, Italy
Nosean and hauyn are isomorphous with sodalite They crystallize is the isometric system in simple combinations with a dodecahedral habit The principal forms observed aie ooO(no), ooOoo(ioo) 0002(102), 0(in) and 202(112) Contact and mterpcnetration twins are common, with 0(m) the twinning plane The twins are often columnar.
The minerals have a glassy or greasy luster, are transparent or trans- lucent, have a distinct cleavage parallel to ooQ(iio) and an uneven or conchoidal fracture Their hardness is 5 6 and density 2 25 to 2 5, the value increasing with the amount of CaO present Nosean is generally gray and hauyn blue, but both minerals may possess almost any color, from -white through light green and blue tints to black Red colors are rare The streaks of both minerals are colorless, or bluish For yel- low, light #=14890 to i 5038, increasing with increase m the Ca present Both minerals are fluorescent and phosphorescent.
Before the blowpipe both minerals fuse with difficulty to a blebby white glass, the blue hauyn retaining its color until a high temperature is reached In this respect it differs from blue sodalite which bleaches at comparatively low temperatures Upon treatment with hot water both minerals yield NaaS04 They are decomposed with acids yielding gelatinous silica The powders of both minerals react alkaline Both also give the sulphur reaction with soda on charcoal
The minerals are easily distinguished from all others by their crys- tallization, gelatmization with acids and reaction for sulphur.
Both minerals upon weathering yield kaolin or zeolites and calcite
Synthesis — Crystals of nosehte have been made by melting together Na2C03, kaolmite and a large excess of Na2SO*
Occurrence — Hauyn and nosean occur in many rocks containing nephehne, especially those of volcanic origin and m a few metamorphic rocks. Hauyn is so common m some of them as to constitute an essen- tial component
Localities — Both minerals are found in good crystals in metamor- phosed inclusions in the volcanic rocks of the Lake Laach region, in Prussia, also in the rocks of the Kaiserstuhl, m Baden, in those of the Albanian Hills, in Italy, and at S. Antao in Cape Verde In America haiiyn has been reported from the nephelme rocks of the Crazy Mts,, Montana,
Anhydrous Orthosilicates 343
Lasunte (Na4(NaS3- Al)Al2(Si04)3)
Lasunte is better known as lapis lazuli It is bright blue in color and was formerly much used as a gem stone The material utilized for gem purposes is usually a mixture of different minerals, but its blue color is given it by a substance with a composition corresponding to the formula indicated above Since the artificial ultramarine, which is ground and used as a pigment, also has this composition, the molecule is sometimes represented by the shortened symbol USs, or if it contains but two atoms of S, by the symbol US2 The deep blue lasunte from Asia contains as its coloring material a substance with a composition that may be represented by 15 7 molecules of USs, 76 9 molecules of hauyn and 7 4 molecules of sodahte, corresponding to the percentages.
SiO2 A1203 CaO Na20 K20
32 52 27 61 6 47 19 45 28
S03 S Cl Total (Less C1 O)
10 46 2 71 47 99 97 99 42
Lasunte is thus the name given to the blue coloring matter of lapis lazuli, which is a mixture It apparently crystallizes in dodecahedrons Its streak is blue, its cleavage is dodecahedral, its hardness about 5 and its specific gravity about 2 4 Before the blowpipe it fuses to a white glass Its powder bleaches rapidly in hydrochloric acid, decomposes with the production of gelatinous silica and yields H2S.
It is distinguished from blue sodalite and hauyn by the reaction with HC1, especially by the evolution of H2S
Occurrence — Lasunte is principally a contact mineral in limestone.
Localities — Good lapis lazuli occurs at the end of Lake Baikal, in Siberia, in the Andes of Ovalle, in Chile, in the limestone inclusions in the lavas of Vesuvius, and in the Albanian Mts , Italy
Uses — Lapis lazuli is used as an ornamental stone in the manufacture of vases, and various ornaments, in the manufacture of mosaics, and as a pigment, when ground, under the name ultramarine Most of tfre ultra- marine at present in use, however, is artificially prepared,
ACID ORTHOSILICATES Prehaite (H2Ca2Al2(SiO4)3)
Prehmte is nearly always found in crystals, though it occurs also in stalactitic and granular masses
The theoretical composition of the pure mineral is 8102=43.69,
344 Descriptive Mineralogy
A1203=>2478, CaO=27i6, and H2O 437 Most crystals, however, contain small quantities of FeoOj and other constituents
SiQ. AUOi I'cjOj KO CaO M0 II.O Total
Jordansmuhl, Silesia 44" 26 °° Al 2° tr 49* 10090
Cornwall, Penn 4Q 20 88 5 54 27 ti 4 or 99 85
Chlorastrohte, Isle Royale 37 41 H 02 2 21 i 81 22 20 3 46 7 72 99 75*
Also 32 per cent NaO
Its crystallization is orthoihomhic and hcraimoiphic (rhombic py- ramidal class), with a b 8420 i i 1272 The crystals vary widely in habit, but they contain comparatively few foinis The most prominent are oP(ooi), ooP(uo), 6P(o6i), 2P(32i) and 6P(66i)
(Fig 187) The angle noAiTo=8o° 12' Because they exhibit pyroelectnc l>olanty in the direction of the a a.xis the
crvstals arc thought to be twins, with FIG 187 — Prehnite Crystal with / N . , , .
OOP/XXO W, OOP/, I0o Wl (I*) as the twinning plane JP56, 304 (n), JP55, 308 W Cleavage is good parallel to oP(oor) and oP, ooi (c) The crystals are frequently tabular
parallel to oP(ooi), although other
habits are also common Isolated individuals are rare, usually many are grouped together into knotty or warty aggregates
Prehnite is colorless or light green, and transparent or trans- lucent, and it has a colorless streak Its luster is pearly on oP(ooi) but glassy on other faces Its fracture is uneven, its hardness 7+ and its density 2.80-2 95. For yellow light, i 616, i 626, 7 1 649
Before the blowpipe prehnite exfoliates, bleaches and melts to a yellowish enamel At a high temperature it yields water Its powder is strongly alkaline. It is partially decomposed by strong hydrochloric acid with the production of pulverulent silica. After fusion it dissolves readily in this acid yielding gelatinous silica
The mineral has not been produced artificially
Occurrence — Prehnite occurs as crystals implanted on the walls of clefts in siliceous rocks, in the gas cavities in lavas, and in the gangue of certain ores, especially copper ores It is found also as pseudomorphs after analcite (p 438), laumomte (p 451), and xutrohte (p 454) In all cases it is probably a secondary product
Localities — Fine crystals come from veins at Harzburg, in Thuringia, at Stnegau and Jordansmuhl, Silesia, and at Fassa and other places in Tyrol. Good crystals are found also in the Campsie Hills in Scotland. The mineral is abundant in veins with copper along the north shore of
Anhydrous Orthosilicates 345
Lake Superior and on Keweenaw Point, and it occurs also at Farmington, Conn , Bergen Hill, N J , and Cornwall, Penn
Uses — The mineral known as chlorastrolite is probably an impure prehnite. It is found on the beaches of Isle Royale and the north shore of Lake Superior as little pebbles composed of stellar and radial bunches of bluish green fibers The pebbles were originally the fillings of gas cavities in old lavas The> are polished and used, to a slight extent, as gem-stones About $2,000 worth were sold in 1911 and §350 orth in
Axinite (H(Ca-Fe-Mn)3Al2B(SiO4)4)
Axmite is especially noteworthy for its richness in crystal forms The mineral is a complicated borosihcate for which the formula given above is merely suggestive Analyses of crystals from different localities vary so widely that no satisfactory simple formula has been proposed for the mineral Four recent analyses are quoted below
Radauthal Stnegau Oisans Cornwall
Si02 39 26 42 02 41 53 42 10
A12O3
FeoOs
FeO
MnO
CaO
MgO
H2O
4 gi
£ Oo
3 9°
65S
Total 100 62 ico ii 100 32 100 66
Axinite crystallizes in the trichmc system (pinacoidal class), with a : b : 4921 . i : 4797 and 01=82 ° 54', 0=91° 52', 7=i3l0 32'- The crystals are extremely varied m habit but nearly all are somewhat tabular parallel to 'P(iTi), oo P'(iio) or oo 'P(iTo) About 45 forms have been observed In addition to the three mentioned, 2'?' So (201), P'(III), /P(iFi), 2yP' 06 (021), oo P 06 (oio) and oo P oo (100) are the most frequently met with (Figs 188, 189) The plane 'P(iTi) is usually striated parallel to its intersection with oo 'P(iTo) The angle 100 A i "10 15° 34'. The cleavage is indistinct parallel to ooP'(no) and the crystals are strongly pyro electric
Axinite is brownish, gray, green, bluish or pink, and is strongly pleo- chroic in pearl-gray, olive-green and cinnamon-brown tints It is
346 Descriptive Mineralogy
transparent or translucent and has a glassy luster and a colorless streak Its fracture is conchoidal or uneven It is brittle, has a hardness of 6-7 and a density of 3 3 For red light, i 6720, /3= i 6779, 7 1 6810
Axmite, before the blowpipe, exfoliates and fuses to a dark green glass which becomes black in the oxidizing flame It colors the flame green, especially upon the addition of KHS04 and CaFo to its powder Its powder reacts alkaline It is only slightly attacked by acids. After
Fig 188 Fig 189
FIG 188— Aximte Crystal with ooPoo, TOO (a), 2'P'So, 201 (s), ooP/, no (m),
oo /p ilo (M), P', m and 'P, ill (r) FIG 189 — Axmite Crystal with M , m, a, r and 5 as m Fig 188 Also ooPoo,
oio (6), aP' w , 021 (v), yP, In (e), |,P3, 132 (0), 4/P, 241 (o), 3/P3, 131 (I'),
00 /'PI. 130 (w), 3'P3, i3i and 4'?% 241 (<J).
fusion, however, it dissolves readily with the production of gelatinous silica
The mineral is easily characterized by its crystallization and the green color it imparts to the flame
It has not been produced artificially
Pseudormorphs of chlorite after axroite have been found in Dart- moor, England
Occurrence — Axmite crystals occur in cracks in old siliceous rocks. It is found also in ore veins and as a component of a contact rock com- posed mainly of augite, hornblende and quartz, occuning near the peripheries of granite and diabase masses. It was formed by the aid of pneumatolytic processes
Localities — Excellent crystals of axmite are found at Andreasberg and other places in the Harz Mts , near Stnegau, m Silesia, near Poloma, in Hungary, at the Piz Valatscha, in Switzerland, near Verms and at other points m Dauphme, France, at Botallak, Cornwall, Eng- land, at Komgsberg, Norway, Nordmark, Sweden; Lake Onega, and Miask, Russia, at Wales in Maine and at South Bethlehem, Penn.
Anhydrous Orthosilicates 347
Dioptase (H2CuSiO4)
Dioptase is especially interesting because of its crystallization, which is rhombohedral tetartohedral (trigonal rhombohedral class) Its crys- tals are columnar Their axial ratio is i 5342 They are usually
bounded by oo P2(ii2o), - 2R(o22i) or R(ioYi) and - (1341) or
H - (3141) (a rhombohedron of the third order, Fig 190) Besides
occurring as crystals the mineral is found also massive and in crystalline aggregates.
The composition expressed by the formula given above is 8102—3818, CuO=504o; H20=n 44, which is approached very closely by some analyses. The same composition may be expressed by CuSiOs HaO Indeed, recent work indicates that the mineral is a hydrated metasilicate and not an acid orthosihcate FIG 190 —Dioptase Ciys-
Dioptase has an emerald-green or blackish tai °°P2 "20 and green color, a glassy luster and a green streak °221 mtl[L a It is transparent or translucent, is brittle and its fracture is uneven or conchoidal Its stnations hardness is 5 and its density 3 05. It is weakly
pleochroic and is distinctly pyroelectnc For yellow light, co=i 6580, 6=17079
Before tie blowpipe dioptase turns black and colors the flame green. On charcoal it turns black in the oxidizing flame and red m the reducing flame without fusing It is decomposed by acids with the production of gelatinous silica
Synthesis — Crystals of dioptase have been made by allowing mix- tures of copper nitrate and potassium silicate to diffuse through a sheet of parchment paper
Occurrence and Localities — The mineral occurs in druses on quartz in clefts in limestone, and in gold-bearing placers in the Altyn-Tube Mt. near the Altyn Ssu River, m Siberia, in crystals on wulfemte and cala- mme and embedded in clay near R6zbanya, Hungary, with quartz and chrysocolla in the Mmdonli Mine, French Congo, in copper mines at Capiapo, Chile, and in Peru, at the Bon Ton Mines, Graham Co , Ariz , and near Riverside, Pinal Co,, in the same State. In the Bon Ton Mines it covers the walls of cavities in the ore, which consists of a mixture of kmomte and copper oxides
Descriptive Mineralogy
Mica Group
The mica group comprises a series of silicates that are characterized by such perfect cleavages that extremely thin lamellae may be split from them with surfaces that are perfectly smooth. The lamellae are elastic and in this respect the members of the group are different from other minerals that possess an almost equally perfect cleavage Some of the micas are of great economic importance, but most of them have found little use in the arts
The micas may be divided into four subgroups, (T) the magnesium- iron micas, (2) the calcium micas, (3) the kthium-iron micas, and (4) the alkali micas Of the latter there are three subdivisions, (a) the lithia micas, (£) the potash micas, and (c) the soda micas
All the micas crystallize in the monoclmic system (monoclmic pris- matic class), in crystals with an orthorhombic or hexagonal habit
In composition the micas are complex The alkali micas are ap- parently acid orthosihcates of aluminium and an alkali — the potash mica being KHaAk (8104)3 Other alkali micas are more acid, and some of the magnesium-iron micas are very complex The members with the best established compositions are apparently salts of orthosilicic
acid, and, hence, the entire group is placed with the orthosihcates
All the micas possess also, in addition to the very noticeable cleavage which yields the characteristically thin lamellae that are so well known, other planes of parting which are well exhibited by the rays of the percussion figure (Fig, 191) The largest ra}— known as the characteristic ray — is always parallel to the chnopinacoid. In some micas the plane of the optical axes is the chnopinacoid and m others is perpendicular thereto In the latter, known as micas of the first order, the plane of
the axes is perpendicular to the characteristic ray and m the former, distinguished as micas of the second order, it is parallel to this ray.
The value of the optical angle varies widely In the magnesia micas it is between o° and 15°, in the calcium micas between 100° and 120°, and in the other micas between 55° and 75° When the angle becomes zero the mineral is apparently umaxial But etch figures on all micas indicate a monoclmic symmetry (compaie Fig 194)
FIG 191 — Percussion Figure on Basal Plane of Mica The long ray is parallel to oo Pob (oio)
Anpiydrous Orthosilicates
The Magnesium-Iron Micas
Biotite ((K H)2(Mg Fe)2(Al Fe)2(Si04)3)
The magnesium-iron micas are usually designated as biotite. group includes micas of both orders as follows
This
isl Order Anomite
2d Oraer Meroocene Lepidomelane PUogopiU
The crystals of biotite have an axial ratio 5774 i : 3 2904 with 90° They are usually simple combinations of oP(ooi), oo P ob (oio), |P(ii2) and P(Tn) (Fig 192). Twins are common, with the twinning plane perpendic- ular to oP(ooi) The composition face may be the same as the twinning plane or it may be 193)
witu oP, ooi (c), ooPSb, oio (6), P, In (ju) and -JP 112
oP(ooi) (Fig 193) The crystals have an
hexagonal habit, the angle IiiAoio being FlG ystel
60° 22!'. The mineral also occurs in flat
scales and in scaly aggregates
The color of biotites varies from yellow, through green and brown to black Pleochroism is strong in sections perpendicular to the perfect cleavage, ie, perpendicular to oP(ooi) The streak of all varieties is white Their hardness =2.5 and density 27-3.1, depending upon composition. The refractive indices for yellow
FIG. 193 — Biotite Twinned about a Plane Perpendicular to oP (ooi), and Parallel to the Edge Between oP(ooi) and — aP(22i) The composition plane is oP(ooi) Mica law A= hand twin, B and C-left hand twins.
light m a light brown biotite from Vesuvius are' a— 1.5412, /3=i 5745. They are higher m darker varieties.
Etch figures are produced by the action of hot concentrated sulphuric acid,
Varieties and their Localities — Anomite is rare. It occurs at Green- wood Furnace, Orange Co , Y., and at Lake Baikal, m Siberia
350 Descriptive Mineralogy
Meroxene is the name given to the common biotite of the 2d order It occurs m particularly fine crystals in the limestone blocks included in the lava of Mte Somma, Naples, Italy, at various points in Switzer- land, Austria and Hungary, and at many other points abroad and in this country
Lepidomelane is a black meroxene characterized by the presence in it of large quantities of ferric iron It is essentially a magnesium-free biotite It occurs in igneous rocks, especially those rich in alkalies Two of its best known occurrences in the United States are in the nephe- hne syenite at Litchfield, Maine, and in a pegmatite in the northern part of Baltimore, Md
Phlogopite, or amber mica, is the nearly pure magnesium biotite which by most mineralogists is regarded as a distinct mineral, partly because m nearly all cases it contains fluorine Its color is yellowish brown, brownish red, brownish yellow, green or white Its luster is often pearly, and it frequently exhibits astensm in consequence of the presence of inclusions of acicular crystals of rutile or tourmaline arranged along the rays of the pressure figure Its axial angle is small, increasing with increase of iron Its refractive indices are a=i 562, £=i 606, 7=1 606
Phlogopite is especially characteristic of metamorphosed limestones It occurs abundantly in the metamorphosed limestones around Easton, Pa , at Edwards, St Lawrence Co , N Y , and at South Burgess, Ontario, Canada. It is also found as a pyrogenetic mineral in certain basic igneous rocks,
Typical analyses of the four varieties of biotite follow.
Si02 Ti02 A1203
n
Hi
tr
17 co
s 92
I. 2O
FeO
MnO.
CaO i 48
BaO 33 62
MgO 21 08 9 68 89 26 49
Na20 i 55 45 7 oo 60
Anhydrous Orthosilicates 351
I Ii Iii Iv
K20 9 01 8 20 6 40 9 97
H20- 90 I , 66
H20+ I219 3*6 I*6' 233
F 10 2 24
(lessO=F) 99 19 99 91 100 83 99 66
I Anomite from Greenwood Furnace, Orange Co , N Y
II Meroxene from granite, Butte, Mont
III Lepidomelane from eleohte syenite Litchfield, Maine
IV Brown phlogopite from Burgess, Can
Before the blowpipe the dark, ferruginous varieties fuse easily to a black glass, the lighter colored varieties with greater difficulty to a yellow glass Their powder reactions are strongly alkaline The minerals are not attacked by HC1 but are decomposed by strong EfeSO* In the closed tube all varieties give a little water
The biotitcs are distinguished from all other minerals except the other micas by perfect cleavage and from other micas by their color, solubility in strong sulphuric acid and pleochroism
The commoner alteration products of biotite are a hydrated biotite, chlorite (p 428), epidote, sillimamte and magnetite, if the mica is ferriferous At the same time there is often a separation of quartz Phlogopite alters to a hydrophlogopite and to penmnite (p. 429), and talc (p 401)
Syntheses —The biotites are common products of smelting operations. They have been made by fusing silicates of the proper composition with sodium and magnesium fluorides
Occurrences and Origin — The biotites are common constituents of igneous and metamorphic rocks and pegmatite dikes They also are common alteration products of certain silicates, such as hornblende and augite They are present m sedimentary rocks principally as the products of weathering
Uses — Phlogopite is used as an insulator in electrical appliances and to a less extent for the same purposes as those for which ground muscovite is employed No "amber mica" is produced in the United States Most of that used in this country is imported from Canada.
352 Descriptive Mineralogy
The Calcium Micas
Margante (Ca(AlO)2(AlOH)2(SiO4)2)
Margante, the calcium mica, is like biotite in the habit of its crys- tals, which, however, are not so well formed as these Usually the min- eral occurs in tabular plates with hexagonal outlines but without side planes It occurs also as scaly aggregates
Analyses of specimens from Gamsville, Ga (I), and Peekslull, N Y (II), gave
Si02 A1203 FeO MgO CaO Na20 H20 Total
I 31 72 50 03 12 ii 57 2 26 4 88 100 58
II 32 73 46 58 5 12 i oo ii 04 4 49 100 96
The mineral has a pearly luster on its basal planes, and a glassy luster on other planes Its color is while, yellowish, or gray and its streak white It is transparent or translucent Its cleavage is not as perfect as in the other micas, and its cleavage plates are less clastic Its hard- ness vanes from 3 to over 4 and its density is 3 It is a mica of the first order
Before the blowpipe it swells, but fuses with great difficulty It gives water m the closed tube and is attacked by acids
Occurrence — Margante is associated with corundum It is also present in some chlorite schists In all cases it is of mctamorphic origin
Localities — It occurs in the Zillerthal, Tyiol, at Campo Longo, m Switzerland, at the emery localities m the Grecian Archipelago, at the emery mines near Chester, Mass , in schist inclusions in mica dionte at Peekskill, N Y , with corundum at Village Green, Penn , at the Cullakenee Mine, in Clay Co , N. C, and at corundum local- ities in Georgia, Alabama and Virginia
The Lithium-Iron Micas
Zinnwaldite ((Li- K- Na)3FeAl(Al(F- OH))2Si5Oi0)
The pnncipal -iron mica, zmnwaldite, is a very complex mixture that occurs m several forms so well characterized that they have received different names All of them contain lithium, iron and fluorine, but in such different proportions that it has not been possible to ascribe to them any one generally acceptable formula Some of the most im- portant of these varieties have compositions corresponding to the fol- lowing analyses
Anhydrous Ortiiohilk'Ates 353
I It Iii Iv
Si02. 40 19 59 25 s1 46 45 87
22 79 12 57 l6 22 22 $O
19 78 2 21 66
FeO 93 7 66 ii 6r
MnO 2 02 06 i 75
NasO 7 63 95 42
K20 7 49 5 37 I0 65 10 46
Li20 3 06 g 04 4,83 3 28
F 3 99 7 7 44 7 94
Total 99 32 102 ii 102 71 105 48
— 97 64 99 05 99 60 102 15
I Rabenghmmer from Altenberg Saxony Greenish black with greenish gray
streak Sp gr 146-3 IQO
II Polyhlhiomlc from Kangerluarsuk, Greenland White or light green plates Sp gr =281
III Cryophyllitc from Rrxkporl, Mass, Strongly plewhroic green and brown-
ish led crystals Sp gr 2 QOQ Contains also 17 MgO and i 06 HgO
IV Zinnwaldile from Zmnwald, Bohemia. Plates, white, yellow or greenish gray Sp. gr 956-2,087 Contains also r;i IIjO and 08
Zinnwalchle occuis m crystals with u,n axial ratio very near that of biotitc, and a tabular habit Twins arc like those of biotitc with ooP(iio) the twinning plane
It has a pearly luster, is of many colors, particularly violet, gray, yellow, brown and dark gieen and is strongly plcochroic. Its streak is light, Us hardness between 2 and 3 and its density between 2.8 and 3 2. It is a mica of the second 01 der
Before the blowpipe it fuses to a dark, weakly magnetic bead It is attacked by acids
Qccumnte and Lotahtic\ — Zmnwaldite is found m certain ore veins, m granites containing cassiterite, and m pegmatites Its origin is as- cribed to pneumatolytic processes Us principal occuirences are those referred to m connection with the analyses
Tu& Alkali Micas
The alkali micas include those m which the principal metallic con- stituents besides aluminium are lithium, potassium and sodium. All these metals are present in each of the recognized varieties of the alkali micas, but in each variety one of them predominates That in which lithium is prominent is known as lefodolite; that m which potas-
364 Descriptive Mineralogy
sium is most abundant is muscowte, and that in which sodium is most prominent is paragomte Muscovite is common Lepidolite is abundant in a few places Paragomte is rare The first two are im- portant economically All are micas of the first order, except a few iepidolites, and all are light colored
Another mica, which is usually regarded as a distinct variety of muscovite, or, at any rate, as being very closely related to the mineral is roscoelite In this, about two-thirds of the AlgOs m muscovite is replaced by VgOj, It is a rare green mica which is utilized as an ore of vanadium,
Lepidolite ((Li- K-Na)2((Al-Fe)OH)2(SiO,Oa)
Lepidohte occurs almost exclusively as aggregates of thin plates with hexagonal outlines Crystals are so poorly developed that a satis- factory axial ratio has not been determined Its variation m composi- tion is indicated by the analyses of white and purple varieties from American localities
Si02 A1203
12
28 So
undet.
24 ,
Oo
I 34*
°s
Oo
tr
4 9°
S 12
4
T 94
.
5 So
S 18
2 Og
FeO
MnO
MgO
CaO
LiaO
NaaO
KsO
Rb20
CsaO.
F.
BfeO
Total
(lessO=F) 99 45 100 53 99 74 99.63
I. Like-purple granular lepidohte from Rumford, Maine II White variety from Norway, Maine III Red-purple variety from Tourmaline Queen Mine, Pala, Cal. Contains
also 04 PjOj IV. White variety from Pala, Cal
Anhydrous Orthosilicates 355
The mineral is while, rose or light purple, gray or greenish The rose and purple varieties contain a little manganese The streak of all lepidolites is white, their luster pearly, their hardness 2 5-4 and density 28-29 The refractive indices of a typical variety are 0=i 5975* 7 ==16047
Lepidohte fuses easily to a white enamel and at the same time colors the flame red It is difficultly attacked by acids, but after heating is easily decomposed
Cookeitc fiom Maine and California is probably a weathered lepido- hte Its analyses concspond to the foimula, Li(Al(OH)2)3(SiOa)2
Occutrencc — The mincial occuis puncipally in pegmatites in which lubelhte (p 435), and other bi ight-colored tourmalines exist and on the borders of granite masses and in rocks adjacent to them It is often zonally mtergrown with muscovitc In all cases it is probably a pncunutolytic pioduct, or, at least, is produced by the aid of magrnatic emanations
Localities — The mineral occurs in nearly all districts producing tin, and also in those producing gem tourmaline Its best known foreign localities are Jekatcrmbuig, Russia, Rozna, Moravia, Schmttenhofen, Bohemia, and Penig, Sa\ron> In the United States it is found in large quantities at Hebron, Pans, and other points in western Maine, m the tin mines of the southern Black Hills, South Dakota, and in the tourma- line localities m the neighborhood of Pala, San Diego Co , Cal
Usei> — Lepidohte is utilized to a slight extent m the manufacture of lithium compounds, which are employed m the preparation of lithia waters medicinal compounds, salts, used in photography and m the manufacture of fireworks and stoiage batteries
Muscovite (Ha(K Na)Alj(SiOi)a)
Muscovitc is one of the most common, and at the same time the most important, of the micas Because of its transparency it is em- ployed for many purposes for which the darker biotite is not suitable
While predominantly a potash mica, nearly all muscovite contains some soda, due to the isomorphous mixtuie of the paragomte molecule. Two typical analyses are quoted below:
Si02 AlsOs FeaOs FeO MnO MgO CaO NaaO KS0 HaO F Total
I 44 39 35 7° 09 i 07 tr ro 2 41 9 77 5 88 .72 10113
II. 46 54 34 96 i 59 . 32 38 5 43 99 63
I. Broad plates of muscovite bordered by lepidoiite, Auburn, Maine. II Greenish muscovite, Auburn, Maine Total less QF n 100.83
Descriptive Mineralogy
The crystals are usually tabular and frequently orthorhombic or hexagonal in habit, though the etch figures on their basal pines reveal clearly their monoclimc symmetry (Fig 194) If onentated to corre- spond with crystals of biotite their a\ial constants are a b 5774 i . 3 3128, 0=89° 54', and their principal planes oP(ooi), oo p & (Oio) ob (023), 4P(44i) and -2P(22i) (Fig IQS)
Twins like those of biotite are not uncommon in some localities Muscovite is colorless or of some light shade of green, yellow or red It has a glassy luster, a perfect cleavage parallel to the base, a haidness of 2 and a density of 2 76-3 i Pleochroism is marked in dncctions perpendicular and parallel to the cleavage, the color of the crystals, when viewed in the direction perpendicular to the cleavage being lighter
Fig 194
I'll, 1 1)5.
FIG 194 — Etch Figures on oP(ooi) of Muscovite, Exhibiting Monodmu, Symmetry FIG 195 — Muscovite Crystal with — 2P, 221 (Af)t oP, ooi <wPw, oio (/;),
and 023 (r)
than when viewed parallel to the cleavage The optic al angle is com- paratively large (56°-76°), in this respect being vciy different from that of biotite which is small (2°-22°) The mineral is a nonconductor of electricity at ordinary temperatures and a poor conductor of heat. Its refractive indices vary somewhat with composition For yellow light intermediate values are as follows i 5619, j8- 1.5947, 1,6027,
Before the blowpipe thin flakes of muscovite fuse on their edges to a gray mass In the dosed tube the mineral yields water which, in some cases, reacts for fluorine It is insoluble m acids under ordinary coi> ditions, but is decomposed on fusion with alkaline carbonates.
Muscovite is very stable under surface conditions Its principal change is into a partially hydrated substance, which may be culled hydromuscovite. It alters also into scaly chlontic products, into steatite (p 401), and serpentine (p, 398).
Anhydrous Orthosilicates 357
DomounU is a dense fine-grained aggregate of muscovite, often forming pseudomorphs after other minerals
Sencte is a yellowish or greenish muscovite that occurs in thin, curved plates m some schists
Fwhsite is a chromiferous variety of an emerald-green color from Schwarzenstem, Tyiol
Synthesis — Crystals of muscovite have been made by fusing anda- lusite with potassium fluo-sihcate and aluminium fluoride
Occurrence — Muscovite occurs in large, ill-defined crystals in peg- matites, and in smaller flakes in giamtes and othci acid igneous rocks, in some sandstones and slates and m various schists and other meta- morphic rocks It is found also in veins It is m some cases an orig- inal pyrogemc mineral, m other cases a mctamorphic mineral and m still other cases a sccondaiy mineral resulting from the alteration of alkaline aluminous silicates
Localities — The mineral occurs m all regions where pegmatites and acid igneous rocks c\ist It is mined m North Carolina, South Dakota, New Hampshire, Virginia and other states While phlogopitc (amber mica) is produced in some countries all the mica produced in this country is of the muscovite variety
t/iw —Muscovite is used m two forms, (i) as sheet mica, and (2) as ground mica. The sheet mica comprises thm cleavage plates cut into shapes It is used in making gas-lamp chimneys, lamp shades, and windows in stoves. The greater portion is used as insulators m electrical appliances, though for some forms of electrical apparatus the amber mica js better Because of the comparatively high cost of large mica plates, small plates are sometimes built up into larger ones The ground mica consists of small crystals and the waste from the manu- facture of sheet mica giound very fine. It is used in the manufacture of wall paper, heavy lubucants and fancy paints It is also mixed with shellac and melted into desired forms for electrical insulators
Production — The total value of the mica produced in the United Stales during 1912 was $355,804, divided as follows. 1,887,201 Ib sheet mica, valued at $310,254 and 3,512 tons ground mica, valued at $45,550 Of this North Carolina produced 454,653 11), of sheet mica, valued at $187,501 and 2,347 tons of scrap mica, valued at $29,798, or a total value for both kinds of mica of $217,299 The imports of sheet mica during the same year amounted to $502,163, of which 241,124 Ib , valued at $155,686 was trimmed and the balance untnmmed The imports during 1912 were valued at $748,973, and the domestic produc- tion at $331,896-
358 Descriptive Mineralogy
Roscoelite may be regarded as a muscovite in which a large portion of the AkOs has been replaced by V20s A specimen from Lotus, Eldo- rado Co , Cal , gave
Si02 Ti02 A1203 V203 FeO MgO K80 H,0- H,0+ Total 45 17 78 ii 54 24 01 i 60 i 64 10 37 40 4 29 99 80
besides traces of Li20 and Na20
The mineral occurs as clove-brown or green scales with a specific gravity of 2 92-2 94 It is translucent and has a pearly luster and a strong pleochroism. Its refiactive indices for sodium light are, 1,610,
0=1685,7=1 704
Before the blowpipe it fuses to a black glass. It gives the usual reactions for vanadium m the beads and is only slightly alTccted by acids It has been found associated with gold m small veins ncui Lotus, Eldorado Co., California, in seams composed of roscochte and quartz between the beds of a sandstone in the high plateau region of south- western Colorado, and as a cement of minute scales between the grams of the sandstone on both sides of the seams. In all cases it appears to have been deposited by percolating water, possibly of magmatic origin
The impregnated sandstone is mined as a source of vanadium The material, which contains an average of about 3 per cent of metallic vanadium is concentrated by chemical processes, and the concentrates are manufactured into ferro-vanadium. Most of the vanadium pro- duced in the United States is made from this ore,
Paragonite (Na-KJAlsCSiO-Oa)
Paragonite, the sodium mica, differs from muscovite mainly in com- position Both contain sodium and potassium but in puragomte the sodium molecule is in excess
The analysis quoted below is made on a sample from Monte Cam- pione, in Switzerland
Si02 AI203 Fe203 Na20 K20 H20 Total 47 75 40 10 tr. 6 04 i 12 4 58 99 59
It occurs in the same associations as some forms of muscovite but it is much less common. It apparently occurs most abundantly in certain fine-grained mica schists to which the name paragonite schists has been given, It i§ m ail known cases a product of dynamic metamorphism*
CHAPTER XVII THE SILICATES-Cowfowwrf
The Anhydrous Metasilicates
Normal Metasilicates
Beryl (BeaAl2(Si03)o)
BFRYL is a frequent constituent of coarse-grained granites. It is important as a gem matciial, and is particularly interesting because of the many physical investigations that have been made with the aid of its crystals
Although the mineral is essentially a beryllium alummo-rnetasilicate, it usually contains also a little FesOa and MgO, in many cases small quantities of the alkalies, and in some cases also caesium. Analyses of a green beryl from North Carolina, an aquamarine from Stoneham, Me , and a light-colored crystal from Hebron are given below
Si02 AfcOi Fe20;j BeO FeO Na20 Li20 Cs20 H20 Total
I. 66 84 19 05 . 14 n . 100 oo
Ii. 66 28 18 60 . 13 61 ,22 ,, ,. .83 90 54
Iii 65 54 17 75 21 13 73 71 ... 2 01 100 39
IV, 62 44 17,74 40 ii 36 ,38 i 13 I 60 3.60 2.03 100 30
I Theoretical II, Alexander Co,, N. C, II I Stoneham* Me.; ako.o6%CaO. IV, Hebron, Me
The mineral occurs massive without distinct crystal form and also in granular and columnar aggregates, but its usual method of occurrence is in sharp and, in some cases, very large columnar crystals with a distinct hexagonal habit (dihexagonal bipyramidal class), and an axial ratio i : 4989. The forms found on nearly all crystals are oo P(tolo), ooP2(ii2o), oP(oooi), P(ion), P2(ii22) and 2P2(ii2i) (Fig 196), In addition, there are present on many crystals other prismatic forms and the pyramids 3?f (2131) and aP(ao3i). Other crystals are highly
Descriptive Mineralogy
modified (Fig 197), the total number of forms that have been identified approximating 50 The angle icli Aoi7i 28° 55' Some crystals are very large, measuring 2 to 4 feet in length and i ft in diameter
Beryl has a glassy luster It is transparent or translucent It is colorless or of some light shade of green, red, or blue Its streak is white, hardness 7-8 and density 2 6-2 8 Its cleavage is very imperfect but there is frequently a parting parallel to the base Pleochroism is noticeable in green and blue crystals Its refractive indices for yellow light at 20° are co= i 5740, i 5690 They become greater with increas- ing temperature
Before the blowpipe colorless varieties become milky, but others are
FIG tg6 1'ic, 197
FIG 196— Beryl Crystals with °op, ioTo (w), oP oooi (c), P2, 1120 (a), P, loii (p) and 2?2, 1 121 00
FIG 197 — Beryl Crystal with m, c, p and A as m Fig 196 Also 2p, 202 1 (M) and
3Pg, 2131 M
unchanged except at very high temperatures when sharp edges arc fused to a porous glass The mineral is not attacked by acids.
Beryl is distinguished from apatite, which it much resembles, by its greater hardness
It alters to mica and kaolin (p 404)
Syntheses — Beryl crystals have been formed by long heating of 8162, AkOs and BeO m a melt of the molybdate or vanadate of lithium, and by precipitating a solution of beryllium and aluminium sulphates with sodium silicate and heating the dried precipitate with boric acid in a porcelain oven
Occurrence —The mineral occurs as an accessory constituent m peg- matites and granites, in crystalline schists, especially mica schists and
Anhydrous Metasilicates 361
gneisses, m ore veins and sometimes in clay slates and bituminous lime- stones
Uses — The transparent varieties are utilized as gems, under the following names
Emerald is a deep green variety, the color of which is probably due to CroOa,
Aquamarine, a blue-giccn variety,
Golden beryl, a topa/-coloiecl variety,
Blue betvl, a blue vanety, and
White beryl, a coloiless variety
Localities — Crystals of ordinal y ber>l occur at Stnegau, Silesia, in the cassitente veins near Altcnbcrg, in Savony, m the granite dikes near S Piero, Elba, in the Mouine Mts , at Down, Ireland, at various points (especially near Jekatermburg), in Uuil, Russia, and in North America, m the mountain counties of Noith Carolina; at Mt. Antero, Colo ; at Peiperville, , in giamte veins at Haddam, Conn., at Acworth, N H , and at Norway, Hebron, and other points in western Maine Much of the beryl of Maine is the variety containing caesium.
The finest emeralds are found in geodes, and embedded in a clay slate at the Muso Mine, Colombia, New Grenada, but fine gem mate- rial occurs also at Zabara, neat the Red Sea, Habachthal, Tyrol, Glen, New South Wales, and m Bnuil, Hindustan and Ceylon. The finest aquamarines come from Sibeiia,
The most important beryl mines m the United States are m pegma- tites in Cleveland, Burke and Macon Counties, N C Aquamarine, golden beryl and the more usual varieties occur at Walker Knob, Burke Co , and on Whiterock Mt in Macon Co., but those at the first-named locality are not clear enough to furnish gems. Near Clayton, Ga , a pegmatite contains large bliush and yellowish green beryls, some of which yield gem material The finest aquamarine ever found m the United States was from Stoneham, Me. Near Shelby, Clevelaid Co , and at Crabtree Mountain, Mitchell Co , m North Carolina, genuine emeralds occur in a pegmatite that cuts basic rocks. Fine emeralds have also been mined at Stony Point, N C,, Haddam, Conn., and Topsham, Me
Production — The total yield of emerald from North Carolina during 1912 was about 2,969 carats, valued at $12,875 in the rough The average value of the cut stone was $25 per carat, but some especially fine gems from the Shelby locality were valued at $200 per carat There were also produced in the United States during this year other varieties of beryl, valued at $1,765.
362 Descriptive Mineralogy
Leucite (K2Al2(SiO3)4)
Leucite occurs almost exclusively m what are apparently simple isometric crystals, but which are actually polysynthetic twins of a doubly refracting substance At 500° and above, leucite substance is isometric. It separates from molten magmas as isometric crystals, which, upon further cooling, become twinned The twinning is revealed by striation on the crystal faces The substance is, therefore, dimorphous
Theoretically, leucite is a potassium aluminium meUsihcate, but most natural crystals contain some soda and many contain small quan- tities of calcium The calculated composition of the pure molecule and the actual composition of two natural crystals are shown below
Si02 A1203 CaO Na20 K2O HjO Total
Calculated 55 02 23 40 21 58 100 oo
Mt Vesuvius ss 28 24 08 60 20 79 100 75
Mt Vulture 54 94 25 10 i 80 i 23 15 18 2 13 100 38
The mineral occurs in icositetrahedrons, 262(211), m some cases modified by oo 0(no) and oo 0 oo (100) Twinning parallel to oo 0(no) is common, but often the twins are polysynthetic and are recognizable only by stnations on the crystal faces The twinning lamellae are amsotropic, as shown by their optical properties, but at 500° the twin- ning disappears and the crystals become completely isotropic through- out
Leucite is glassy in luster and colorless, white or light gray m color. It is transparent or translucent and has a white streak. Its cleavage is imperfect parallel to oo 0(no), and its fracture is conchoidal or unevtkn. It is brittle Its hardness is 5-6 and density 2 5. Its indices of refrac- tion approximate i 508
Before the blowpipe leucite is infusible It is soluble m HC1 with the production of pulverulent silica Its powdei reacts strongly alka- line
It is distinguished from other minerals by its crystallization, by the violet color it imparts to the flame and its reaction toward HCl, It is most apt to be confused with analcite (p, 458) and colorless garneL It is distinguished from the latter by its inferior hardness and from the former by its mfusibility and failure to yield water when heated in the glass tube below red heat Analcite, moreover, fails to give the flame test for potash
The mineral alters quite readily into analcite and some other zeolite, into a mixture of orthoclase and nepheline, or into orthoclase (p. 413)
Anhydrous Metasilioates
and muscovite, or into orthoclase alone* Its final alteration product is kaolin
Syntheses —Us crystals have been obtained by fusing its constituents, and also by molting a mixture of SiOa, potassium alummate and vana- date, and by fusing a mixtuic of and with an excess of KF
Occurrence —It occurs only in igneous rocks, especially m lavas low in silica and high m potash, and in the plutomc rock known as missourite In some old rocks it is repie&ented by its alteration products. In all cases it is a pimuiy mineral
Localities — Leucite is an essential constituent of the lavas m the Kaiserstuhl, Baden, m Rhenish Prussia, near Wiescnthal, Saxony, in the Sicbcnburgei, Bohemia; at Vesuvius, Italy, m the Leucite Hills, and other places in Wyoming, and at several places in Montana, at Magnet Cove, Ark , and near Hamburg, N J
VMS. — It is suggested that the large masses of leucitc rocks m the
Leucite Hills be used as a source of potash On the assumption that
the rocks at this place contain ro ]>er cent of KO it is estimated that
the total quantity of potash in them amounts to about 200,000,000 tons.
The Amphibolous
The amphibolous embrace a large numbei of minerals, some of which are extremely important as lock components. Economically,
pio
Jio
uo
B
FIG. ig8 — Cross-Sections, of Pyroxene (A) and Amphibolc (#) Crystals* Illustrating Differences in InterseUionb of Cleavage*
they have little value. Several are used iri the arts, but only to a com- paratively slight extent. Apparently they crystallize in the orthorhom- bic, monoclimc and triclmic systems.
The amphiboloids are divisible into two groups, the pyroxenes and the amphiboles, which differ from one another in the ratio between their
364 Descriptive Mineralogy
a and b axes. In the pyroxenes this ratio is nearly i . i, while in the amphiboles it is approximately 2 i The angle between the prismatic planes ( oo P, no) on the former is nearly equal (87° and 93°), and on the latter very unequal (s6°-i24°). Since, moreover, in all members of both groups there is a distinct cleavage paiallel to the unit prism, the angles of intersection of the cleavage planes in the pyroxenes and in the hornblendes are also different This difference m prismatic and cleav- age angles of the two groups serves leadily to distinguish between them (Fig 198)
The pyroxenes appear to be the more stable at high temperatures and the amphiboles under high pressuies Thus pyroxenes are more common than the amphiboles in lavas and amphiboles more common than pyroxenes in crystalline schists
Chemically, the amphiboloids are metasihcates ot Na, Li, Mg, Ca, Fe, Mn, Zn and Al, or isomorphous mixtures of Ihcse metasihcates with one another and with an orthosilicate of the general composition rep- resented by (Mg Fe)((Al Fe)O)3SiQi
THE PYROXENES (R"Si03, R'Al(Si03)2 and RVoVSiO,)
The pyroxenes occur very widely spread as constituents of igneous rocks, and in veins that have been filled by igneous processes. Some members of the group are also common metamorphic pi oducts Although crystallizing in different systems their crystals possess a ccitam family resemblance, expressed best in their hon/ontal cross-sections, which have a nearly orthorhombic symmetry, i e , they uic nearly symmetrical about two planes at right angles to one another, passing through the a and b axes, which are nearly equal The most perfect cleavage of all the pyroxenes is parallel to ooP(no), and consequently their cleavage angles aie nearly equal (Fig I98A) They approximate 92° and 88°, with the plane of the a and c axes (the plane of symmetry in monochnic forms) bisecting the acute angle
The best known members of the series with their axial ratios are listed below In the case of the orthorhombic members it will be noticed that the shorter of the lateral axes is made x This is clone to empha- size the correspondence between the orthorhombic, monoclimc and tri- forms in their axial ratios The usual orientation, that which regards the longer of the lateral axes as 5(=i) gives a : b . c 9702 : i : 5710 for bronzite, and .9713 : i 5700 for hypersthene. By many authors wollastomte and pectolite are placed in an independent
Anhydrous Metasilicates
group partly because of the fact that they are much more easily decom- posed by acids than are the other pyroxenes, and partly because of their very different crystal habits, and different axial ratios
Orthorhombic (possibly twinned monochmc)
MgSiO b a c i oss i 587
(Mg Fe)SiO, =10308 i 5885
Bronzite Hypersthene
Wollaslomtc
Peclohte
Diopside
Sahhte
Hedcnbcrgite
Schejfente
Aiigile
Acmite Aeginnc
fadcitc Spodumene
Rhodonite Bu\tamtte Rabmglonite Fowlente
FcSiOj
1 02QS r 5868
Monoclimc (monochmc prismatic class)
CaSiO,
HNaCa2(Si03)3
(Mg Gi)SiO,
(Mg Fc)Ca(Si08)2
FeCa(SiOn)2
(Mg Fc)(Ca Mn)(SiO,)i r(Mg PeJCXSiCMj I (Mg Fc)((M Fc)0)jSi04 lNd(Al Fc)(biOOa
a b c —i 0523 i 9649 0=8 1140 i 9864 — 10921 i
Na\l(SiO,)j, LiAl(SiO,)>
i OpO
10955
1090-6
S83
=84° 40'
=74° 10'
74° 14'
73° ii' 7?° 09'
Trichnic (trichnic piiucoidal ckiss)
MnSiOi a I '6=1 0729 i 6213 £—108° 44'
(Mn Ca)SiOi
(Ca Fe Mn)jFcfc(SiOOi =10807 i 6237 saio8°34'
(Mn Fc Ca Zi
In addition, there arc several comparatively rare monoclimc pyrox- enes and one trichnic form, that contain zirconium. They occur only as components of rocks rich in alkalies.
Pyroxenes
Enstatite (MgSiOa)— Bronzite— Hypersthene (FeSiO3)
The orthorhombic pyroxenes are isomorphous mixtures of MgSiOa and FeSiOs The pure magnesium and iron molecules are not known in nature, though the former has been produced artificially. Nearly all members of the group contain both magnesium and iron. When the proportion of the iron present is small (5 per cent FeO), the mixture is known as ewtotite Mixtures with 5 to 16,8 per cent of FeO (cor-
Descriptive Mineralogy
responding to MgO . FeO ZX are known as bronzite and mixtures containing more than 16 8 per cent FeO are known as hypersthene The composition of MgSiOs and of some typical members of the group follow
Si02
I 60 03
II 58 oo
HI 55 So
Iv 52 12
A1203 FeO
MgO
CaO HaO
Total 100 oo
99 Si
I Calculated composition of MgSi03 II Portion of large crystals of enstatite from Kjorrestad, Norway
III Calculated composition of upper limit of bronzite, i c , m which MgO FeO
i
IV Hypersthene powder separated from a gabbro at Mt Hope, Md
The three minerals occur in crystals that have a well marked ortho- rhombic symmetry, but it is believed that this may be a case of pseu- dosymmetry only, i e , that the minerals may in reality be monochnic, and that their apparently orthorhombic symmetry may be due to repeated polysynthetic twinning of very thin lamellae. Monochnic MgSiOs has been made by fusion of Si02 and MgO in the presence of B20a, but it is not certain that this is identi- cal with an iron-free enstatite
The natural crystals of the oilhorhombic pyroxenes are columnar in habit and are usually bounded by oo P(no), oo P 06(010), oo P 66(100), P2(2i2), JP 06 (014), with the addition on some crybtals of 001*2(120), 56 (034), P(iii), aP5(an), iP*(o) and other forms (Fig 199) All cleave per- fectly parallel to ooP(uo) with u cleavage angle of 88° i6'-2o' and 91° 4o'~44'* The angle noAiIo=88° 16' to 88° 20'.
The color and other physical properties of the orthorhombic pyroxenes vary with the
amount of iron present Enstatite is light gray, yellow or green. Hypersthene is black, dark purple or dark green Bronzite is brown, or some shade lighter than hypersthene and darker than enstatite. All colored varieties are pleochroic, the difference in color in different directions increasing with the increase in iron Green, red, yellow and brown tints are most prominent. All varieties have a colorless streak.
FIG. 199 — Enstatite Crys- tal with oo P, no (m),
oo Poo, 100 (a), oo Poo, oio (6), co, 023 (q), JPoS, 012 |P5, 016 ($) and |P, 223 (T)
Anhydhouh Metasilicates 367
Many hypcisthencs and bronzites exhibit a metallic shimmer on oo P 06(010), due to tiny inclusions with then flat sides parallel to this direction The hardness of the orthorhombic pyroxenes vanes between 5 and 6 and then density between 3 i and 3 5 increasing with the iron present Their refractive indices for yellow light are
Enstatite a— i 665 /3=i 669 7=1 674
Hypersthene 692 702 705
Before the blowpipe the iron-free members of the series are infusible. With increase m iron they become more easily fusible, very ferruginous hypersthene melting easily to a greenish black weakly magnetic glass When treated with hydrochloric acid the members near enstatite are unattacked, while those near hypersthene are slightly decomposed
Syntheses —Crystals of these pyroxenes have been made by fusing the proper components with BaOj), and by heating mixtures of SiCfe and MgCfe They are frequent constituents of slags
Occurrence — The rhombic pyroxenes occur in igneous rocks, in crys- talline schists, m metamorphosed dolomites and in veins that have been filled by igneous magmas They are not very stable under the condi- tions at the earth's surface They weather to serpentine, hornblende and rarely to talc Enstatite occurs also m meteorites
Locahhe —Good crystals of the orthorhombic pyroxenes are found in the volcanic bombs (inclusions m lava) of the Lake Laach district, Prussia, in oie veins at Bodenmais, Bavaria, at M£, Hungary, m the trachyte of Mont Dore, France, in apatite veins at Snarum, Norway, and in a glassy andesite on Peel Island, Japan In the United States they occur m basic coarse-grained igneous rocks m North Carolina, Maryland, and the Highlands of New York and New Jersey, m volcanic rocks in Colorado, and at the Corundum Mines, m Georgia. Espe- cially fine bronzite occurs on Paul's Island, Labrador.
Monoclinic Pyroxene'S
The monoclinic pyroxenes comprise a series of isomorphous mixtures of monoclinic mctasihcutes of Na, Li, Ca, Mg, Fe" and Mn and the silicate R" (R"'0)a Si04, in which R" is usually Mg, Ca or Fe and R'" is Al or Fe.
.Although their chemical composition vanes quite widely, the crys- tallization of all the members of the group is practically the same With the exception of wollastomte and pectolite the habit of their crystals is similar and their corresponding mterfacial angles have approximately the same value.
368 Descriptive Mineralogy
The group may be subdivided into four subgroups (i) the wollas- tonite subgroup, including this mineral and pectolite, with calcium as the principal metallic component, (2) the magnesmm-calcium-iron pyroxenes, including diopside, sa\hte, lelenbergite and augtte, and (3) the alkali pyroxenes including acm te,jaleite and *po lumene A fourth subgroup includes the rare zirconium-bearing pyroxenes All crystal- lize in the monoclinic prismatic class
WoUastomte Subgroup
These minerals, because their axial ratios are somewhat different from those of the other monoclinic pyroxenes, and because they are much more easily decomposed by acids, are by some mineralogists re- garded as constituting an independent group
Wollastonite (CaSiOs)
WoUastomte analyses correspond very closely to the theoietical composition required by the formula assigned to it There is, however, nearly always a little Fe20a present and usually there arc present also small traces of other constituents A dimorph, pseudowollastonite, 01 /3 wollastomte, has been made by melting wollastomtc and cooling slowly, but it has not yet been found m nature Its crystals arc hexag- agonal or monoclinic with an hexagonal habit
Si02 FeO MnO CaO MgO Na20 H20 Total
Theoretical 51 75 48 25 . 100 oo
Bonaparte Lake, N Y 50 66 07 47 98 05 46 72 99 94
The mineral forms tabular or columnar crystals bounded by oo P 60(100), -Poo(ioi), oP(ooi), P6o(io7), oop2(i2o), -PS(i22)
and oop|(54o) (Fig 200). Twins are sometimes found with oo P 6b (100) the twinning plane The angle 540 A 540 79° 58' The mineral occurs also in granular and fibrous masses Its cleavage is per- v g feet parallel to oo P 06 (100) and only a t a little less perfect parallel to oP(ooi)
a Wollastonite is usually colorless or
TV ™ 11 4. o white, but in some cases is grayish, yellow-
FIG -200 —Wollastonite Crys- -uj-ir i
tal with bPt ooi (c), oo POO, lsh> reddlsh or brown It is transparent
ioo (a), -Poo, ioi or translucent and has a white streak, Its
+P 55 , ioi (/), -hJP PO , luster is glassy except on the cleavage face
102 and oopf, S4o (h) where it is often pearly. Its hardness is
Anhydrous Metasilicates 369
4 5-5 and density 2 8-2 9, and its refractive indices for yellow light are a=i 621, 633, 7=1 636
Befoic the blowpipe wollastonite fuses with difficulty to a white transparent glass Its fusing point vanes between 1240° and 1325°, diminishing with increase in iron It dissolves in HC1, leaving a residue of gelatinous silica, and is attacked vigorously by strong solutions of NaOH When fused it recrystalhzes in hexagonal crystals (pseudo- wollastonite)
The mineral is distinguished from other white silicates by its crys- tallization, its cleavage and its solubility m hydrochloric acid Its prin- cipal alteiation is into apophylhte (p 443)
Syntheses — Ciystals of wollastonite have been made by fusing SiCfe and CaFa, and by dissolving the hexagonal modification (made by fusing and cooling wollastonite) in molten calcium vanadate at 8oo°-9oo°.
Occurrence — Wollastonite is characteristically a product of meta- morpluc pioccsscs, both contact and regional It occurs in metamor- phosed dolomites, in the limestone inclusions in the lava of Vesuvius, etc , in many gneisses and in some eruptive rocks. It is found also abundantly in caltaicous slags
Localities — Crystals of wollastonite aie found in the phonolite of the Kaiberstuhl, ncai Fmburg, Bavaria; m a contact metamorphosed lime- stone neai Cxiklova, Ilungaiy, in the limestone bombs in the lava of Mt, Somma, Naples, Italy, and of Santorm, Greece, and m limestone at Dunn, N Y Granulu or fibrous masses occur also at Attleboro, Penn , at dilTeient points in Lewis, Essev and Warren Counties, N, Y , and at the Cliff Mine, Keweenaw Pt , Mich.
Pectolite (HNaCa2(Si03)3)
Pectolite was formerly regarded as a partially weathered wollastonite Recent analyses, however, indicate that it may have a definite compo- sition which can be represented by the formula written above, as shown by the analyses quoted below The excess of water shown by most analyses is ascribed to the admixture of some weathered material,
SiOs AlaOs MgO CaO NasO K20 EM) Total
I. 54 23 33 72 9 34 .. 2 71 KX> oo
IL 45 32 34 oo 9 32 , 2 55 100 30
III 53 94 71 i 43 32 21 8 57 ,47 4 09 100 82
I Theoretical
IT Niakornat, Greenland Contains also u per cent TTT Point Barrow, Alaska
.370 Descriptive Mineralogy
The mineral usually occurs in fibrous masses of acicular crystals elongated in the direction of the orthoaxis, but in a few cases in tabular forms flattened parallel to oo P oo (100). Its cleavage is distinct parallel to the same plane
Pectohte when pure, or nearly pure, is colorless or white or gray, and transparent or translucent Its luster is pearly on cleavage surfaces and satiny on fracture surfaces Its hardness is about 4 5 and its den- sity 2 88. When broken in the dark, some specimens phosphoresce Its average refractive index for yellow light is i 61.
Before the blowpipe the mineral fuses to a white enamel It yields water when heated in the closed tube and when treated with hot hydro- chloric acid it decomposes, leaving a residue of flocculent silica.
The principal alteration product of pectohte is talc (p 401).
Synthesis — Small, fine needles of pectohte have been produced by heating to 400° mixtures of Si02, AkOs, Na20, CaO and BfeO, in various proportions
Occurrence.— The mineral occurs in druses and as isolated crystals on the walls of cracks m eruptive rocks, and also in a few instances as vein fillings, and as a constituent of metamorphic rocks. It is mainly a secondary mineral
Localities —Crystals are found in seams m basalts at Edmburghshire, Scotland, at Bergen Hill, N J , in clefts in traprock, and in the eleohte- syemte at Magnet Cove, Ark (manganopectohte with about 4 per cent MnO) At Barrow Point, Alaska, fine-grained fibrous aggregates are found in abandoned workshops of the Eskimo Radially fibrous masses occur in the Thunder Bay region, Lake Superior, at Dibco, Greenland, and at a number of points in the Alps.
Magnesmm-Calcium-Iron Pyroxenes Diopside-Augite
The calcium-magnesium-iron pyroxenes include a number of com- pounds that have been given distinctive names They are apparently isomorphous mixtures of the metasihcates of Mg, Ca, Fe and Mn, or of these together with the magnesium and iron salts of the basic orthosilicate of iron and aluminium (Mg-Fe)((Al- Fe)0)2Si04.
The crystals of all members of the group are alike in habit and similar m their mterfacial angles Their axial ratios are nearly the same and the angle ft has nearly the same value in all It is possible that the slight differences observed are due to the effect of the varying amounts of iron present. The crystals are nearly all short columnar in habit, with
Anhydrous Metasilicates
the vertical zone well developed The simplest crystals are bounded by ooPob(ioo), ooP(no), ooPSb(oio) and P(Tii), but — P(III), 2P(22i), oP(ooi) and 2P 02(021) are also common (Fig 201) Other forms to the number of 95 have been observed, but they are compara- tively rare Contact and interpenctration twins are fairly common In the contact twins the usual twinning plane is oo P 66 (100) (Fig 202) Polysynthetic twins are twinned parallel to oP(ooi) In the mterpene- tration twins — POO(IOI) (Fig 203) and Fa (Is 2) are the twinning planes The cleavage is parallel to oo P(iro), the cleavage angles being about 93° and 87°* Partings are also common, parallel to one or the other of the three pinacoids
All the pyroxenes of this group have a glassy luster and are trans- parent or translucent, Their color varies with composition as does also
A
Fig 201
Fig 202.
FIG 203 FIG 201 — Axigilc Crystal with oo P, no (m), oo P 55 , joo (a), oo P So , oio (b) and
P, Tn(s),
FIG 202, — Augitc Twinned about oo P 65 (100) FIG 203 — Interpenetration Twin of Augitc, with -P So (101) the Twinning Plane
their hardness and density. The limits of hardness are 5 and 6 and of density 3 2 and 3 6. The streak of all varieties 'is white Pleochroism has been observed in some occurrences but it is not as noticeable as in the corresponding amphiboles. In the pyroxenes of this group it is usually in shades of green, but in the diallage of the Lake Superior region it is fairly strong in shades of amethyst
Before the blowpipe the members of the group are fusible, their fusibility increasing with the quantity of iron present The fusing temperature of the pure diopside is 1381° and of hedenbergite xioo°- 1 1 60°, The fusing points of the other pyroxenes of the group he between these temperatures None of the varieties are attacked by acids to any appreciable degree
All the pyroxenes are distinguished from other minerals by their crystallization and their cleavage.
Descriptive Mineralogy
Diopside is a mixture of the magnesium and calcium silicates m which the two molecules are in the ratio i i With the addition of the cor- responding iron molecule diopside grades into sahlite The calculated composition of a mixture of the formula MgCa(SiOs)2 is indicated in the first line The compositions of several typical diopsides are quoted in the following two lines
Theoretical Albrechtsberg, Aus Alathal, Switzerland
Si02 A1203 Fe203 FeO MgO CaO Total
55 55 18 52 25 93 100 oo
55 6o l6 56 18 34 26 77 101 43
54 28 51 98 i 91 17 30 25 04 100 02
Its crystals are usually characterized by the presence of the basal
plane (Fig 204) The value of the angle no A 110=92° So'
Diopside is usually light green or colorless, yellowish, dark green or nearly black and rarely deep blue The lighter varieties are transpar- ent or translucent, the darker ones opaque The density of the pure mineral is 3 25. Its refractive indices for yellow light are. 1.6685,18= 1.6755, 7=16980, All these values increase with increase in the iron molecule Among the varieties that have been given distinct names may be mentioned Malacohte, a pale colored translucent variety, and Chromeopstde, a bright green variety containing from one to several per cent CtaOs
Diopside occurs in igneous rocks and in metamorphosed limestones.
Hedenbergite is the calcium-iron pyroxene, though it always con- tains some of the diopside molecule The calculated compositions of the type mineral (FeCaS20e) and of a specimen from its best known locality
FIG 204 — Diopside Crystals with oop, uo (m), oo Poo, 100 (a), oopSb,Oio (6), oP ooi (c), -P, in +2P, 221 (o), 3P3, 31 1 (A), +P5o,Toi (p)
are.
Theoretical Tunaberg, Sweden
Si02 AkOa FegOs FeO
48 39 29 43
47 62 i 88 10 26 29
MgO CaO Total
22 l8 IOO 00
2,76 21. S3 lao 18
Anhydrous Metasilicates
The mineral is black, except varieties that contain Mn which are grayish green It occurs in crystals (Fig 205) and m lamellar masses Its density is 3 31, and refractive indices for yellow light, i 7320, /3=i 7366, 7 1 7506
m
Sahhte. — Intel mediate between diopside and hedenbergite are several pyroxenes which are characterized by possessing all three of the elements Ca, Mg and Fe in notable amounts Of these the most common is sahhte, which is FIG 205 —Hedenbergite grayish, grayish green or black It occurs m Crystal Forms a, crystals and granular masses
A typical analysis follows, the specimen
, tr , , J A
coming from Valpelema, Italy
in F'? *°4 Also aP
021 (s) and
Si02
FeO
MgO
CaO
Total
Schefiferite is a brown or black pyroxene characterized by the fact that it contains considerable manganese It may be regarded as heden- bergite m which a portion of the iron molecule has been replaced by the corresponding manganese molecule A specimen from the best known locality for the species — Langban, Sweden — gave*
28,
17, CaO=i9 62=99 22
It occurs m tabular crystals that aie usually elongated m the direction of the zone ooPob (oio), P(Tn), Poo (Tor) and in crystalline masses
The mineral is yellowish brown or black, according to the percentage of iron present Its sp gr. is 3.46-3,55 and its fusing temperature
I200°-I250°
A fine blue variety, known as wolan, from St Marcel, Italy, is char- acterized by the presence of about 5 per cent NagO, due possibly to the admixture of NaMn(SiOa)2 Its sp gr.=3 21.
Jeffersonite is a variety containing zinc, occurring at Franklin Fur- nace, N J. It is found in large crystals with rounded edges Its color is greenish black on fresh fractures and chocolate brown on exposed sur- faces. An analysis yielded
Si02 AlaOs FeO MnO ZnO MgO CaO H20 Total 49 91 i Q3 ro 53 7 oo 4 39 8 18 15 48 i 20 9862
374 Descriptive Mineralogy
Augite is the name given to the Ca-Mg-Fe pyroxenes containing alumina They are isomorphous mixtures of (Ca, Mg, Fe) SiOa with the alumino and ferric orthosilicates of the same metals, and often with a small quantity of the acmite or jadeite molecule The varieties of augite are numerous, their composition and properties differing with the pro- portions of the various molecules in the compounds The three most prominent varieties are
Fassatie, a pale to dark green richly magnesian variety Sp gr
Ordinary augite a dark green or brownish black vanety, common in igneous rocks Specific gravity 3 24 For yellow light, a=i 712, 5=1717,7=1733
Diallage, a variety that is characterized by the possession of a distinct parting and a lamellar structure, usually parallel to oo P 60 (100).
Omphacite is a bright green sodic variety Sp gr 33 Analyses of fassaite (I), of three varieties of augite (II, III, IV) and of onipha- cite (V) follow.
Si02 A1203 Fe20a FeO MgO CaO Na20 Loss Total
I 41 97 10 63 7 36 55 26 60 10 29 2 70 100 10
II 50 41 6 07 i 09 6 78 12 92 22 75 100 02
Iii 51 01 4 84 3 51 3 16 16 58 20 80 99 90
IV 46 95 9 75 4 47 4 °9 °4 19 02 . 100 32 V 54 21 10 91 3 12 i 33 10 03 14 61 4.51 .05 100 15
I Grass green, Fassathal, Tyrol II Yellow, Monte Somma, Italy
III Dark green, Monte Somma, Italy
IV Black, Monte Somma, Italy
V Omphacite from the Eclogite of Otztal, Tyrol Also 92% KaO and .46% TiO8.
The augites are usually in short prismatic crystals (Figs. 201, 202). They are common constituents of igneous rocks
All the pyroxenes of this group are subject to change under the conditions on the earth's surface Under the influence of the weather they alter to chlorite Under metamorphosing conditions they change into the corresponding amphiboles, more particularly into the bright green variety known as urahte. Alteration to serpentine is also common. Steatite, tremohte, epidote and other minerals are also frequent alteration products
Anhydrous Metasilicates 375
Syntheses — Diopside and augite are common m furnace slags. They have been made by fusing their constituents m open crucibles, with or without the addition of a flux Molten hornblende crystallizes as monoclmic pyroxene
Occurrence — The most common methods of occurrence of the various pyroxenes have already been mentioned The magnesium-calcium varieties such as diopside and sahlite are found principally in metamor- phic limestones The green varieties are most common in schists and the black varieties m igneous rocks, especially the basic ones Augite often occurs also in ore veins, especially with magnetite
Localities — The occurrences of the various pyroxenes are so numerous that they cannot be enumerated here It will be sufficient to state that good crystals of diopside are found m the Ala Valley, Piedmont, at Zer- matt, in Switzerland, at Pargas, in Finland, and Nordmark, m Sweden. Hedenbergite occurs at Tunaberg, Sweden, and Arendal, Norway, scheffente at Langban, Sweden, and augite at Mt Monzom, m the Fassathal, Traversella, Piedmont; Mt Vesuvius, Italy, the Sandwich Islands and the Azores
In the United States good crystals are found at Raymond and Rum- ford, Me (diopside, sahhte), at Edenville and Dekalb, N Y (diopside), and at Franklin Furnace, N J (hedenbergite and jeffersomte)
Alkali Pyroxenes
The alkali pyroxenes are characterized by the piesence m them of alkalis, especially sodium They may be regarded as isomorphous mix- tures of the sodium, lithium, iron and aluminium metasihcates, thus Na2Si03+Fe2(Si03)3~2NaFe(SiO;j)2, or NasSiQs+AhKSiOsJs-aNaAl ($103)2 The three most common alkali pyroxenes are acmite, jaderie and spodumene Spodumene is used as a source of lithium Jadeite was formerly a favorite material from which to carve sacred emblems
Acmite— Aegirine
Acmite has a composition corresponding to the formula NaFe(SiOa)2, and is rare More commonly this molecule is mixed with the augite molecule in the compound known as aegmne or aegmte, or aegmne- augite) according to the proportion of the augite molecule present When the mixture contains about 2,50 per cent Na20 the correspond- ing mineral is usually known as aegerine-augite. When MgO and CaO are absent (NagO5* 12-13 per cent), it is known as acmite. Between these limits it is aegirine.
The calculated compositions of the pure acmite molecule and the
Descriptive Mineralogy
composition of specimens of acmite, aegirme and aegirme-augite as found by analyses are
Sl02
I Si 97
Ii. 51 66
Iii 49 3 2
A1203 Fe203
4 88 16 28
Iv. 5° 33 30
FeO MgO CaO
5 65 4 28 9 39
12 37 10 98 22 01
Na20
K20
Total
100 Oo
too 25*
ioo 41 t
99 73 J
I Theoretical acmite II Acmite, Rundemyr, Norway
III Aegirme, Sarna, Dalekarhen
IV Aegirme-augite, Laurvik, Norway
Contains also 69 per cent MnO, 39 per cent H20 and i 11 per cent TiOj t Contains also i 25 per cent TiOa t Contains also 66 per cent TiQj
Acmite crystals are usually more acicular m habit than those of the ordinary pyroxenes, and their terminations are steeper P(Tn) and Poo(Toi) are common and 6P("66i) and other steep pyramids are not uncommon (Fig 206).
The mineral has a vitreous luster, and is transparent or translucent Its color is reddish brown to brownish black and In some cases green Its hardness is 6 and sp gr. 3 52 Its refractive indices for yellow light arc. a 1,7630, j3=i 7990, 7=1 8126
Aegirme is greenish black Its streak is yellowish gray or dark green. Plcochroism is strong in green and brown tints. Haulncss is 6 and density 3 52
Before the blowpipe acmite and aegirine fuse to a black magnetic globule The fusing tem- perature of acmite is from 970° to 1020° Both minerals are slightly attacked by ucul before and after fusing
Synthesis —Acmite has been made by the
fusion of a mixture of powdered quartz, FfyQz and NiioCO;* in the pro- portions indicated by the formula NaFe(SiOs)2
Occurrence — Both minerals are limited m their occurrence to soda- nch igneous rocks, in which they are primary
Localities — Crystals of acmite occur in a dike of pegmatite near Eker, Norway, and in a nephelme syenite at Ditro, Hungary.
FIG 206 — Acmite Crys- tal with oo p 60 , ioo (a), oo Poo, oio (6), _oop, no (m), +P, in (5), +3P5> 3" (5), +6P, 56t (0) and 8P, SSi (12) 0 and Q merge
Anhydrous Metasilicates 377
Aeginne crystals are more common They occur abundantly in the nephehne syenite dikes in the neighborhood of Langesundf jord, Norway, m some instances in crystals a foot long. They are found also in can- cnmte syenites at Elfdalen and elsewhere in Sweden, in nephehne syenite on the Kola Peninsula, Russia, and in the same rock at Hot Springs, Ark.
Jadeite (NaAl(Si03)2)
Jadeite is not known in measurable crystals, but, because sodium is almost universally present in the mineral spodumene, where it is ap- parently in isomorphous mixture with LiAl(Si03)2, it is assumed that the molecule NciAl(Si03)2 ciystalhzes in the same way as the spodumene and the acnnte molecules Most specimens of jadeite are isomorphous mix- tures of the jadeite and diopside molecules When in addition to these there is a notable admixture of the acmite molecule, NaFe(SiO,3)27 the mineral is known as chloromdamte
The mineral is of great ethnological interest because so many orna- ments were made of a rock composed mainly of jadeite by the ancient inhabitants of China, Mexico, South Amenca and elsewhere " Jade " ornaments, however, arc not all made of jadeite, but m all instances their material resembles this mineral in color, structure and density Many of them aie made of fibrous aniphiboles, some of which correspond to jadeite in composition
The theoietical composition of the mineral is given in line I, and the analyses of specimens from Mexico and China in lines II and III,
AbO,i FcO MgO CaO NagO KgO H20 Total
I 59 39 25 56 IS 35 ioo oo
II 58 18 23 S3 i 67 1,72 2 35 n 81 77 53 100 56
Iii. 58 68 21 56 94 2 49 3 37 13 09 49 . . 100 62
I Theoretical II Oavua, Mexico III Ornament, China
Jadeite occurs in fibrous, flaky and dense, finely granular masses with a glassy luster, inclining to pearly on cleavage surfaces Its color is in some cases white or yellowish white, but more frequently bright green or bluish green. Its streak is white Its cleavages make angles of 87° Its fracture is tough and splintery. Its hardness is 6 7 and its density 3.3-3 35. Its intermediate index of refraction, 1.654
Before the blowpipe jadeite fuses easily lo a transparent, blebby glass It is unattacked by acids. After fusion, however, it is easily decomposed
378 Descriptive Mineralogy
by HC1 and sometimes by Na2C03 At high temperatures (225° 235°) it is also decomposed by water
Jadeite alters by metamorphic processes to a white hornblende (tremohte)
Localities —Ornaments and instruments made of jadeite, and water- worn fragments of the mineral are known from many localities in China, Tibet, Burma, Switzerland, France, Egypt, Italy, Mexico and Central America The original sources of the material of the ornaments are not known The mineral, however, occurs with albite and nephelme in a dike at Tawman, Burma, and probably as a constituent in some metamorphic schists.
Spodumene (LiAl(Si03)2)
Spodumene is essentially the lithium molecule corresponding to the sodium molecule jadeite Nearly always, however, the mineral contains some of the sodium molecule, and a small quantity of helium Three typical analyses are quoted below
Colorless, Yellowish green, Kun*lto,
Theoretical Branchville, Mmas Geraes, S Diego
Conn Brazil Co , C tl
Si02 64 49 64 25 64 32 64 42
27 44 27 20 27 79 27 32
FeO 67
CaO 17
Li20 8 07 7 62 74? 7 20
Na20 39 55 39
K20 . 03
Total 100 oo 99 90 101 07 99 51
Crystals are usually columnar parallel to oo P (no) or tubular par- allel to oo P 66 (100) (Fig 207) They are more complex than those of the members of the diopside-augite group and their habit is different The most frequent forms are ooP 60(100), ooPob(oio), coP(ixo), ooP2(i2o), ooP3(i3o), 2PSb(o2i), 2P(22i) and P(Tn) Some of them are of enormous size In the Etta Mine, Black Hills, South Dakota, are many 30 ft long and 3-4 ft. in diameter. One meas- ured 47 ft, in length. Most crystals are striated vertically. Twins are
Anhydrous Metasilicates 379
fairly common, with ooP(no), the twinning plane Although crystals are not uncommon the mineral more fiequently occurs as platy or scaly aggregates The angle no A ilo=93°
Spodumene has a glassy lustei, which is pearly on cleavage surfaces Its color is white, gray, greenish or yellowish green, or amethystine It is transparent or translucent, and its streak is white Its fracture is uneven or conchoidal, its hardness between 6 and 7 and its density 3 2 Dark green crystals exhibit marked pleochroism Refractive indices for yellow light in speci- mens from North Carolina are a=i65i, 18=1669, 7=1677
Two varieties have been named and used as gems These are FlG 2°7 —Spodumene Crys-
OAMfe, a glassy emerald-green variety, gj from Alexander Co , N C I20'(ju), £
Kutste, a pmk or lilac variety, from 130 2? So, 021 (d), San Diego Co , California Under the mflu- -HP, 221 (r), +P, m ence of radium rays it becomes green When M 2P2, 2 1 1 (/) and P 65 ,
Ioj
heated to 240° it becomes a darker rose color, but at 400° it loses all color
Before the blowpipe the mineral swells up and fuses to a colorless glass, at the same time imparting a crimson color to the flame It is unat tacked by acids. It melts at about 1325° Its powder reacts alkaline
It alters readily to albite, muscovite, eucrypfate (LiAlSiOt), or mix- tures of these One of the commonest mixtures is known as cymatchte or cumatohte. The mixture of albite and eucryptite has been called $ spodumenc,
Spodumene crystals have not been made artificially
Occurrence atid Origin — The mineral occurs in granites, pegmatites and ciyRtallme schists, where it was formed by pneumatolytic processes It is often associated with cassitente
Localities — Spodumene crystals occur at Huntmgton, Mass , in a quartz vein m mica schist, at Branchville, Conn ? in pegmatite, at Stony Point in Alexander Co , N. C , in cavities m a gneiss, at the Etta Mine and at other places in the Black Hills, N D,, in a pegmatite; at the lepidolite localities in California and in Mmas Geraes, m Brazil
Uses —The ordinary varieties of the mineral are used as a source of lithium m the manufacture of lithium salts, and the transparent varieties
Descriptive Mineralogy
as gems The total production of kunzilc m this country during 1912 was valued at $18,000, all from California One specimen found in this year weighed 47! oz Another was a crystal measunner 9X5X7 inches The other forms of the mineial were not mined In teccnt years a few tons have been furnished by the mines in the Black Hills
Tricl1Nic Pyroxenes
The trichmc pyroxenes include the four mmcials rhodonite, bmtamtlc, fowlente and babingtonite They are completely ibomoiphous The first is the manganese metasihcate, MnSiOs, and the otheis aic iso- morphous mixtures of this molecule with the con expending silicate of calcium (bustarmte), or of these two with the corresponding 11011 (babmg- tornte), or with the iron and zinc compounds (fowlente)
Rhodomte—Fowlente (R"MnSiOa. R Ca,Fe,Zn)
Rhodonite is the pure manganese silicate with the pcitentagc com- position shown in I In II is the result of an analysis of ciyslals fiom Pajsberg, Sweden An analysis of bustamite fiom Campiglia, Italy, is quoted in III and one of fowlente from Franklin Funute, N J., in IV
Si02 A1203 MnO FeO ZnO M0 CaO HaO Total
I 458s
Ii 45 86
Iii 49 23
Iv 46 06
54 Is
34 28 3 63 7 33
Joo Oo
All are trichmc (pmacoidal class), with the aual constants of
10729 : T : .6213, =-io3°
lO'.jS-ToB'.r-Si0 JO'
for rhodonite, and i 0807 : i : .6237 and 01-102° 27', jS=io8°34/, 7-82° S3X for bahmgtonitc. Thoir crys- tals possess many habits, of which the cubical, tabular, and columnar arc the most Fig 208 —Rhodonite Crystals with 'p, i7o common. They ank usually
(JO* °°P'' 110 oP, ooi oo pas, rough with rounded edges,
ioo (a) I,-" Poo ,010(6), 2,P, 221 Wand
221 (n)
oo P 08(100), oo P 06(010),
The most frequontiy
curnng forms are oP(ooi), oo'PCiTo), P/(iu") and
2,P(22i) (Fig 208) The angle ioo A 001*72° 37', Their cleavage
Anhydrous Metasilicates 381
is perfect parallel to ooP'(no) and oo 'P(i To) Although crystals are fairly common in some places, the minerals are more usually in dense, structureless or finely granular masses
All the trichnic pyroxenes have a glassy luster which is somewhat pearly on cleavage surfaces They are transparent or translucent and all except babmgtomte have a rose-red color when pure When mixed with other substances their color may be yellowish, greenish, brownish or black They are pleochroic in rose and yellowish tints Their streak is always reddish white Babmgtomte is greenish black and is pleo- chroic in green and brown tints All have an uneven fracture Dense varieties are tough and their crystals are brittle Their hardness 5-6, and density 3 4-3 7 The intermediate refractive index of rhodo- nite is i 73 for yellow light
Before the blowpipe all become black, swell and fuse to a brown glass The fusing tempeiature of rhodonite is about 1200° and of bustarmte about 1300° They are attacked by acids with loss of color
When exposed to the weather the membeis of the group containing manganese alter to a mixture of which the principal constituents are a manganese OKide, MOs, silica and water, or to mixtures of carbon- ates of manganese, or a mixture of the carbonates of manganese, iron and calcium
Syntheses — Crystals of rhodonite have been prepared by fusing a mixtuie of SiCfe and MnCte and bypassing a current of steam and COa over a icd-hot mixture of MnCb and Si02 Rhodonite and babmgton- ite crystals are also formed in the slags of manganese iron furnaces, and the latter has been found in cavities in roasted iron ores
Occurrence — The members of the group containing manganese occur m veins of magnetite, copper and other metals, and in contact zones between limestones, shales and igneous rocks, associated with other manganese minerals. Under these conditions they may have been pro- duced by the help of magmatic emanations Rhodonite occurs also with rhodochrositc in deposits of manganese ores and in other associations, where it may be of secondary origin. Babmgtomte occurs principally as a rare component of siliceous rocks
Localities — Crystals of rhodonite and bustamitc occur in iron ore deposits in the gneiss of Langban, Sweden Fine crystals of rhodonite are found m the iron ore at Pajsbcrg, Sweden, and crystals of fowlente in metamorphosed limestone associated with the zinc ores at Stirling Hill and Franklin Furnace, N J Massive rhodonite is abundant at Jekatermburg, Ural, Russia, at Kapmk, Hungary, at Blue Hill Bay, Maine, and in Jackson Co., N C, associated with wad Massive bus-
382 Descriptive Mineralogy
tamite occurs at Rezbanya, Hungary, in veins m limestone, and at Mts Civillma and Campigha, Italy, m fibrous masses Babingtomtc occurs in a mica schist at Athol, Mass , and m druses in granite at Baveno, Italy, and in the ore veins at Arendal, Norway
The principal occurrences of gem rhodonite in this country are in Siskiyou Co , Cal , and near Butte, Mont In the former locality the mineral occurs nine miles north of Happy Camp m a fine-grained quartz schist It consists of a mixture of quartz grams cemented by rhodonite and traversed by veins of pyrolusite The Montana material is in radiating groups with quartz, pyrite and brown manganese ovide At the Alice Mine it is associated with rhodochrosite
Uses and Production — Transparent rhodonite is used as a gem-stone to a slight extent The total yield of the material m the United States during 1912 was valued at $550,
THE AMPHIBOLES (R"Si03, R'At(Si03)2 and R"(R"'0),Si04)
The amphiboles are common alteration products of pyroxenes and some other silicates The> are also abundant as components of ceitain schistose rocks, as for instance, the hornblende schists, and they otuu also as original constituents of igneous rocks. The crystals of till the amphiboles are similar m habit to those of the pyroxenes (Fig 209), but since the ratio between the a and b axes is about to i , the angles between their cleavage planes, which, like those of the pyroxenes, are parallel to ooP(no), are from 54° to 156° and 124° to 126° (see Fig igSB) The plane of symmetry bisects the obtuse angle.
The members of the group are about as numerous (is those of the pyroxenes, but the common types are much fewer. Moreover, there is no subgroup corresponding to the wollastomte subgroup of the pyrox- enes. The best known members of the series, with their axial Mtios *ire:
Orthorhombit (possibly twinned monoclhuc)
Anthophylhte f (Mg Fe)SA 1 fl fc - 521 : i a-fe
Gcdnte (Mg.Fe)(A10)2&iO4 -.523 i . .17
Monochmc (monochmt prismatic class),
Tremolite MgsCa(Si08)4 a 6 : r,s4T5 ' r .3886
Actouhte (Mg Fe)8Ca(Si03)4
Cummingtonite (Fe MgJSiOj Gr&nente FeSi08
" (Mg Fe),Ca(Si08)<
Hornblende
(Mg Fe)((Al NaAl(Si08)3
Anhydrous Metasilicates 383
}NaAl(Si03)2 1 Glaucophane (Fe Mg)SlOl S3 i 29 /3-77°
[ (Na2 Ca Fe)Si03 ]
Arfvedsowte (Ca Mg)((Al Fe)0)2SiO' J " S496 r 2°75 0 75°45'
Riebeckilc NaFe(SiO,)2 =5475 i 2925 0 76°lo'
Crocidohte j jo ]
Tnclmic (tnclmic pinacoidal class) Aemgmatite Na4Fei)(Al Fe)(Si TiJiO* 6778 i 3506 j8 72°49'
Orthorhombic Amphiboles
Anthophyllite— Gedrite
The orthorhombic amphiboles are comparatively rare They are isomorphous mixtures of MgSiOa, FeSiOs and the alummo-orthosihcates (Mg- Fe)(A]0)oSi04 The pure MgSiOa has not been found in nature, but it has been produced in the laboratory The mixture of the mag- nesium and iron silicates (Mg-Fe)Si03, is known as anthopkylhte. In nature it always contains a little of the molecule (Mg-Fe)(A10)sSiOi Gedrite, which is much less common than anthophyllite, contains more AbOs than does this mineial, which may be regarded as due to a larger admivtuic of the molecule (Mg Fe)(A10)2SiOi. The name is thus applied to aluminous anthophylhtcs
The difference in composition of the two minerals is shown by the following analybct. of (I) anthophylhte and (II) gednte
Si02 FeiAi AbO,j MnO FeO MgO CaO Na20 H20 Total
I 57 98 63 31 10 39 28 69 20 i 79 99 99
II 46 18 44 21 78 .. 2 77 25 05 . 2 30 i 37 99 89
I Brown crystals, Franklin, Macon Co , N C- II Colorless prisms, Fibkcrnas, Greenland
The orthorhombic amphiboles usually occur in platy or fibrous aggregates that rarely show traces of end faces, and, consequently the ratio between c and b is not accurately known. The planes in the pris- matic zone are, however, sometimes so well developed that they can be recognized as oopco(ioo), ooP 06(010), and ooP(no) Cleavage is perfect parallel to oo P(xio) and distinct parallel to oo P 36 (oio) The cleavages intersect at angles 54° 2o'-55° i8\
The minerals have a glassy luster which is slightly pearly on cleavage surfaces They are green or brown in color and have a colorless, yellow white or gray streak and are translucent and pleochroic in colorless,
Descriptive Mineralogy
greenish and brownish tints Their fracture is somewhat conchoidal Hardness is 5 5 and density 3 2 The refractive indices for yellow light m anthophyllite are =1633, 18=1642, 7=1 and in gednte, i 623, i 636, and i 644
Synthesis — Pure magnesium metasihcate has been made in ortho- rhombic crystals mixed with monochmc crystals, by rapid cooling of a magma made by heating Mg salts and silica with water at 375°-47s°
Occurrence — The minerals are found in crystalline schists — more particularly in hornblende gneisses and hornblende schists, where they are distinctly metamorphic minerals, having been derived in some cases, at least, by the alteration of the orthorhombic pyroxenes They alter to talc
Localities —Anthophyllite occurs in dark brown platy abrogates at Kongsberg and Modum in Norway, associated with hornblende in mica schists, on the Shetland Islands, Scotland, associated with sei pen tine, and at the Jenks Corundum Mine in Macon Co , N C
Gednte occurs in yellowish gray fibrous aggregates at Bamlc, Norway, in dark brown aggregates associated with magnetite and brown mica, at Gedres, Hautes-Pyr&iees, France, and m a mica schist at Fiskernas, Greenland, associated with a large number of metamorphic minerals
Monoclinic A.A1Phibol&S
The monochmc amphiboles, like the corresponding pyroxenes, com- prise isomorphous mixtures of the metasihcatcs of No,, Mg, Ca and Fe
m
a
m
j/
/
FIG 209 — Ampibole Crystals with °o P, no (m}, oo p Sb , oio (6), PJ, 130 (e); P w , on (r) and -P So , jor (/).
and the basic orthosihcates of Al and Fe Recent work seems to indi- cate that in tremolite there is present also a little HkCX In the amphi- boles the alummo-silicate is more common than in the pyroxenes and consequently aluminous amphiboles are more common than aluminous pyroxenes
Anhydrous Metasilicates 385
All the monoclimc amphiboles crystallize with the same habit in crystals that are columnar like those of the corresponding pyroxenes, but on which the terminations are different (Fig 209) Moreover, all have a distinct cleavage parallel to oop(no) with cleavage angles of about 56°-! 24°
The amphiboles aie distinguished from other minerals by their crystallization and their cleavage
For convenience, the monoclimc amphiboles may be subdivided into (i) the magnesium-calcium-iron amphiboles including tremolite actino- hte, cummmglomte, gtunente and hornblende, and (2) the alkali amphi- boles, including aifvedsomte, glaucophane and nebecfote
Before the blowpipe all the members of the group fuse to a glass which is coloiless, green or black, according to the quantity of iron present The varieties rich in iron are attacked by acids
Magncsium-Calcium-Iron Amphiboles Tremohte-Hornblende
This group includes the monoclimc amphiboles that are mainly meta- silicates of magnesium and iron and the mineral hornblende, which is a mix- ture of these molecules and the orthosihcate (Mg Fe)((Al'Fe)0)2Si04 The calcium mctasihcate is present in some members as an isomorphous mixture, but it does not occur alone as an independent member corre- sponding to wollastomtc among the pyroxenes Hornblende is the only member of the series that is essentially aluminous
The crystals of the monoclimc amphiboles are short columnar or long and acicular. Their axial ratios are nearly alike and their cleavage angles differ only by a few minutes. The simplei crystals are bounded by ooPob(ioo), oo P 03(010), ooP(no), oP(ooi), 3? 00(031), +P6o(Toi), -Pob(iot), 2P2(T2i), 2PI(2ii) and POO(OII) (Fig 209). Contact twins arc common, with cop<x>(ioo) the twinning plane as m the pyroxenes Polysynthetic twins are larc
All the amphiboles of this group have a glassy luster and are trans- parent or translucent All the members but hornblende arc white or some shade of green, though colorless and brown varieties are not un- common and yellow and red varieties are known. Hornblende is fre- quently so dark as to be almost black Their streak is light, hardness is 5-6 and density 2 0-3 depending upon composition
The cleavage is perfect in all the amphiboles and there is present often also a parting parallel to oo P oo (too) and P oo (Toi), the latter due to gliding Pleochroism is strong m all the colored varieties m green
386 Descriptive Mineralogy
and yellowish green tones in the green varieties, and brown and yellow- ish brown tints in the brown varieties
Tremolite is the calcium magnesium silicate When there is mixed with this the corresponding iron molecule the mixture is known as actinohte if the proportion of the iron molecules present is not great The theoretical compositions of the two molecules Mg3Ca(Si03)4 and Fe3Ca(Si03)4 are given in lines I and II, and analyses of several trem- olites and actmolites in lines III, IV, V and VI The almost universal presence of small quantities of water m trcmohtc, and the Lick of enough Mg, Ca, Fe and other metallic bases to satisfy all the SiOj re- vealed by the analyses has suggested to some muicialogLsts that the water is an essential part of the compound, and that its composition is best represented by
Si02 A1203 Fe203 FeO MgO QiO Na2O HoQ Total
I 57 72 28 83 13 41) ioo oo
II 46 90 42 17 10 93 ioo oo
III 58 27 33 tr 25 93 ii 90 T 25 i 22 09 40*
IV 57 40 38 i 36 2S 69 89 40 99 12 V 58 80 3 05 22 23 16 47 TOO 55
Vi 55 50 6 25 22 56 13 46 A 29 99 06
I Theoretical for MgsCa (SiO.)*
II Theoretical for Fc,Ca (SiOi)4
III Tremohte, Easton, Pa
IV Tremolite, Gouverneur, N Y V Asbestus, Bolton, Mass
VI Actmohte, Gremer, ZillerLhal, Tyrol
*Also oSMnOand 42
Tremolite is white 01 nearly white, and actinolite is green The former occurs in columnar crystals, in plates and occasionally in libers, while actinolite is nearly always in long, slender acicular crystals without terminations The refractive indices for yellow light in tiemoliteiue ct-i 6065, j8=i 6233, 7=1,6340. In actmohie, j~i,6n(), 0=-i 6270, 7=16387
Both minerals melt in the blowpipe flame, the fusing temperature for tremohte being about 1290° and for actinolite about 1150°.
Asbestus is a fibrous variety of tremolite, actinolite or anthophylhto. It occurs principally in rocks that have been crushed and wheaml under great pressure The actinolite asbestus is used for the same purpose as the chrysotile variety (see p 398), but it is regarded as less valuable.
Anhydrous Metasilicates 387
Its principal source in this country is Sails Mountain, Georgia, but prom- ising deposits have recently been reported near Kamiah, Idaho At the Georgian locality the asbestus forms distinct lenses in gneiss It is possibly an altered basic intrusive rock,
Smaragdite is a grass-gieen actmohte, which is often an alteration product of pyroxenes and ohvine The name is also applied to a bright green hornblende containing a little chromium
Nephrite is a finely fibrous actmohte or tremohte and usually some chlorite, forming dense rock masses that are white or of a light green coloi It was formerly much ubed, like , in the manufacture of images, charms and implements
Cummingtonite a,nd grimerite aic amphiboles containing notable quantities of the molecule FcSiO* In grunente, the qudntity of Mg present is very small but in cummmgtomte it is fairly large Because of its similarity to anthophyllite, this mineral is frequently referred to as amphibole-anthophylhtc It is intermediate in composition between grunente and actmohte Analyses of specimens from several well known localities are quoted below
SiOa Al2Ch FcaOs FeO MgO C<iO Na20 H20 Total I 57 26 75 i 73 15 64 21 70 tr 2 80 99 88
II 47 17 i oo i 12 43 40 2 61 i 90 47 2 22 100 08
I Cummingtonite, near Baltimore, Mel
II Grunente, CollobriSres, France Contains also, 07, KaO 07 and
These two minerals are comparatively rare and have not always been recognized as worthy of different names In general appearance they are much like actinohte, though perhaps more brown or gray in color, and they occur in nearly the same association The specific grav- ity of cummmgtonite varies between 3 i and 3 3 and that of grunente is about 3 52. The intermediate refractive index for yellow light is i 62- 1.65 in cummmgtonite and 1.697 in gninerite
Hornblende is the name given to the monoclmic aluminous aznphi- boles that contain only a small quantity of alkalies. In other words, most of the hornblendes are isomorphous mixtures of the actinolite mole- cule and the molecules (Mg- Fe)((Al- Fe)0)aSi04 and (Na- K)Al(SiO)2 The varieties containing NdaO (known as katojorrfc) correspond to aegirme among the pyroxenes
388 Descriptive Mineralogy
The varieties of hornblende that are distinguished by distinctive names are
Pargasite, the green, bluish green or greenish black variety, and
Edemte, the white, gray or light giccn variety, both of which con- tain very little iron m either the ferrous or feme condition,
Smaragdite, a bright green chromiferous variety of parasite,
Common hornbletide, the greenish black vanety,
Basaltic hornblende, which contains a laige pioporlion of ferric iron and is black in color
Their refractive indiceb for yellow light aic as follows
Pargasite, Pargas, Finland i 613 i 020 r 632
Common Hornblende, Kragero, Norway t 629 T 042 i 6153
Basaltic hornblende, Bohemia i 680 i 725 t 752
The fusing temperature of pargasitc is about 1150° and of horn- blende about 1200°
Analyses of typical specimens of these varieties follow
Si02 A1203 Fe203 FeO MgO CaO Niii0 KaO Tn Total
I 51 69 4 17 2 34 9 83 17 17 12 17 82 79 i 100 25
II 42 97 16 42 . i 32 20 14 14 90 i 53 2 85 87 102 75
IV. 39 17 14 37 12 42 5 86 10 52 n 18 2 48 2 OJL 39 99 91
I Common Hornblende, Vosges Aho 14 per cnl
II Pargasite, Pargas Finland Also i 66 per tent F
III Edemte, Saualpen, Cannthia Also 1.21 per tent K
IV Basaltic, Jan Maycn, Greenland Albo i 51 [>er <uul MtiO
Among the commonest forms of alteration in lhi umphihoIoR are the following Tremolite into tile (p 401) and wipcntiiu*, and hornblende into serpentine, chlorite (p 428),q>idolu and Imitiie, often with the addition of magnetite and other iron compounds in oases where iron was present in the original mineral Most of these thungcs me brought about by regional metamorphism. The production of hiotiie is also brought about by the action of magmas The common weathering products of hornblende are chlonte, epidote, culcite, quarts, magnetite and sidente Under the conditions of high temperature and high pres- sure, hornblende sometimes passes over into augite and magnetite.
Syntheses.— Amphibole crystals have not been found in slags nor have they been made by dry fusion. Crystals of hornblende, however,
Anhydrous Metasilicates 389
have been obtained by heating to 555° for three months, a mixture of its components in a glass tube with water
Occurrence — Tremolite occurs m crystalline limestones and dolo- mites that have been subjected to regional metamorphism and in crys- talline schists Actmohte, cummmgtomte and grunente are found in crystalline schists, in some cases m such laige quantity as to constitute essential parts of the rocks Actmohte schists are such rocks containing in addition to the actmolitc some quartz, epidote and chlorite Gru- nente schists consist essentially of gmnente, actmohte, magnetite and quarts
Common hornblende occuis m igneous and metamorphic rocks, such as gneisses and schists In some schists, as the amphibohtes, it is the puncipal constituent and m others, the hornblende schists, it is the principal component other than quartz The mineral is also a common metamoiphic alteration product of pyroxenes which it frequently pscudomorphs When the pscudomoqjhmg hornblende ib blue-green and fibrous it is known as urahte The chemical changes attending this alteration aic illustrated by the analyses of a pyio\ene (I) from the Grua Tunnel in Norway and of the urahte (II) produced from it
AlaOs FcO MnO CaO MgO NagO Loss Total I 5° S3 27 7 81 i 99 24 51 10 92 48 26 100 37* II 42 02 2 30 3 25 9 30 94 20 90 9 63 45 i 07 100 04*
Also 19 per cent Kj0 m I anJ 26 per cent in IE
Basaltic hornblende is found only in igneous rocks, and especially those rich miion
Edenite occurs in ciystalhnc limestones that have been metamor- phosed by contact action
Pargasite is in gneisses and crystalline limestones
Localities — Tremolite crystals occui at Campolonga, Switzerland; at Rezbanya, Hungary, at New Canaan, Conn , and at Diana, Lewis Co , N. Y It occurs also in flat plates at Lee, Mass ; near Byram, N J ; at Easton, Penn , at Edenville, N Y., and at Litchfield, Me,, and other places in the limestones in Quebec, Canada
Actmohte occurs with chlorite at the Zillerthal, Tyrol, in talc and chlorite schists near Jekatermburg, Ural, Russia; at Arendal, Norway, at Willis Mt , Buckingham Co., Va , at the Bare Hills, Md,; at Mineral Hill, in Delaware Co , and at Unionville, Penn , in the soapstone quarries at Wmdham and New Fane, Vt , at Bolton, Brome Co , Quebec, and at many other points.
390 Descriptive Mineralogy
Asbestus is abundant at Sterzig, in Tyrol, on the Island of Corsic near Greenwood Furnace, N Y , in the Bare Hills, neai Baltimore, JVL at Pylesville, Harford Co , in the same State, at Barnet's Mills, Fau quier Co , Va , and at the localities at which it has been mentioned as being mined
The principal occurrences of cummmgtomte arc kongsbcig, Norway, Cummmgton, Mass, and a layer m gneisses and schists at Mt Washington, Md
Grunente occurs in a rock composed of this mineral, gai net and hem- atite near Collobneres, Var , France It has also been dcbcribcxl as the principal constituent of certain schists in the Lake Supenoi iron icgion, but since the amphibole in these locks contains a notable quantity of MgO it should better be classed -with cumminglomle
The localities at which crystals of the hornblendes have been found are very numerous. Excellent crystals occui in Ihc volcanic bombs in the Lake Laach district, Prussia, in cavities in inclusions within the lavas of Aranyer Mt , Siebenburgen, Hungary, m the dikes of porphyry, near Roda, Tyrol, on the walls of cavities m inclusions in the lavas at Vesuvius, Italy, and at various points in Sweden, etc In North America fine crystals are found at Thonu&ton, Me , at Russell and Pierrepont, N Y , at Franconia, N H , and in the glacial debris at Jan Mayen, Greenland. Pargasite occurs at Paigas, Finland, and Phippsburg, Me
Alkali Amphiboles
The alkaline amphiboles include mbeckite> croadohtc, glaucoplmue and arfvedsomte The first two are nonalummous iron-soda umphiboles and the last two are aluminous compounds Glaucophonc contains the molecule NaAl(Si03)s which is found also in hornblende, and, therefore, it may be regarded as a connecting link between the common and the alkaline amphiboles Glaucophane differs from hornblende, however, m containing very little CaO, The intermediate link halo/onto bridge* the gap between the two.
Glaucophane is, theoretically, a mixture of the two molecules NaAl(Si03)2 and (Fe- Mg)Si(X$. It is essentially u mixture of the cum- mmgtomte molecule with one corresponding to the jadeite xnolecul'
Anhydrous Metasilicates 391
among the pyroxenes An analysis of a specimen of katofonte (com- pare p 387) from the samdmite bombs in the lava at Sao Miguel, Azores, is quoted in line I for comparison with the two glaucophane analyses in lines II and III
Si02 AbOs FeaOa FcO MgO CaO Na20 K20 Total
I- 45 S3 4 10 9 35 23 72 2 46 4 89 6 07 88 99 96
IL 56 65 12 31 3 01 4 58 12 29 2 20 7 93 i 05 100 02
Iii. 56 71 15 14 9 ?8 4 31 4 33 4 80 4 83 25 100 15
I Kalofonlc, Sao Miguel, A/,orcb Also 2 96 per (cut TiOa II Glaucophane, lie dc Groi\ III Glaucoplunc, Shikoku, Japan.
Glaucophane is rarely found in crystals with end faces Even when these exist they are lough and yield poor measurements
The mineral occurs in columnar crystals, in needles and in foliated or granular aggregates in rocks Their prismatic planes are oo p 66 (100), oo P ob (oio) and oo P(iio) P(7n) and oP(ooi) are the only termina- tions that have been identified The cleavage angle is about 55° 20'.
Glaucophane is blue or bluish black, translucent and strongly pleo- chroic in yellowish, violet and blue tints. Its streak is grayish blue, its fracture uneven, its hardness about 6 and its density 3 Its refractive indices for yellow light arc i 6212, j8 1.6381, 1.6300
Before the blowpipe the mineral turns brown and then mdU to an olive-green glass It is difficultly attacked by acids.
Glaucophane is distinguished from the other amphiboloids by its color, and from other blue silicates by its crystallization, hardness and manner of occurrence,
It is usually unaltered but it has been described m one instance as being partially changed to chlorite
Synihews —It has not been produced artificially.
Occurrence —The mineral is found only in metamorphosed limestones, in mica schists and in the garnet rock known as eclogite. It is charac- teristically a metamorphic mineral
Localities.'— Glaucophane occurs m long crystals in various schists in Syra, Cyclades, Greece; in hornblende schists in the He de Groix, Brit- tany, France, in a glaucophane schist on the Island of Shikoku, Japan, and abundantly in various schists m the Coast Ranges of California,
392 Descriptive Mineralogy
Arfvedsonite, Riebeckite and Crocidohte
These amphiboles are comparatively rare They occiu principally in coarse-grained alkalme igneous rocks, usually as prismatic grams without terminations, embedded in the lock mass Arfvcclsomtc, how- ever, m some cases, occuis in groups of crystals on some of which tei- minations can be identified
Riebeckite, NaFe(S Oa)2, has a composition veiy near that of acmite, and crocidohte contains, in addition, the molecule FcSiOa Ai fvodsomte is much more complex than either of these and has no equivalent among the pyroxenes Analyses of typical specimens of the two minerals aie quoted below In line IV is an analysis of crocidohte
Si02 A1203
Fe203
FeO MgO
CaO
kjO
NaoO
IIoO
Total
49 6S
S1 °3
I Black arfvedsonitc, Kangcrdluarsuk, Greenland
II Riebeckite from granite, Qumcy,
III Riebeckite from Socotra, Indian Ocean
IV Bark blue radial aggregates of crocidohte, Cumberland, R. I
Arfvedsonite is usually in long prisms flattened parallel to oo P So (oio), but otherwise very much like hornblende. It m block or dark green and translucent, and has a dark bluish gi ay st rcaL It s hard- ness is 6 and density 3 4-3 5 rt 1S strongly plcochroic Thin splinters parallel to oopSb (oio), are olive giccn and those paialM to oo I>6b are deep greenish blue Its refractive indices for yellow light are:
05=1687, 0=1707, 7=i7°S
Before the blowpipe the mineral fuses easily to black magnetic globule and colors the flame yellow It is not acted upon by acids.
Riebeckite is found only in embedded prisms, showing no termina- tions It is black, vitreous and very plcochroic m gieen and dark blue tints Its density is about 3 3, and its hardness 5.5-6. Its reft active index for yellow light is about i 687. Before the blowpipe it fuses easily, imparting an intense yellow color to the flame.
Crocidohte is an asbestus-hke, lavender-blue or dark green nebeckitc, that contains a larger amount of iron, due to the presence of the mole- cule FeSiOa It occurs also in earthy masses. Itb st reak is lavender-blue or leek-green and its hardness is 4 In all cases it appears to be a secondary mineral, The green fibrous variety ib known as " catVeye."
Anhydrous Metasilicates 393
Both nebeckite and: rfvedsomte weather to aggregates of iron oxides, quartz and carbonates The decomposed, brown crocidolite is the well- known ornamental stone " tiger's-eye "
Occurrence and Localities — Arfvedsonite is found principally in igneous rocks rich in soda, especially the coarse, nephelme syenites of Greenland, Kola, Russia, and m the augite syenites of Norway. It occurs also in the nephelme syenites of Dungannon township, Ontario, and of the Trans-Pecos district, Texas
Riebeckite is also formed m acid locks nch in soda, such as certain giamtes, syenites, etc It is found on the Island of Socotia in the Indian Ocean, in fine-gramecl granitic locks at Ailsa Crag, Scotland, m Corsica and a few other places The crocidolite variety occurs in a clay slate on the banks of the Orange River in South Africa, at various pomts in the Vosges, Salzbuig, Tyrol and Andalusia, in Europe, in Templeton, Ontano, in veins at Beacon Pole Hill, near Cumberland, R I , m gran- ites at Quincy and Cape Anne, Mass , near St Peter's Dome, El Paso Co , Colorado, and as fibers in rocks at various other points m the United States,
Tr1Cun1C Amphibole
The only known tnclmic amphibole is the comparatively rare aenig- matite, an alkali amphibole with a complicated composition that may be represented by the formula Na4Feq(Al-Fe)2(Si Ti)12O3s The mineial occurs m very complex crystals, with noAiTo=66°, in alkdlinc rocks at Naujakasik, Greenland, m the Fourch Mts , Ark ; and at several other places
It is black, or brownish black, and translucent or transparent and has a reddish brown streak It is, moreover, strongly pleochroic m brownish black and reddish blown tints It is brittle, has a hardness of a little more than 5 and a density of 3 7-3 8 Before the blowpipe it fuses to a brownish black glass It is partly decomposed by acids It is distinguished from other dork hornblendes by the cleavage angle of 66°.
BASIC METASILICATES Kyamte ((A10)2SiO3)
Kyanite, cyamte, or disthene, is a fairly common product of meta- moiphisni in certain schists The name kyamte suggests the sky blue color noticed in many specimens The name disthene refers to the great difference in hardness exhibited m different directions.
The mineral is regarded as a basic metasihcate of the theoretical
Descriptive Mineralogy
composition 8102=3702, 203 6298 (compare pages 319, 320). Nearly all specimens contain a little FeaOs but otherwise they cor- respond very closely to the calculated composition indicated by the above formula A light blue specimen from North Thompson River, B C , upon analyses, gave
Fe203 CaO MgO Total
Si02
A1203
7=ioS044l'
J .
' a
FIG 210— -Kyamte Crys- tal with oo PQO, ioo (0),
oo POO, oio (ft), oP, ooi (c), co'P, 1 10 (Jf)f
oo P', no (m) and
00 P'2, 210 (I)'
Kyamte crystallizes m the system (luclinic piruicoiddl class), with an axial ratio 8991 i 709°* 9°° Si', 101° 2' and Very few crystals are well developed Their habit is columnar or tabular with oo P 66 (ioo) predomi- nating More frequently the mineral occurs in long, flat, isolated blades, or in diveigmg flat plates (Fig 210) Some crystals are very complex. Usually, however, only the forms oo Poo (ioo), ooPoo(oio), ooP'(no), oo'P2(2io)j oo'P(iTo) and oP(oor) arc pres- ent Twinning is common according to several laws, most of which, however, yield twins in which the basal planes (oP) of the twinned in- dividuals are parallel The most frequent twins have oo P 65 (ioo) as the twinning plane Other twinning planes are perpendicular to the axis c, or to the axis b The basal plane oP(ooi) also serves as the twinning plane m some cases Twinning is often repeated, producing lamellae crossing columnar crystals approximately parallel to the basal plane, and giving rise to a definite parting in this direction
The cleavage of kyamte is very perfect parallel to oop65(ioo) and less perfect parallel to co P 06 (oio) It frequently possesses also a parting parallel to oP(ooi), as already stated The luster on cleavage faces is pearly Otherwise it is glassy. The mineral is often blue in color, less frequently it is colorless or white, yellow, green, brown or gray It is translucent or transparent and the darker blue varieties are pleochroic m dark and light blue tints. Its hardness varies greatly on different faces and in different directions on the same face. On the macropmacoid a it is about 5 parallel to the vertical edges, and 7 in the direction at right angles to this The specific gravity of the mineral is about 36, and its refractive indices for yellow light are; a 2=1.71 71, l8=;i 7222,7=1.7290.
Before the blowpipe kyanite whitens, but otherwise it reacts like
Anhydrous Metasilicates
sillimamte It is insoluble m acids It is distinguished from the few other minerals that it resembles by the great differences in hardness on its cleavage surfaces At a high temperature (about 1350°) it appar- ently changes to silhmanite
Kyanite weathers to muscovite, talc (p 401) and pyrophylhte (p 406), and is itself an alteration product of andalusite and corundum
Synthesis — It is not known that the mineral has been produced in the laboratory
Occurrence and Origin —Kyanite occurs as large plates and small
FTO 2TT — Bladcrl Kyanito Crystals in a IV! u m cons Quart/, hist from PM/O Forno, hwiUcrlaml (About natural st/e )
crystals in micaceous and othei schists (Fig 211), and as an important constituent of some quarUites At Horrsjoborg, m Wermland, Sweden, it forms a distinct layer of schist several meters thick In a few places it is found m zones of contact metamorphism, but it is more frequently the result of dynamic metamorphism (cf p. 26).
Locates — Crystals have been found at Gremcr in the Tyrol, at Mte Campione in Switzerland, and at Graves Mt m Lincoln Co , Ga The mineral also occurs in fine plates at Chesterfield, Mass , at Litch- field, Conn,; at Bakersvillc, N. C, and on North Thompson River, B C , Canada
Uses — Transparent kyanite is sometimes used as a gem.
Descriptive Mineralogy
Calamine ((ZnOH)2SiO3)
Calamme, or hemimorplute, is an important ore of zinc It is one of the few silicates used as a source of metals While theoretically a pure zinc compound it usually contains a little FcjO? and ficquently small quantities of PbO In some cases it contains also a little carbon- ate A number of formulas have been suggested foi it, of which the one given above is the simplest According to several piommcnl mmei- alogists, howevei, the formula ZnaSiO4 HaO is prof ci able
Si02 FeoOj ZnO HjO Total
Theoretical 25 01 67 49 7 50 100 oo
WytheCo, Va 23 95 67 8S 8 H 99
Fnedensville, Pa 24 32 2 12 65 05 7 89 99 38
The mineral occurs in brilliant crystals that are orthoihomlnc and distinctly heniimorphic (rhombic pyramidal class), with an axial uitio
of 7834 i .4778 The crystals are usually tabular parallel to <*>P&(oio) Many ate highly modified but some are fairly sim- ple, with oo P(i 10) , oo P 66 (TOO) and 3? 05(301) m the pris- matic zone, 3Po6 (031), Poo (101), Poo (on) and oP(oot) at the ana- logue pole and P2(i2j) at the antilogue pole (Fig 212) The angle no A no 76° c/ Tunis are fanly common, with oP(ooi) the twinning plane Often many crystals sue grouped in sheaf-like, lilmms 01 warty aggiegates and in crusts The mineral is also granular and compact Its cleavage is perfect parallel to oo p(i 10)
Calamme is glassy, transparent or translucent, and when pure is colorless or white Usually, however, it is gray, yellow, brown, greenish or bluish Its streak is white, its hardness 4-4 5 and its density 3.2 3 5 It is brittle Its fracture is uneven The mineral is strongly pyroelec trie with the end of the crystals terminated by dome faces the analogue pole. In contact twins both ends are analogues. The mineral becomes phos- phorescent upon rubbing, and is fiuoiescent m ultra violet light. Its refractive indices for yellow light are ot- 1 6136, r 6170, 7=1 6360. Before the blowpipe calamme is almost infusible, but on charcoal it swells, colors the flame greenish and fuses with difficulty on the edges*
FIG 212 — Calamme Crystals with oo P, no (m), oo P56, 100 (a), >po6, oio (6), 2P*2, 12! (i)), Poo , 101 (A), Poo, on (e), 3P3oi Wi 3P, 031 (0 and oP, ooi (c)
Anhydrous Metasilicates 397
With soda it gives the zinc sublimate In the closed glass tube it de- crepitates and yields water and becomes cloudy Its powder dissolves in even weak acids with the production of gelatinous silica
Calamme is distinguished from smithsomte by its reaction with acids and from other minerals by its crystallization and reaction for zinc It alters to willemite, smithsomte and quartz Calamme has not been produced artificially
Occurrence — It occurs principally in the upper or oxidized zones of veins of zinc ore and in layers above the zone of permanent ground water in certain zinc and lead-bearing limestones It is associated with lead ores and various zinc compound and it often pseudomorphs calcite, galena and pyromorphite
Localities — Calamme occurs in nearly all places where zinc and lead ores arc found It is abundant at Altenberg near Aachen in Rhen- ish Prussia, at Wiesloch, in Baden, near Tamowitz, in Silesia, at Rezbanya, Hungary, near Bleiberg., Cannthia, near Santander, Spain, in Cumberland, England, at Sterling Hill, N J , at Fnedensville, near South Bethlehem, Penn , at the Bertha Mine in Pulaski Co , and at the Austin Mine, in Wythe Co , Va , and in the zinc-producing areas in the Mississippi Valley
Usett — It is a common a-bbociate of other zinc ores and many lead ores and is mined with the former as a source of zinc.
Acid Metasilicates
Serpentine Group
The serpentine group includes a large number of hydrous magnesium silicates that differ from one another mainly in the proportions of water present and m the ratio of silica to magnesia None of them yields crystals, though their crystallization is thought to be monoclmic All occur in dense fibrous or platy aggregates The most prominent mem- bers of the group are
Serpentine BUMgaSigOo, or Si02 MgO
H(MgOH),<(Si03)2 =43 'So 4346 1304
Meerschaum. . HUMgsSisO i o, or
H3Mg(MgOH) (8103)3 =60 83 27 01 12 16
Steatite . H2Mgij(SiOs)i "63 52 31 72 4 76
All are soft and nearly infusible, and all are of considerable economic importance.
398 Descriptive Mineralogy
Serpentine (H4Mg3Si2O9)
The substance known as serpentine may be two different minerals, one orthorhombic and the other monochmc They, however, cannot be distinguished, except by microscopic study Serpentine occurs in structureless, fibrous, foliated and schistose masses of a white, gray, brown or green color It is translucent and has a dull, slightly glistening or fatty luster, and a white streak The variety known as " noble ser- pentine" is nearly transparent and has a clear gieemsh or yellowish white, yellowish green, apple-green or dark green color The mineral, when pure, has a hardness of 3, but it frequently seems harder because there are often mixed with it tiny remnants of the much harder minerals from which it was derived The specific gravity of pure serpentine is 2 5-2 6 Its refractive indices vary widely /3= i 502-1 570
Serpentine fuses on thin edges when heated in the blowpipe flame It yields water in the closed tube When heated to about 1400° it crys- tallizes as olive It is decomposed by hydrochloric and sulphuric acids with the separation of gelatinous silica, which, m fibrous* varieties, retains the shapes of the fibers. It is also soluble in dilute carbonic acid Its powder reacts alkaline
Chrysolite is a silky, nearly transparent fibrous variety occurring in veins It is apparently orthorhombic.
Antigonte is a form occurring m laminated masses or in microscopic scales, that are possibly monochmc
Baltwnonte and ficrolite are coarse, green, fibrous varieties
Analyses of a pure green serpentine, and a typical chrysotde, both from Montville, N J , are quoted below
Si02 A1203 Fc203 FeO MgO CaO H2O Total
I 42 05 30 .10 42 57 05 14 66 99 73
Ii 42 42 63 62 . 41 01 15 64 100.55
I Green serpentine, Montville, N J II Chrysotile, Montville, N J Also 33 NiO.
Massive varieties are distinguished from tak by their solubility in acids and by differences m hardness, and chrysotile is distinguished from amphibok asbestus by the presence in it of water,
Synthesis.— Serpentine has been made by the action of a solution of Na2SiOs upon magnesite for 10 days at 100°.
Occurrence — The mineral is a common decomposition product of several other magnesium silicates, more particularly olivine, pyroxene
Anhydrous Metasilicates 399
and chondrodite Many igneous rocks rich in these minerals are com- pletely changed to serpentine, especially around their peripheries, and some metamorphosed limestones are also partially or completely ser- pentimzed It is probably a secondary mineral in all cases
Localities —Serpentine occurs in large quantity at Webster, N C , Montville, N J , Easton, Penn , at the Tilly Foster Iron Mine, Brewster, N. Y , at Thetford and Black Lake in the Eastern Townships of Quebec, and at many other places m North America, It is also known fiom many places in Europe
Uses — Serpentine when massive is used as a building stone The finer varieties are sawed into thin slabs and used for ornamental purposes Marble with streaks and spots of serpentine is known as ophicdcite and under the name "verd-antique " is employed as an ornamental stone. Mixtures of serpentine with other soft minerals are ground for a paper pulp The fibrous variety — chrysotile — is mined and sold under the name of asbestos, which, because of its fibrous structure, its flexibility, its incombustibility, and because it is a nonconductor of heat and electricity is becoming an exceedingly important economic product. It is woven into paper and boards that rrc used to cover steam pipes, and to increase electric insulations, and is manufactured into shingles It is used also in fireproofing, m the manufacture of automobile tires, in making paints, and as a substitute for rubber in packing steam pipes
Preparation — The chrysotile mined in Vermont comes from a mass of serpentine that its cut by many small veins of chrysotile The rock is crushed and the liber is separated by washing, or by some other mechan- ical method The pulp rock at Easton is a mass of serpentine, talc and a few other minerals It is ground and sixed for use in paper manu- facture
Production — Chrysotile is mined in Vermont and Wyoming. The production is rapidly increasing but the actual amount mined annually has not been disclosed. The total aggregate of chrysotile and amphibole asbestos (see p. 386), produced in the United States during 1912 was 4403 tons, valued at $87,959 The imports of unmanufactured asbestos for the same year were valued at $1,456,012, of which $1,441,475 worth came from Canada. The total production of this country m the same year amounted to about $2,979,384, most of which came from the Thet- ford district in Quebec. This is about 80 per cent of the world's pro- duction. The value of the serpentine used as an ornamental and build- ing btonc is not known,
MgO
A120 Fc203
H20
Total
S°
is ss
99
Is 83
400 Descriptive Mineralogy
Garnierite
Garmente may be regarded as a serpentine or talc in which a portion of the magnesium has been replaced by nickel, or possibly as a mixture of a colloidal magnesium silicate and a nickel compound Its impor- tance consists in the fact that it is the only commercial source of nickel aside from the pentlandite in the pyrrhotite of Sudbury, Canada. Three analyses of garmerite from New Caledonia follow.
Si02 NiO
35 45 4S Is
37 78 33 9i
42 61 21 91
These show that as MgO diminishes, NiO increases.
Garmerite is a dark green to pale green substance with many of the physical properties of serpentine Its luster is dull, or like that of var- nish It has a greasy feel, a hardness of 2-3 and a density of 2 3-2 8 Its streak is light green to white When touched to the tongue it ad- heres like clay It is infusible when heated before the blowpipe, but decrepitates and becomes magnetic. It is partly soluble in HCl and HN03
It is readily distinguished from malachite and chrywcolfa by its structure, its greasy feel and the absence of a good copper test.
Occurrence and Localities —The mineral occurs as earthy masses, as mamillary coatings and as impregnations and veins in serpentine. In all cases it appears to have resulted from the weathering of periclotite. The earthy masses are residual and the veins are deposits from down- ward percolating water that obtained nickel from the decomposing rock
The principal occurrences of garnierite are New Caledonia, where it is mined as a source of nickel, and at Riddles, Douglas Co,, Oregon, A very closely allied species, genthite, occurs associated with chromitc in serpentine at Texas, Lancaster Co,, Perm., at Webster, N. C., at Malaga, in Spain, and at a few other places
Production — Garniente is mined from 40 mines on the plateau of Thio, New Caledonia, at the rate of about 130,000 tons annually of a per cent ore. In 1912 there were produced 72,315 tons of ore and 5,097 tons of matte containing 2,263 tons nickeL The aggregate value of ore and matte was about $1,140,000,
Anhydrous Metahiijcates 401
Meerschaum (H4Mg2Si3Oio)
Meerschaum, or scpiohte, occurs as a massive, dense, earthy aggre gate of a white, yellowish or reddish color, and also as a finely fibrous, crystalline aggregate (parade piohte) It is opaque, has a conchoidal fracture and a shining white streak Its hardness is 2 and density about 2 Dry specimens will float on water, because they are not easily wet When touched to the tongue a clinging sensation is pro- duced Two varieties of the commercial material have been recognized Of these, one, a sepiohte, is HsMSiaOi*) and the other j8 sepiolite, has the composition indicated above
The analyses of white meerschaum irom Asia Minor and from Utah gave the following results
Al20j Fe20j MgO H2O Total
Asia Minor 52 4$ 80 23 25 23 50 100 oo
Utah 52 97 86 70 22 50 18 70 99 74
Of this 8 80% was driven off at 100°, Included also tire 3 14 Mn20j and 87 CuO
Before the blowpipe the mineral fuses on its edges to a white enamel Often, at first, it tuins brown 01 black and then, upon higher heating, it bleaches to white At low temperatine in the ebbed tube it yields a little hygiostopic water. At high temperature water is given off fieely The mineral dissolves m hydicx hlouc auci, with the production of gelat- inous silica m the case of theot variety
Meerschaum resembles chalk and kaolin, from which it is easily dis- tinguished by treatment with hydrochloric acid.
Occurrence and Localities — The mineral is found as nodules in young sedimentary beds in Asia Minor, where it is associated with magnesite. Both minerals are believed to be alteration products of serpentine It occurs also with opal at Thebes, Greece. A iccl variety occurs in lime- stone at Qumcy, France, and a green and white variety forms a small vein m a silver ore in Utah In nil of its occurrences it seems to be secondary
Cfre— -Mecrathaum is used for carving into ornaments and pipes.
Steatite (HaMgaCSiOaM
Steatite, or talc, usually occurs in flaky, foliated and massive forms, and in plates that appear to be tabular crystals with hexagonal outlines, It also forms, with chlorite and a few other substances, the rock soap- stone. Although its crystallisation is unknown, because of the close
402 Descriptive Mineralogy
analogy between its physical properties and those of chlorite and the micas its symmetry is believed to be monoclmic
The composition of pure white talc and ordinary soapstone are shown by the two analyses below
White tile Soapstone
Urserenthal, Switrerlanil W Gnqualand, Africa
Si02 o° 85 63 29
A1203 i 7i 24
Fe203
FeO 09
MgO 32 08
H20 4 9S
Total 99 68 100 90
The composition corresponding to the formula HjMgSiOa)! is- Si02=63 5, MgO=3i 7 and H30=4 8
The cleavage of talc is well marked and on its cleavage surfaces its luster is pearly Its cleavage plates arc flexible The mineral is white, gray, greenish or bluish, and is transparent or ti anslucent The massive forms, known as soapstone, aie white, gicenish, yellowish, red or brown All varieties are soft— the mineral being chosen to represent r m the scale of hardness — and all have a soapy feeling The density of pure talc is 2 6-2 8 For yellow light, a— i (530, i 589, i 1589.
Before the blowpipe the mineral exfoliates, hardens and glows brightly, but it is nearly infusible (fusing temperature is about 150°), melting only on the thinnest edges to a white enamel. It yields water in the closed tube only at a high temperatuie. It is unattacked by acids before and after heating Its powder reacts alkaline.
It is distinguished from other white, soft minerals by its softness, its insolubility in acids and its infusibihty
Occurrence — The mineral is a common alteration product of other magnesium silicates, often pseudomorphing them. Thus, pseudo- morphs of the mineral after actmolite, Imnuite and siihlite are common Pseudomorphs after pectolite, dolomite and quarto are also known. In. these forms it is secondary.
It occurs also m marbles and other crystalline rocks, where it was produced by regional metamorphism, It is found, further, as small veins cutting serpentine and metamorphosed limestones, as layers under the name of talc schists, associated with other schistose rocks and as massive aggregates of finely matted fibers, probably resulting from the alteration of basic igneous rocks The last described variety is the rock soapstone.
Anhydrous Metasilicates 403
The vein material is usually white, fibrous and pure It is gi< und and placed on the market as talc The impure ai icty (soapstone) is sawn into blocks and boards
Localities — Talc and soapstone occur at many places Good white platy talc occurs at Lampersdorf, in Silesia, near Piessnit?, m Bohemia, near Mautern, m Steiermark, at Andermatt, in Switzeiland, at Russell, Gouverneur and other points m New York, at Webster, N C , and at Easton, Penn
U$e\ — Ground talc is extensively used as a lubricator, m the manu- facture of papci, as a fillci m curtains, cloth, etc , as a foundry facing, in the manufacture of molded rubber goods, ub a toilet powder, as a polish- ing material, as a pigment, in the manufacture of gas tips, pencils, cray- ons, etc Soapstone is sawn and used as linings of acid vats and laundry tubs, and in the manufacture of table tops, sinks, etc , in chemical labora- tories Because of itb nonabsorbent qualities it is also being used largely in electric switchboards. Its various uses are due to its softness, mfusibility, and its power of resistance to the attacks of acids
Production. — The principal sources of talc and soapstone m the United States are m a belt on the east side of the Appalachians ex- tending from Vermont to Georgia Largest producers m 1912 were:
Virginia, wilh a production of 25,313 tons, valued at $576,473, New York, with a production of 66,867 tons, valued at $656,270, Vermont, with a pioduclion of 42,413 tons, valued at $275,679
Of the aggregate of 159,270 tons, valued at $1,706,963 produced m 1912, 15,510 tont. were sold in the rough for $66,798, 2,642 tons, sawed into slabs, were sold for $50,334, 21,557 tons were manufactured and sold for $600,105, and 119,561 tons were sold ground for $989,726. Of this aggregate 133,289 tons, valued at $1,097,483 were talc and 25,981 tons, valued ai. $609,480 were soapstone In addition to the home produc- tion, there were also consumed in the United States 10,989 tons of high- grade talc, valued at $122,956, which was imported,
Kaolin1Tk Group
The kuohnitc group of minerals comprises hydrous aluminium sili- cates corresponding to the magnesium silicates of the serpentine group The principal members of the group are*
Kaohmte, HiAbSfeOo, or H2Al(Al(OH)3)a(Si03)4
=346,50 Si02, 39 S6 94 H20 Pyrophyllite, HzA,h(SiQz)4 66,65 SiOa, 28 35 AlsOs, 5 oo H20
404 Descriptive Mineralogy
Kaolmite corresponds to serpentine in which all the Mg has been re- placed by Al and pyrophyllite to steatite In addition to these, there are other closely related compounds which may be intei mediate in com- position between these two Among them the most common arc allo- phbne, montmonllonite and hallo
Both minerals are of economic importance Kaohmte is the base of all clay products like pottery, tile, , etc
Kaolinite
The crystallization of kaohnile is piobably jnonoc hnu The crystals, which are rare, are thin plates with an hexagonal habit, bounded by the planes oP(ooi), ooP(no) and (oio) and +P(7ii). Thou axial ratio is 5748 ' i : i 5997 with £=83° n'. Their cleavage is peifect parallel to the base
Distinct crystals have been found only on the Island of Anglesey, Wales, and at the National Belle Mine, at Silveiton, Colo , wheie they comprise a white powder every grain of which is a crystal
The mineral, when pure, is white or colorless and transparent. It has a hardness of i and a specific gravity of 2 45 It is infusible before the blowpipe and is only slightly attacked by HC1 It is decomposed by alkalies and alkaline carbonates with the production of hydratcd silicates Its index of refi action is about i 56.
The greater part of the kaolmite known is not in nystuls ft usually occurs in foliated or dense earthy masses to which various names have been assigned
Naknte is a white crystalline mass of kaolmite made up of tiny flakes often arranged in fan-like or divergent groups. The individual flakes have a pearly lustei It occurs as vein lillmgs in certain ore- bodies
St&nmarkite is a dense mass of microscopic grains often forming nodular masses and occurring as veins ancl nests in rocks. It is harrier than pure kaolin (H— 2-3), and is often yellowish, gray or reel in color
Kaohn is an earthy, friable mass of flaky kaolmite which when moist becomes plastic, and, therefore, of great value in the manufacture of pottery It is more soluble in acids than the crystallised variety. It fuses at about 1780°
Kaolin is distinguished from chalk by its reaction toward HC1, from meerschaum and talc by the reaction for Al with Co (NO;*) a, and front mfusional earth by the fact that its powder will not scratch glass,
Clay is a mixture of kaolinite, quartz, fragments of other mineral
Anhydeous Metasilicates 405
particles and various decomposition products of kaohmte and other silicates, among the most important being various colloidal, hydrous, aluminous silicates and magnesium and calcium carbonates The gieater the proportion of colloidal material in the clay the more plastic it is and the more valuable lor manufacturing purposes Different clays have received diffei ent names which indicate in a way their uses Among the most impoitant of these arc
China day, a very puie, white kaolin, Ball day, a white, very plastic clay, Fje day, a fanly pure clay capable of resisting great heat, Flint day, a hard clay which is not plastic even after grinding, Brick day, an impure clay suitable foi making brick, Pottety day, stoneware clay, terracotta day, etc , are jU impure clays that are adapted to the uses suggested by their names
Sample analyses of kaohmte and of some of the purer clays follow
F Total IS ioo n 100 oo
Si02 AbOa FcsOj CaO Nd20
HjO
I 46 35 39 59 ii IS
Ii 46 86 39 24
III 43 46 41 48 i 20 37
IV 59 92 27 56 i 03 tr. ,64
F Crystals Fiom National IH!e Mine, Colo
II Kaolin, SuliU, near Meissen, Saxony
Til Slemmfiikile, hlaKgcnwalil, Hohc-muu
IV Flint lire i lay, Salmeville, Ohio.
NujO+KjQ
Occurrence— Kaohmte occurs in feldspathic rocks near ore veins, Here it was foimccl partly by ascending magmalic solutions and partly by descending IIgS04, produced by the oxidation of the sulphides In the uppci poi lions of the veins Most kaolin, however, is a weathering product of feldspar (see p. 408), and of feldspathic rocks. When acted upon by water, and more particularly by water containing dis- solved CDs, the feldspars lose alkalies, calcium and some silica, leaving an aluminium silicate behind. Thus, for the potash feldspar orthoclase.
AlaO,* 6SiOi( KAlBLAt) - KaO 48102 Al20;j sSiOu, which with (kaolimte).
Other silicates also yield kaohmte on weathering— in some cases completely changing so as to yield pseudoinorphs of kaolin.
Very complete weathering of this kind takes place in bogs, and
406 Descriptive Mineralogy
some of the best known beds of kaolin arc believed to have been formed at the bottoms of peat bogs
Locakhes — Kaohnite in measurable crystals occurs only at the two localities that have already been mentioned The puic, white, dense kaolin is fairly widely spread Clay occuis almost um\ci sally The principal localities of kaolin in North America aie near Jacksonville, Ala , Mt Savage, Md , various points in Tennessee, Noith Carolina, Illinois, Missouri, New Jersey and Pennsylvania
Production— The total value of clay products manufacluiccl in the United States during 1912 was over $172,800,000, of which by far the largest part is represented by common brick, of which $51,706,000 worth were made Pottery followed with an output valued at $3 6 , 504,000 It is not possible to estimate the value of the clay represented in the man- ufactured product because in most cases the manufactui CM s mine their own clay and make no account of the raw material The quantity of clay mined m the United States and sold to manufacturer during 1012 amounted to 2,530,000 tons, valued at $3,946,000, In 'addition, there were imported 334,655 tons of clay, valued at $1,952,000
Pyrophyllite (H2Al2(SiO,j)4)
Pyrophylhte nearly always occurs m groups of radiating 01 diveigmg fibers that are either orthorhombic or monochmc in crystallisation It may be isomorphous with steatite. The bundles of libers derive easily into flexible sheets that have a pearly luster on their cleavage faces When pure the mineral is light-colored m shades of yellow, gray 01 green It is transparent or translucent and has a greasy feel Dense, struc- tureless masses are known as agalmatohte.
The mineral is very soft, about i Its density is 2.8 or 2,0 Before the blowpipe it melts on the edges to a white enamel and fibrous varieties exfoliate and swell Heated m the closed tube pyrophyllite assumes a silvery luster and gives off water. It is only partially soluble in IIC1, but is completely decomposed by Na2COs*
It is best distinguished from ta'c by the reaction for aluminium,
Synthesis —Upon heating to 3oo°-soo° a mixture of SiOs>, AliAt and potassium silicate a mass is obtained which consists of aiulalusite, muscovite and pyrophyllite
Occurrence and locator —Pyrophyllite is found at a number of points m many different associations, where it is probably the result of weathering of other silicates Its principal localities in the United States are Graves Mt., Ga., Cotton Stone Mt., Deep River, Cur-
Anhydrous Metasilicates 407
bonton and Glenclon, N C , Chesterfield, S C , and Mahanoy City, Penn
Uses — The massive form of the mineral is used to some extent in making slate pencils, and for the other purpose for which talc is employed Agalmatohte is used by the Chinese as a medium from which they carve small images
Chapter Xviii
Tim SI LIC ATKS— t ontmmd
The Anhydrous Trimetasilicates
The Feldspars
THE feldspars are among the most impoitanl ol .ill mineials They are abundant as constituents of many igneous locks and in mixtures filling veins Their principal scientific impoitaiuo lies in the fact that they indicate by their composition the nature of the lock magmas from which they crystallize Consequently, in some systems of rock classi- fication the grouping of the rocks is based primarily upon the presence or absence of feldspar, and the naming of the fddsputhie rocks is in accordance with the nature of their most prominent feldspathic con- stituent Moreover, some of the feldspars aie of economic importance.
Chemically, the feldspars may be regarded as isomorphous mixtures of the four compounds, KAlSuONaAlSiiOs, NajAlAlSioOs, CoAlAlSiaO and BaALAlSiaOs, each of which, except the third, has been found nearly pure in nature as orthoclase and murodme, barhimlt* and Mite, an- orthite and The third, Na2AlAlSioOs, has been mule m the laboratory, but it occurs in nature only in isomorphous mixtures with the anorthite and albite molecules The pure compound has been called carnegete and its mixtures anemomitn The feldspars have also been regarded as salts of the acid HftAlSigOx in which the hy- drogen is replaced by various radicals, thus. (KSi)AlSijjOK, orthodase; (NaSi)AlSi208, albite, (CaAlJAlSiaOg, anorthite, and (BaAl)AlSijOs, celsian
The potash molecule crystallines fiom magmas containing potas- sium, sodium and calcium, but it also frequently forms isomorphous mixtUres with the soda molecule and in some cases with the barium molecule Mixtures of the potash and calcium molecules are e\- tremely rare as minerals, but they have been formed experimentally in the laboratory The albite and the calcium molecules are usually intermixed Both are known in a nearly pure condition an minerals, but their mixtures are much more common Indeed they are BO common that they are separated from the other feldspars and formed into a clh-
Anhydrous Trimetasilicates 409
tinct subgroup under the name of the plagwdaw group, with albite and anorthite as the two end members The plagioclases constitute the best known isomorphous series of compounds in the realm of mineralogy.
The calculated compositions of pure orthoclase (or microclme), albite, anorthite and celsian with their specific gravities are
K20 Na20 CaO BaO Sp Gr
Orthoclasc 64 7 18 4 16 9 2 55
Albite 68 7 TO 5 u 8 2 61
Anorthite 43 2 36 7 20 i 2 76
Celsian 32 o 27 2 41 8 3 34
All the feldspars aic trichnic, but the pure potassium and sodium com- pounds, in addition to possessing distinct trichnic phases (micioclme and albite) occur also in crystals which, because of sub-microscopic twinning, (p 420) are apparently monochnic (oithoclase and barbiente) Usually the forms on orthoclasc arc designated by symbols that refer to the monoclmic a\es, but since the habits of all feldspars are the same they can be as readily understood when referred to the tnclimc axes The crystallographic constants for the members of the group that consist of unmixed molecules are
7 Anglc(ooi)A(oio)
Celsian
657 :
i :
90°
2'
90°
Albite
i
3'
29'
88°
9'
Anorthite
.6347 :
i '
1.3'
S3'
9i°
12'
90°
86° 24' 85° 50'
The simple crystals of feldspar exhibit three habits, but on nearly all the same forms occur. These are oP(ooi), ooP 06(010), ooP'(no), oo'P(no), /P/ oo (101), 2/Py oo (201) and less commonly s/P' 00(021), 2'Py & (QJ i), oo P/3(i3o), oo /P3(i3o), /P(I n), P/(i7i) and oo P 60 (100) In orthodase and the other apparently monochnic forms these symbols may be written oP, coPob, oo P, p*, 2Poo, 2P5b, oopj, P and oo poo (Figs. 213 and 214). There have, moreover, been reported on orthoclasc about oo other planes and on the plagioclases about 45;. Of these, however, a number are probably vicinal, as they have extremely large indices,
The principal habits are the equidimensional, the columnar (Fig. 213), and the tabular (Fig. 214) The tabular crystals are usually flattened parallel to oio The columnar forms are elongated parallel to the c or the a axes
Descriptive Mineralogy
Twinning is common, according to five laws, and much less common according to several others Of the five common laws three apply to all the feldspars, and the remaining two to the tnclimc types alone The first three are the Carlsbad, the Manebach and the Baveno The other two are the albite and the penclme
In Carlsbad twins, 100 is the twinning plane and usually oio is the
%
Fig 213 Fig 214
FIG 213 —Orthoclase Crystals with oo P, no (m), w P w , oio (ft), oP, OOT (c) and
aP 55 , 201 (y)
FIG 214 —Orthoclase Crystals with m, b, c and y as m Fig 213 Albo P oo , loi (c), P, in (0), oo P3 , 130 (a) and 2P 2b , 021
\zw
Fig 216
Fig 215
FIG 215 Carlsbad Interpenctration Twins of Orthoclase Twinning plane ia 00 P
(100), composition face ooPw (oio) FIG 216 —Contact Twin of Orthoclase According to the Carlsbad Law.
composition face. The twinned parts may interpenetrate, as is usually the case (Fig 215), or they may he side by side forming a contact twin (Fig 216) If m the contact twins the planes Tot and ooi are equally prominent, since they are nearly equally inclined to the c axis the twin may be mistaken for a simple crystal (Fig. 216), In rare cases the composition face is 100 and the twinned parts are in contact,
Anhydrous Tbimetahilicates
The Baveno twins are contact twins, with 021 the twinning and com- position planes (Fig 217) As the individuals are elongated parallel to the a axis the result of the twinning is a square prism with its ends crossed by a diagonal that separates the same forms on the two twinned individuals In some cases the twinning is repeated and a fourlmg results
In Manebach twins, the twinning and composition plane is ooi These usually occur m columnar crystals elongated parallel to 0, or in tabular crystals flattened parallel to ooi or oio (Fig 218)
Ccirlsbad, Baveno and Manebach twins, as has been stated, are com- mon to feldspars of both the monochmc and tnclmic phases, but the penclme and albite laws are found only in the tnclmic types The
Fig 217
Fig 218
FK, 217 — -lUveno Twin of Orthoclasc Twinning and composition plane, aP ob (021) Fid 218- M iintbiu h Twin of Orlhoi Use Twinning and composition plane, oP(ooi)
description of these is, therefore, deferred until the plagioclases are
CUSSed.
Besides occurring in crystals, nearly all the feldspars are known also m gianular and platy masses
The pure feldspars are coloileas and transparent or translucent, and all have a glassy luster which, on cleavage faces sometimes approaches pearly As usually found, the feldspars are white, pink, reddish, yellow- ish, gray, bluish or green Some specimens show a bluish white shimmer or opalescence (moonstone), and others a reddish spaikle (sunstonc), due to enclosures of other minerals or of lamellae of a different refractive index from that of the mam portion of the mass All have u white streak All possess a very perfect cleavage parallel to the base (ooi) and a scarcely less perfect one parallel to oio Their fracture is uneven to conchoitlal, and hardness 6
Befoie the blowpipe fragments of the potash, barium, and calcium
412 Descriptive Mineralogy
feldspars are very difficultly fusible on their edges to a porous glass The soda feldspars are a little more easily fusible The fusing tempera- ture of albite is between 1200° and 1250°, that of orthoclase approxi- mately 1300°, and that of anorthite 1532° Anorthite is soluble in hydrochloric acid with the production of gelatinous silica. The other three feldspars are insoluble
The feldspars are distinguished from othei minerals by their crys- tallization, their two nearly perfect cleavages approximately perpen- dicular to one another, and their hardness They are distinguished from one another by characters that will be indicated in the descriptions of the several varieties
Feldspars rich in orthoclase and soda weathei fanly leadily to mus- covite, or kaolin and quartz The soda feldspars in some cases change to zeolites (p 445). With the addition of the calcium molecule calcite is often found in the weathering products. Under certain conditions, especially when in rocks containing magnesium and iion rmncuils, the calcium feldspars often change to a mixture of zoisite and albite, 01 a mixture of these with garnet, chlorite (p 428), epidote and otlici com- pounds This mixture is often designated by the name &an\
Syntheses —All crystals of the feldspars, except those of pure albite and pure orthoclase (including microchnc), have been made by slowly cooling a dry fusion of their components m open cuinbles Albitc and orthoclase have been produced from similar fusions to tungstic acid, alkah-tungstates or phosphates, or alkali-fluoride ha\r been a dried They have also been produced with quart/ by fusion m the presence of moisture in closed tubes
Occurrence and origm — All except the barium feldspars occur as important constituents of most igneous and of many metamorphic rocks. They occur also abundantly in a few sandstones (sirkoses) and m a few water-deposited veins, and are found mound a few volcanic craters as products of gaseous exhalations The barium feldspars are rare They have been seen only in dolomite associated with Imnte and tourmaline, in manganese ores and manganese epidote, and intergrown with albite in a pegmatite at Blue Hill, Delaware Co , Pa
Witih. respect to origin feldspars may be primary separations from a magma, primary deposits from solutions, pneumatotytie deposits, or they may be the result of metasomatic process. They are common products of contact and regional metamorphism
Uses —The feldspars, though extremely abundant, have compara- tively few uses In the future the potash varieties may become a source of the potash salts used in the manufacture of fertilizers. At
Anhydrous Trimetasilicates 413
present the principal use of the feldspars is in the manufacture of por- celain and other white pottery products and enamel ware They are used as fluxes to bind together the grains of emery and carborundum in the making of grinding and cutting wheels, and are employed also in the manufacture of opalescent glass, artificial teeth, scouring soaps and " ready roofing "
Production — All the feldspar used in commerce comes from pegma- tites The total quantity produced for all purposes in the United States during 1912 amounted to 86,572 tons, valued at $520,562. Of this, 26,462 tons were sold crude at a value of $89,001 and the balance ground The principal varieties mined are orthoclase, microchne and albite, though ohgoclase (a plagioclase rich m soda) is mined in small quantity.
Alkali Feldspars
Orthockse and Microcline (KAlSbO?) Barbierite and Albite
Orthoclase and microchne have the same chemical composition Both are potash feldspars, but both may contain sodium On the other hand barbiente and albite are both essentially soda feldspars but both usually contain some potassium In orthoclase the sodium is due to the admixture of the barbiente molecule, and m microchne to the presence of the albite molecule The soda-rich microchne is gen- erally known as anorthodase. The pure barbiente is not known to exibt as a mineral Analyses of these four varieties follow
SiO2 AlaO,i CnO K20 Na20 HjjO Total
I 63 80 21 00 13 80 I 40 Ioo 00
II 65 23 19 315 76 o 31 4 152 27 loo 00
TIT 67 oo 10 12 78 i 15 ii 74 . QQ 70
IV 66 18 IQ 52 36 13 03 01 ioo oo
V 67 99 19 27 7<5 3 o5 6 23 oo 09 03
Vi. 68 ?8 10 62 31 39 10 81 09 99,82
T OrthocUsc, Aclularia, Elba
II Soda-orthoclase, JDrachenfels, Prussia, Also ,56 BaO. lit. Burbiente, KrajjjcrtS, Norway IV. Microclmc, Ersby, Pargas, Finland.
V Anorthoclase, from granite, Kekequabic Lake, Mmn Also 82 FcjOj and
trace of MgO VI, Albite, from htchfieldile, Likhfiold, Maine. Also .23 FO and .09 MgO,
Albite is described among the plagioclascs (p, 418),
Descriptive Mineralogy
The most noticeable difference between orthoclase and miciocline is that the latter shows clearly its tnchnic symmetry by its twinning,
FIG 219— Section of Microclme Viewed between Crossed Nicols The grating structure indicates twinning ( ifltv Rownbmck )
and its optical properties, while in orthoclisc the twinning is so minute as to be unobservable and the op1 ical properties arc similar to those of monochmc crystals This difference is best exhibited in thin sections when viewed m polaroed light under the microscope Under these conditions certain sec- tions of microclme exhibit series of light and dark bars crossing one another perpendicularly (Fig, 219), while sections of orthoclase do not. The grating structure is due to repeated twinning according to the albite and pericline laws at the same time (p 419). If this method of twinning is present in orthoclase the lamellae are so minute that they cannot be seen even under high powers of the microscope
Several names that refer to more or less dis- tinct varieties of the potash feldspars are in com- mon use The most important are*
FIG 220 — Adulana Crystal with m, b, c, s and x as m Figs 2x3 and 214 Also fP 55, 203 fo)
Adularia, a nearly pure orthoclase, that is nearly transparent, occur- ring in veins Its crystals have the characteristic habit illustrated in
Fig 220
Anhydrous Trimetasilicates 415
Samdtne, a glassy soda orthoclase, occurring as large crystals often flattened parallel to oio, embedded in lavas
Moonstone, a translucent adulana, exhibiting a pearly luster, with a very slight play of colors
Sunstone, a translucent variety exhibiting reddish flashes from inclusions of mica, or other platy minerals
Perthtte, parallel mtergrowths of thin lamellae of orthoclase and albite
Microchne-perthite* parallel mtergrowths of lamellae of microclme and albite
Oithoclase and the other pseudomonoclmic feldspars may be dis- tinguished from the distinctly tnclmic forms by the value of the cleavage angle which in orthoclase is 90°, and in the tnclmic forms about 86°, except in microclme (See p 409 ) The value of the angle noAio 61° 13' in orthoclase Its refractive indices for yellow light are. oj=i 519, #=i 524, 7=1 526 With the admixture of the albite mole- cule these values increase The sp gr of pure orthoclase is 2 55 and its fusing point a little higher than that of albite (see p. 412)
Oithoclase may be distinguished from the other pseudomonoclimc feldspars by its specific gravity and the flame reaction
Syntheses — Crystals of orthoclase have been made by fusing SiOa and AkO* with potassium wolframate, vanadale or phosphate Also by heating aluminium silicate with a solution of potassium silicate and KOH in a tube at 100°, and by heating muscovite in a solution of potassium silicate at 600°
Occurrence — The potash feldspars are essential constituents of the igneous rocks — granite, syenites, rhyohtes and trachytes — and of some crystalline schists, and are accessory components of a number of other rocks They occur in most pegmatite dikes and as gangues in some ore veins, and m many contact metamorphosed rocks
Localities* — The potash feldspars are so widely spread that an enu- meration of their important occurrences is here impossible The best known localities of orthoclase are Cunnersdorf, Silesia, Drachenfels and Lake Laach, Rhenish Prussia (samdme), in the Ziller thai, Tyrol (adulana) , at St Gothard in the Alps (adularia) ; at Baveno, Italy, and at Mt Antcro, Chaffee Co , Col Microclme crystals arc well developed at Stnegau, Silesia; in the pegmatite dikes of southern Nor- way; and at Pike's Peak, Col (amcutomte). Anorthoclase occurs at Tyveholmen and other points in Norway and in the lava of Kilimand- jaro, Africa, and in that on Pantdlena, an island near Sicily. In North America pegmatites are abundant in" southeastern Canada, in
416 Descriptive Mineralogy
New England and in the Piedmont plateau area immediately east of the Appalachian Mts , and throughout this district all forms of the opaque potash feldspars are abundant Soda-potash feldspars ha\e been described from many places, but whether they j,ic soda orthoclase or anortholcase has rarely been determined
All phases of the alkali feldspars occur as components of igneous and metamorphic rocks
Potash-Barium Feldspars
The feldspars containing potassium and barium comprise an iso- morphous series with orthoclase and celsian as the two end members as follows
Sp Or
Ortioclase (Or) KAlSi308 2 55
Barium orthoclase OrjCei— OrjoCei 2 503-2 645
Hyalophane Or-iCei-OrrCi 2 725-2 818
Cdsim (Ce) BaAl2(SiOi)2 3 384
The chemical composition of some of the barium feldspars are illus- trated by the analyses quoted below
Si02 A1203 BaO CaO MgO K20 Na2O HaO Total
I 51 68 21 85 16 38 10 09 . 100 oo
Ii 52 67 21 12 15 05 46 04 7 82 2 14 58 99 88
III. 53 53 23 33 7 30 3 23 n 71 . 99 xo
IV. 54 15 29 60 i 26 i oo i 52 12 47 .. ioo oo I Theoretical for Or2Cei
II Bmnenthal, Tyrol
III Jakobsberg, Sweden
IV Sjogrufran, Sweden.
The minerals are isomorphous with orthoclase (with the possible exception of celsian, which may exhibit the triclmic habit and may more properly be isomorphous with microchmc), and their axial constants tire intermediate between those of orthoclase and celsian. The a\ial ratio for hyalophane is 6584.1 5512 01=90°, 115° 35', 7 00° Its cleavage angles are 90° Its crystals, as a rule, have the udularia habit. The Indices of refraction of the barium feldspars are:
Barmm-orthoclase (OrioCei) i 5201 i 5240 i 5257
Hyalophane (OnCei) i 5373 r 539S i 5416
Hyalophane (Or7Ce3) i 5419 i 5419 i 5469
Celsian i 5837 i 5886 i 5940
Anhydrous Trimetasilicates 417
These feldspars are rare They ha\ e been found only m metamor- phosed dolomites in the Binnenthal, Valais, at the manganese mines at Jakobsberg and Sjogrufran, Sweden, and mtergrown with albite m a pegmatite at Blue Hill, Delaware Co , Penn
Soda-Lime Feldspars
Plagioclase is the general name given to the group of isomorphous feldspars of which albite and anorthite are the end members The albite and anorthite molecules are isomorphous in all proportions and the physical properties of the mixed crystals accord completely with their composition Certain mixtures are much more common than others These were given individual names before it was recognized that they were merely members of an isomorphous series and these names were later applied to mixtures of definite compositions The names and the compositions of the mixtures corresponding to them are given in the following table
Si02 AbOs Na20 CaO Sp Gr
Albite NaAlSiaOsCAb) 68 7 19 5 n 8 2 605
Ab(,Ani 1 64 9 22 i 10 o 30
J 62 o 24 o 87 53 2 649
Ab]Ant I 55 6 28 3 57 10 4 2 679
AbjAni ]
AbiAnj f 49 3 32 6 2 8 3 2 708
AbiAnfJ I
AbiAn(J 46 6 34 4 i 6 17 4 2 742
Anorthite CdAlSiCXjMAn) 43 2 36 7 20 i 2 765
Qligodase Andenne Labrador ite Bytotvmte
Nearly all plagioclases contain small traces of K20, MgO and Fc20s, but otherwise their composition is nearly in accord with that demanded by their symbols, so that if one constituent is known the others may be calculated Moreover, the accord between physical properties and composition is so close tlut from the former the latter may be de- termined
Many oligoclascs, however, contain a large admktuie of the micro- clinc molecule so that they contain a notable quantity of KsO These are known as potadi-oligodc&e and are represented by the feldspar in a lock at Tyveholmen, Norway, the composition of which is as follows
SiOa AlaOn FcaOs CaO MgO K20 Na20 H20 Total 59 50 22,69 2 47 S °S tr. 2 50 6 38 i 37 100 37
418 Descriptive Mineralogy
Some authors limit the name anorthodase to feldspars of this kind and designate the trichmc soda-potash feldspar as soda-microclme
There is another group of soda-lime feldspars m which the anorthite molecule and an analogous sodic molecule (Na2Alo(SiCh)2) form iso- morphous mixtures The pure sodic molecule has not been found among minerals, but it has been prepared synthetically at temperatures above 1248°, under the name carnegieite Its sp gr 2 513 and its refractive indices for yellow light are a=i 509, 7=i SH Although not known to exist independently it is believed to be present m the feldspar of Lmosa, near Turns, and possibly in other feldspars that have hitherto been described as plagioclases If future work establishes the fact that there is a distinct series of feldspars composed of isomorphous mixtures of anorthite and carnegieite it is proposed to name the group anemouute to distinguish it from the plagioclase group which comprises isomoiphous mixtures of anorthite and albite
The Lmosa feldspar has properties nearly like those of the plagioclase AbiAm but its analysis yields the results m line I. The composition of is given in line II
Si02
A1203
CaO
Na20
K20
Sp Gr
oo
Ii
The
All the plagioclases have a habit, which is best expressed by the value of the angle between their cleavages, which are parallel to the planes ooi and oio The crystal constants of some of the common mixtures and the values of their cleavage angles are given in the table below.
Albite a : 6 : 6335 ' i SS77 94° 3' "6° 29' Q' 86° 24'
Ohgoclase. -6321 i ' 55*4 93° 4' n6° 23' 90° 5' 86° 32'
Andesme 6357 - i 55*1 93° 23' "6° 29' 89° 59' 86° 14'
Labradonte - 6377 : i : 5547 93° 3*' "6° 3' 9° 55' 86° V
Bytownite
Crystals of the soda-rich plagioclases are rich m forms, but those of anorthite and the hme-nch members are much simpler Albite crystals are usually tabular parallel to oo P 06 (oio) and elongated parallel to c or a Others are elongated parallel to b (Fig. aai), Ohgoclase ib
Anhydrous Trimetasilicates
more frequently columnar parallel to c, andesme tabular parallel to oo P So (oio) or oP(ooi), and labradorite and bytownite tabular parallel to oo P 06 (oio) Twins are e\en more common than among the potash feldspars Carlsbad (Fig 222), Manebach and Ba- veno twins are not uncom- mon, but more frequent than these are the twins after two laws that are impossible in the feld- spars with a monoclinic habit The two most common twinning laws among the plagioclases are the albite and the pcncline laws
In the albite law the twinning plane is oo P66 (oio) and the com- position plane the same (Fig 223) The twinning is usually repeated many times so that apparently homogeneous crystals may be built up of numerous lamellae parcel to oio Since the angle between oio and
FK, 221— Albite Crystals with oo'p, no co P'? no (/;/), oo P oo , oio (&), oP, oor (c) and
;Py CO , Toi (l)
Fie, 222
Fro 222 — Albite Twinned about oopcoj 100 Composition fate ool*oo,oro, Carlsbad law Compare Fig 316
FIG 223. — Albite Twinned about oo P So, oio Composition face the same Albite law Compare Fzg. 222
ooi in all the plagioclascs is greater and less than 90°, it must follow that the surface of then basal cleavages is not a plane, but that it consists of parallel strips of surfaces parallel to oio, and inclined to one another at angles alternately greater and less than 180°. Therefore basal cleavages
Descriptive Mineralogy
of the plagioclases very frequently exhibit parallel stnaUons when exam-
ined in light reflected at the proper angles (Fig 224) It is this Ivunnmg which, repeated in submicioscopic lamelltie, is believed to pro- duce the monoclmic pseudo- syrnmctiy of orthoclase It will be noted that the twinning plane has the position of the plane of
FIG 224 - StnaUons on Cleavage Piece hymmdiy in monodmiC of Ohgoclase (About natural bi/c ) crystals, and, consequently,
twins about this plane have
the same symmetry with reference to one anothci as amespomhng contiguous layers of mono- clmic crystals
In the pencline law the twinned portions are super- posed The individuals are twinned about b as the twin- nmg axis, and are united about
a plane nearly perpendicular
to oo P 06 (oio), known as the
Fio 225— Albile Twins with the Crystal the Twinning Axis and llu- Khomlm Sci- the Compos, turn F;uc The form r is
/l °° (4°3) Aniline law 8 °
"rhombic section" (Fig 225) The position of this section vanes with the different plagioclases, but is always nearly perpendicular to oio
Fio 226
Flti. 2*7
Fio 226 —Position of " Rhombic Sections " m Albitc (*1) an<l Amwthitc FIG 227 — Diagram of Crystal of Tnchnic Fciclbpar Kxhibilin Stnations Due to Polysynthetic Twinning According to the Albile and the Pcridmc Laws
(Fig 226). As nearly all pencline twins arc elongated in the direction of the ft axis, and the twinning is repeated, lamellae arc produced,
Anhydrous Trimetasilicates 421
which, in sections perpendicular to oio, cross the albite lamellae at angles near 90° (Fig 227) It is the presence of the two kinds of twinning in microclme that gives it its peculiar grating structure m polarized light (see Fig 219)
The plagioclases are light-colored, but pinkish and greenish shades are less common in them than in the potash feldspars Their streak is colorless They are usually translucent but in some cases are trans- parent Albite often exhibits a pearly luster and often a bluish shimmer Oligoclase when containing as little inclusions plates of hematite, glistens with a red shimmer and affords the finest sunstones The most bril- liantly colored plagioclases are some forms of labradonte, which, on cleavage surfaces, show a great display of yellow, green, red, purple and blue flashes m reflected light The cause of the play of colors is not known, but it is probably due to the presence of numerous very tuny parallel acicular inclusions
The refractive indices of the plagioclases vary with their compositions. For yellow light the \alues for the specified mixtures are as follows
58os
Before the blowpipe all the plagioclases fuse to a white or colorless glass, at the same time colonng the flame an intense yellow (albite), or a yellowish red (anorthite) Albite fuses at a lower temperature than anorthite The temperatures at which synthetically prepared plagio- clases melt completely are as follows
Albite (Abl0oAn0) i 5290 i 5333
Oligoclase (Ab?sAn22) i 5389 i 5431
Andesme (Ab&oAn4o) i 549 i 553
Labradonte (AbisAn,) i 5545 i 5589
Bytowmte (AbaoAngo) i 5691 i 5760
Anorthite (AbgAnoi) i 5752 i 5833
Anorthite i>55o°
1,521 AbsAni 1,362
i,49° Ab4Ani 1,334
1,450 AbsAni, 1,265
Albite 1,100° est
Albite is unattacked by HCi, but anorthite is decomposed by this reagent with the separation of gelatinous or pulverulent silica The intermediate plagioclases are more or less easily decomposed as they contain more or less of the anorthite molecule
The plagioclases are distinguished from the feldspars possessing the
422 Descriptive Mineralogy
monochmc habit by the twinning stnations on their basal cleavages, and from the potash feldspars of both monochmc and triclimc habits by the color imparted to the blowpipe flame The characteristics of the plagioclases best distinguishing them from one another are their specific gravities and their optical properties
The plagioclases weather to kaolin and mica (paragonilc) mixed with quartz and calcite in the more basic varieties, and to zeolites (see p 45) In rock masses the more basic varieties alter to epidote, m some instances into scapohte (p 423), and very commonly into the mix- ture known as saussunte, which is an aggregate containing /oisite or garnet as its most important component
Syntheses —Crystals of plagioclase have been nude by processes analogous to those employed in making oithoclase crystals For exam- ple, albite crystals have been produced by fusing SiOy and Al20;j with sodium wolframate, and by heating precipitated aluminium silicate with a solution of sodium silicate m a platinum tube to 500° Anorthite crystals have been made by long heating of a mixture of SiOj, AbQs and CaCOs m the proper proportions, and by fusing vcsuvianilc and garnet
Occurrence — Albite occurs m vein masses in certain crystalline schists but is much less common as a primary rock constituent than the other plagioclases It is, however, frequently found as a secondary product resulting from the changes produced m other plagiochuses by mclamor- phic processes, thus it is common in many crystalline schists Oligo- clase and andesme occur m granites and the other more siliceous igneous rocks and Ubradorite, by-
/ towmte and anorthite m the more basic rocks
Anorthite has also been found m meteorites
Localities — The localities at which crystals of the plagioclases are found are too numerous to be mentioned here Especially line crystals of albite occur at Roc-Tourn6 in the French Alps, m DaupmnS, France, at Amelia Court House, Va , FIG 2 28 —Potash- at Middletown, Conn, and at Chesterfield m Oiigoclase Crystal Massachusetts Excellent crystals of oligoclase Forms u m and c occur at Arendal and at other places in Norway, and
?R ?3oV(y) at McComb and Fme> m St Lawrence Co., N. Y.
Potash-ohgoclase occurs m certain igneous rocks at
Tyveholmen and elsewhere in Norway and in the lava of Kihmamljaro,
Africa. Its habit is prismatic (Fig 228) Crystals of andesme are
found at Bodenmais, m Bavaria, Arcuentu, in Sardinia, and at Sanford,
Anhydrous Trimetasilicates 423
in Maine Labradonte crystals occur at Visegrad, Hungary, and at Mt Aetna, Italy, and beautiful cleavage pieces come from Labrador, where it forms one of the constituents of a coarse-grained igneous rock Anorthite crystals occur at Volpersdorf, in Silesia, in the Aranya Mt, Siebenburgen, Hungary, at Pesmeda, Tyrol, in the inclusions in the lavas at Vesuvius, Italy, m the lava on the Island of Unjake, Japan, and at Phippsburg, in Maine.
Uses — Albite from the pegmatite veins of southeastern Pennsylvania and northeastern Maryland is mined for use in pottery manufacture
SCAPOLITE GROUP (Na4Al2(AlCl)(Si308)a-HCd4Aifi(A10)(Si04),)
The scapohtes comprise a series of isomorphous compounds of which the two end members are manaltte, Na4Al2(AlCl)(Si30s),j and mewnite> Ca4Alf,(A10)(Si04)(), Between these two are many intermediate com- pounds known under the collective name miz&omte Their composition is represented in terms of the manahte and meionite molecules, thus,
The theoretical compositions of the two end members of the series and of several intermediate members, and the actual compositions of four specimens of natural crystals are given below
Si02
AlaOs CaO
Na2O
Total
Theoretical, Ma .
Theoretical, MasMe
Ioo
Theoretical, MagMe .
Theoretical, MaMe
Si 9°
Is
Ioo
Theoretical, MaMe2.
Ioo
Theoretical, MaMes
Ioo
Theoretical, Me
25*
i?
Ioo
oo
Si02 AlaOs
CaO
Na20
K20
H20 Cl
Total
I 61 40 19 63
4 xo
?
?
Ii 54 86 22 45
Ioo
Iii 49 40 30 02
3 "
Ioo
Iv 41 80 30 40
19 oo
2 Si
3 i?
I. Manahte, Piaiwra, Italy
II Ripomte, Ripon, Quebec Contains ako 80% SOg, 49 Fe/>3 and a trace of MgO
III Werncntc, Rossie, N Y Contains also 10% 80s and 32 FeO.
IV Meionite, Mt, Vesuvius Contains also 46 MgO and 46% undecomposed
material
*Volatile
Descriptive Mineralogy
All the members crystallize in the pyramidal hemihedral division of the tetragonal system (tetragonal bipyramiclal class) in fairly simple columnar crystals with an axial ratio i . 442 for manahte and i 4393 for meionite The principal forms are oP(ooi), oo P oo (ioo), oo P(T 10),
oop2(2io), P(III), Poo (101) and
in A ill =43° 45' The habit of the crystals is always tolumnai , with oopoo(ioo) predominating in the prismatic zone, and also ooP(no)
prominent The Litter form predominates only m miz/on- ites The scapolites occur also in crystal grams embedded in limestones, in columnar and fibrous aggregates and in struc- tureless masses
All the scupohtes have a glassy lustei, which approaches
pearly They aie transparent translucent, colorless or
or
FIG 229 — Scapohtc Crystals with °oP, 1 10 (w), oo Poo, ioo (a), P, ii (r), and
311 (s) white, giay, greenish, bluish or
reddish and have a white streak Their cleavage is nearly perfect paiallcl to oo poo (roo) and imperfect parallel to ooP(no) Then fracture is uneven 01 con- choidal They are brittle, have a hardness of 5- 6 and density of 2 54 fpr manahte and 2 76 for meiomte, The refractive indices naturally vary with the proportions of the two molecules present. For the two end members of the group the indices for yellow light are marialite, 1.5463, 6=15395, meiomte, o>=r.5897,
€=15564-
Before the blowpipe all members swell and fuse to a white glass In hydrochloric acid, mixtures between Ma and MagMe arc insoluble, those between Ma2Me and MaMe2 are partially soluble and those between MaMe2 and Me are nearly completely soluble.
All members of the senes are distinguished by their crystallization and cleavage and all except pure meionite are characterised by the chlorine reaction They are distinguished readily from the feldspars by their fusibility with swelling,
Manahte and meionite are rare The common scapolites are the mizzonites of which dipyr and wernerite are the nontrunspurent vari- eties The former includes varieties occurring in elongated prisms con- taining between 54 per cent and 57 per cent SiOs, i.c., MaaMe to MagMe,
Anhydrous Trimetasilicates 425
and the latter embraces varieties containing between 54 per cent and 46 per cent SiCfe, or Ma2Me to MaMea
Occurrence — The scapohtes occur in crystalline schists, crystalline limestones and also m limestones included m volcanic lavas (meiomte), and on the contacts of igneous masses (wernente) They are found also m igneous rocks as the result of alteration of the feldspars, especially when these rocks are intrusive m limestones, and also as an alteration product of garnets In a few places they are associated with magnetite and apatite in veins of iron ores In most cases they appear to have been derived from feldspars by the action of metamorphic processes On the other hand, scapohte changes to albite, epidote, bio tit e, musco- vite and to a mixture of minerals
Localities — Meiomte crystals occur in the fragments enclosed in the lavas of the Lake Laach region, Prussia, and of Monte Somma, the precursor of Vesuvius, Italy Mizzonite is associated with meiomte at Monte Somma Dipyr occurs m clayey limestones m the Pyr- ennees, wernente at Arendal and Bamle, Norway, at Malsjo, m Sweden, at Diana, Lewis Co , and at Gouverneur and Pierrepont, St Lawrence Co , N Y , at Canaan, Conn , at Bolton, Mass , and manahte at Ripon, Quebec, and at Pianura, near Naples, Italy
Chapter Xix
THE SILICATES— Continued
The Anhydrous Polysilicates
UNDER the polysihcales are grouped all the minerals that cannot easily be assigned to the orthosilicates, the metasihcates or the tri- metasilicates They are usually very complex in composition and are commonly regarded as isomorphous mixtures or solid solutions of silicate molecules of various types*
The Brittle Micas
The brittle micas are so called because, while they possess a very marked cleavage which rivals that of the true micas in its pcifection, their cleavage foliae are brittle, and not elastic as arc the mica fohae
The group consists of four minerals of which throe are apparently mixtures of the molecules H2CaMg4(SiOi)s and HaCaMgAiO, and the fourth is approximately H2(Fe MgJAbSiO? The three are known as xantkopkylhte, brandtstte and chntomte and the fourth as ddoritoid Of these the last two are the most important Chloritoid is believed to be a basic orthosilicate, but, because of the similarity of its properties to those of the brittle micas, it is thought best to discuss it in the same group with them
All members of the group crystallize in the monocimic system with an hexagonal habit.
Clintomte (H0(Mg-Ca
Clmtomte, or seybertite, may be regarded as a mktuie of the mole- cules H2CaMg4(Si04)3 and HaCaMgAleOia in the proportion 4 : 5, which requires the percentage composition shown in line I below. The analysis of a specimen of the mineral from Orange Co., N. Y., is given in line II
Si02 A1203 FeaOs FeO MgO CaO H20 F Total
11909 4097 2228 13.36 430 100.00
II 19 19 39 73 61 i 88 21 09 13 n 4,85 1,26 101.72
Anhydrous Polysilicates 427
Well developed crystals are so rare that their axial ratio has not been satisfactorily established The best crystals appear as long, thick, six- sided plates with a well developed basal plane and several pyramids and domes with rounded edges If the axial ratio is assumed to be the same as that for biotite the principal forms are oP(ooi), -f P ob (027), £P (056), fP & (052), -iP(ii4), -?P(337), and -2P(22i) Many rA the crystals are superposed twins, like those of muscovite (Fig 230)
The mineral is reddish or brown, and
transparent or translucent It has a glassy
luster and a white streak Pressure and FIG 230 -Clmtomte Twinned
r t j j , , According to the Mica Law
percussion figures are easily produced on the Formg m
cleavage plates, and in nature parting often 337 and ;P , 012 (u) takes place along these directions, yielding
fragments with rectangular edges The hardness of clintomte is 4-5 and its density 3 i Its refractive indices for yellow light are i 646, 0=1657, 7=1658
Before the blowpipe clintomte becomes white and opaque but does not fuse In the closed tube it gives off water It is completely decom- posed by hydrochloric acid
It is distinguished from most other minerals by its micaceous cleav- age, and from the true micas by its brittleness and solubility in hydro- chloric acid
Clintomte occurs in a coarse, serpentimzed limestone at Amity, Orange Co, N Y
Chlontoid (H2(Fe-Mg)Al2Si07)
Chlontoid differs from the other brittle micas in being essentially a ferrous compound Its composition approaches the formula given above, though the analyses of many specimens depart widely from this.
Si02 AlsOs FeO MgO H20 Total
I 23 72 40 71 28 46 7 ii ioo oo
Ii 25 50 38 13 23 58 5 19 6 90 99.30
I Theoretical for HjFeAl2Si07 II Specimen from chlorite schists, St Marcel, Italy
The mineral is believed lo be monochmc m crystallization because of the similarity of its crystals to those of biotite It often occurs in six- sided plates, but more frequently m lenticular or spindle-shaped grams and sheaf-like and ball-like aggregates of plates and grains and in foliated masses Twins like those of biotite are also fairly common.
428 Descriptive Mineralogy
The mineral is dark green or black, and translucent It is strongly pleochroic in olive green, blue and yellowish green tints It has a glassy or pearly luster on its cleavage faces and a waxy luster on frac- ture surfaces Its hardness is 6-7 and density 3 4-3 6 Its refracti\e index is i 741
Before the blowpipe chloritoid exfoliates on the edges and fuses with difficulty to a black magnetic mass In the closed tube it gi\ cs off water It is unattacked by hydrochloric acid, but when in Jmc powder is com- pletely decomposed by sulphuric acid Some forms of ott relit e are sol- uble m strong nitric and hydrochloric acids, with the separation of gelatinous silica
Masonite is a dark grayish variety from Nalick, R I
Qttreltte contains a little manganese and has a slightly chfTcicnt formula from chloritoid Its composition may be best represented by Ha(Fe MnjAJaSfcOo Itssp gr=33
The chlontoids appear to be fairly stable, as their only alteration products thus far noted are the chlorites and the micas and otti elite
Occurrence —All varieties of chloritoid are found principally m fine- grained schists where they are believed to be the result of regional and contact metamorphism
Localities —The most noted occurrences of chloritoid are Pregattun, Tyrol, St Marcel, Italy, Ottrez, Belgium; Natick, R, I , and Augusta and Patnck Counties, Va,
Chlorite Group
The chlorite group is so named because its principal members are green. The group comprises a number of platy hyduws magnesium, aluminium silicates that appear to be isomorphous mixtures of mole- cules that are approximately BLi(Mg FeAlgSiOu and H,| (Mg- FcXiSisOu, the former of which is known as the amesite molecule (designated At), and the latter as the serpentine molecule (indicated by Sp). The ser- pentine molecule is represented in the platy form of serpentine known us anhgonte, which may be regarded as one of the end members of the series The independent e\istence of the arnesite molct ult1 is doubtful The mixture of these two molecules gives rise to the orthot ///orz/rs, which constitute the principal of the two subgroups of the chlorites. The other subgroup is known as the group of the leptocUmfa These con- sist of one or both of the two molecules mentioned above and others that may be regarded as derived from them Their composition is too com- plex to be represented by any simple formula
Anhydrous Polysilicates 429
Orthochlor1Tes
The orthochlontes comprise the minerals
Si02 AI203 FeO MgO H20
Coru'ndophhleSpA.U-Sp3A.t7 SpAU =26 i 29 3 31 8 12 8
Prochlonte Sp3At7~Sp2At3 SpAt2 =25 5 21 6 26 6 14 9 n 4
Chnochlore Sp2Ata-SpAt Sp2Ats=3o 03 22 o 34 8 12 9
Pennimte SpAt -SpaAt2 SpsAt2=34 7 14 6 37 7 13 o
Analyses of typical specimens are as follows
Si02 A12O3 Fe2O* FeO MgO CaO H20 Total I Corundophihte 24 77 25 52 15 19 21 88 n 98 99 34
II Prochlonte 26 02 20 16 i 07 28 08 15 50 44 9 65 100 92
III Chnochlore 29 87 14 48 5 52 i 93 33 06 13 60 100 19*
IV Pennimte 33 71 12 SS 2 74 3 4° 34 7° 66 12 27 100 03
I Chester, Mass
II Zillerthal, Tyrol
III West Chester, Pa
IV Zermatt, Switzerland
Contains also NiO= 17, Cr2O3=r 56.
The orthochlontes crystallize in tabular and pyramidal crystals that are usually repeated twins so that their true nature is difficult to decipher The simpler crystals have a monoclmic habit, but the twins are usually hexagonal or rhombohedral in habit Then crystallization is believed to be monoclmic, with the axial ratio 5774 .1:2 2772 and £=89° 40', The most common forms appearing on them are oP(oor); Pob(oii), ?P(22S), ]P(Ti2), JP&(043), -AP (40.11), oop6b(iOI) and — 6P(26i) (Fig 231) Twins are very common The two most com- mon twinning laws are the mica and the pennme laws In the former the twinning plane is perpendicular to oP(ooi) and in the zone with oP(ooi) and — aP(ii2) (Fig 232, compare Fig 193) The two parts are levolved 60° with respect to one another In the pennine law oP(ooi) is the twinning plane and the composition face (Fig 233) Twins following the first law have their twinned parts either side by side (Fig 234), or superposed (Fig. 232 Those following the pennine law have their parts superposed The twinning is often repeated so that complicated trillings and sixhngs are produced
Chnochlore crystals are tabular with hexagonal outlines but a mono- clime habit (Fig 231), and penmmte is in thick tabular crystals with a
Descriptive Mineralogy
trigonal outline and a rhombohedral habit, or in slender prismatic ones resembling steep rhombohedrons (Fig 235) Its characteristic twins are according to the penmne law (Fig 236) Prochlonte and corun- dophilite are found in six-sided plates without well developed crystal forms.
Fig 231 Fig 232 Fig 233
FIG. 231 —Clmochlore Crystal with oP, ooi (c), °°Pcb, oio 4P3, 401 (f),
and -Ps, 132 W
FIG 232 — Clmochlore Twinned According to Mica Law, in which the Twinning
Plane is Perpendicular to oP(ooi) and in the Zone with oP(ooi) and -lP(ii2)
FIG. 233 — Clmochlore with Same Forms as in Fig 232 Twinned about oP(ooi) as
Twinning and Composition Face, Pennine law.
Fig 234
Fig 235
Fig 236.
234 — Clmochlore Twinned According to Mica Law, but with Individuals Side by Side with oP(ooi) common and Irregular Compoulion Faces* (225) and y- 55 (205)
235 — Pennmite Crystal with oP, ooi (c) and a Form Resembling 3!*, 3031 (w). FIG 236 — Pennmite Crystal Twinned about oP(ooi), Pennine Law
The orthochlorites have a glassy luster with a slightly pearly luster on the basal plane. They are usually some shade of green, blackish and bluish green being the most common shades. At a few localities white or yellow varieties are found. Varieties containing chromium are often
Anhydrous Polysilicates 431
rose-colored or violet The streak of all varieties is white or light green All are strongly pleochroic in shades of green m gieen vari- eties, yellow and brown in brown varieties, and violet and carmine in rose varieties Their cleavage is distinct parallel to the base (ooi), yielding lamellae that are flexible and slightly elastic Percussion and pressure figures, with rays in the same relative positions as m the micas, occur naturally and often a parting takes place along their planes yielding triangular plates The hardness of all orthochlontes is below 3 and their density is 2.5-3. For the different varieties these properties are.
H Sp Gr
Prochlonte 1-2 2 78-2 96
Clmochlore 2-2 5 2 65-2 78
Pennmite 2-2 5 2 6 -2 85
Corundophihte 25 29
The refractive indices for yellow light are* in penmmte, 575, in chnochlore, a— i 585, 0=i 585, 7=1.596, m prochlonte, #=i 58+ and in corundophihte, £=1 583
Before the blowpipe the orthochlontes exfoliate and fuse with diffi- culty. Some varieties whiten The varieties rich in iron fuse more readily than those m which there is little iron — in some instances to a black glass In the closed tube all yield water when strongly heated Hydrochloric acid attacks all varieties with difficulty — after fusion with more ease Sulphunc acid completely decomposes them
Synthesis — Chlontes have been produced artificially by the action of alkaline solutions on pyroxenes.
Occurrences — The orthochlontes are alteration products of various silicates They occur as essential constituents m crystalline schists (chlorite schists), and as the alteration products of silicates in igneous rocks, in which case the latter assume a green color The orthochlontes also form pseudomorphs after garnet, biotite, augite, hornblende, etc , and sometimes they occur filling little veins cutting through altered rocks Corundophihte is frequently associated with the mineral corundum
Localities — The localities at which the orthochlorites occur are so numerous that even all of the most important cannot be mentioned here. In the United States corundophihte occurs at Chester, Mass., and Asheville, N C , pyrochlorite at Foundryrun, Georgetown, D C , and at Batesville, Va , pennmite at Magnet Co/c, Arkansas, and chnochlore at West Chester, Penn
432 Debcbipt1\E Mineralogy
Leptochlorites
The nameleptochlonte is usually given to the chlontes that occur in fine scales and fibers They are very complex in composition Because they do not occur ui distinct crystals the.r crystallization ,s not ceitamly
e leptochlorites are hke the orthochlontes in general appearance, and in origin They are, however, completely soluble m hydrochloric acid with the separation of gelatinous silica
Of this group thuringite and ddesvte are the best known The former 1S in very fine dark green and pleochroic scales It fuses to a black mag- netic bead It forms pseudomorphs after garnet at the Spurr Mt iron mine at Spurr, Mich Delessite is usually green, but w in lare cases nmk' It usually occurs in bundles of fibers that are strongly pleochro.c The green varieties, viewed across the fibers are dark peon Viewed along their axes they are yellow This chlorite is a common alteration product of pyroxene and amphiboles, and it frequently occuih as he filling of amygdules in basic volcanic rocks The minoul when heated becomes brown or black and finally fuses with dfficulty to a black mag-
neticbead . „ . . .,
Analyses of typical specimens of the two minerals are given m the
following table
Si02 Ai203Fe203 FeO CaO MgO H20 Total Thunngite, Spurr,
Delessite, Dum-
barton, Scot-
land , 32 oo 17 33 i 19 "-4S I 57 20.4 IS 45 4i
Vesuvianite
Vesuvianite is a common metamorphic mineral in limestones. It is extremely complex m composition, apparently consisting of isomorphous mixtures of the two compounds CaAlaAl(OII'F)(Si04)5 and Ca2Al(OH)Si207 Its composition may perhaps be better rep- resented by the general formula R'4Al2Ca7Sio024, in which R/4 may be Ca2,(A10H)2, (A102H)4 or H4 Four analyses, which emphasis the great variations m composition shown by crystals from different localities are quoted below*
Anhydrous Polysilicates
Si02
AbOs
Fea03 FeO
CaO
MgO
MnO
K20
Iq 30
5°
NaaO F H20 at 100° H20+
Less 0=F Total
Iii 44
Is
Ioo 21
I Garnet colored masses and crystals form Pajsberg, Sweden II Finely crystallized material from Italian Mt , Gunnison Co , Colo
III From Franklin Furnace, New Jersey Contains also ZnO=i 74,
i 48, and a trace of PbO
IV Cahformte Fresno Co , Cal Also 91 per cent CO.
CuO=
Vesuviamte occurs both massive and crystallized Its crystals are m the tetragonal system (ditetragonal bipyrarmdal class), with an axial ratio of about i 5375 This vanes with the composition and is, therefore, different m specimens from different lo- calities The crystals are usually thick columnar m habit, but some crystals are pyramidal and otheis acicular.
The columnar crystals usually 237suviamte Crystdlb Wlt IIO
(m]j oopoo,ioo (a), in (p) and oP, oox (c)
In
contain ooP(iro) and °oPoo
(100) m the prismatic zone,
and oP(ooi), P(in), and
often POO(IOI), 3P(33i), °oP2(2io), and 33(311) (F 237)
all about 60 forms have been observed on them The angle
5o° 39'
The mineral is glassy in luster and yellowish, greenish or brownish, rarely blue or pmk It is transparent or translucent. A bright green, or gray and green, translucent, massive variety from points in California is used as a gem under the name cah/ornite. The streak of all varieties is white The cleavage of the mineral is indistinct parallel to oo P(no) and oo Poo (100) and its fracture conchoidal. Its hardness is 6-7 and density 3 35-3.45. Its refractive indices foi yellow light are 1.705, i 701
434 Descriptive Mineralogy
Before the blowpipe vesuviamte melts to a swollen brown 01 green glass It is decomposed with difficulty by cicids, but after being strongly heated it dissolves with the separation of gelatinous silica The min- eral powder reacts alkaline
The mineral is characterized by its form when in crystals and by its easy fusibility
The recognized varieties that are used as gems are
Cdtformte, a white, green or gray and green variety in finely gran- masses, resembling jade
Cypnne, a blue variety containing copper
Its principal alteration products are mica, chlorite and steatite, and other minerals are also known to be foimed from it by weathering
Occurrence —Vesuviamte is preeminently a contact mineral It occurs in limestone metamorphosed by granite and othei igneous rocks, and also in crystalline schists It is found also as well developed crys- tals on the walls of veins containing quart/, calcitc, gurnet and ore minerals
Localities — Good crystals are common at a number of places where limestones are in contact with igneous rocks, notably at Piitsch, and in the Monzom Mts , m Tyrol, at Zermatt and at othei points m Switz- erland, at Vesuvius, in the Alathal, and the Albanian Mts,, m Italy, and at many places m Norway and Sweden In North America good crystals occur at Sandford, Phippsburg and other places in western Maine, near Amity, N Y , and at Templeton, Quebec, and a fine- grained, massive variety occurs in Inyo and Tulaie Counties, in Cali- fornia Californite is best known from Indian Cieck, Siskiyou Co , and from a point 35 miles east of Sclma, m Fresno Co , California Other ' localities are at Big Bar Station, Butte Co , and , in Tulare Co., m the same State
Production —The quantity of californite used as a gem stone in 1909 was about 3,000 Ib , valued at $18,000 In 1912, however, only $275 worth was used
Tourmaline (RoAl (B OH* F) a R=H, Al, Mg, Fe, Al, Cr, Fe, K, Na
Tourmaline is of great scientific interest because of its complex crys- tallization, its handsome crystals and the phywcal properties which it exhibits so beautifully. Moreover, it furnishes gems of many colors, which, because of their brilliancy, are greatly admired by many persons The mineral appears to be a derivative of the alumino-borosilicic acid
Anhydrous Polysilicates 435
in which the hydrogen may be replaced by Al, by Cr, by Mg and Fe" or by Li or Na, giving rise to four groups of com- pounds between which are many gradations Moreover, in most speci- mens a portion of the hydroxyl is replaced by fluorine In other words, the mineral is an isomorphous mixture of several substances that are derivatives of the alummo-borosihcic acid mentioned The four groups of tourmalines that are clearly distinguishable are
1 Alkah tourmalines, which are colorless, red or green, and trans- parent
2 Iron tourmalines, which are usually dark blue or black and trans- lucent
3 Magnesium tourmalines, which are yellowish brown, or brownish and translucent
4 Chrome tourmalines, which are dark green, black and translucent, or colorless and transparent
Typical analyses of these four varieties follow
I Ii Iii Iv
SiO2 38 07 34 99 37 39 56
9 99 9 63 Io 73 8 90
42 24 33 96 27 89 32 58
FeO 26 14 23 64
MnO 35 .06
CaO 56 15
MgO 07 i 01
NaaO 2 18 2 or
&20 44 34
LiaO i 59 tr
HfeO 4 26 3 62
F 28
Ti02
Total . 100 29 100 oo 100 42 99 70
I Rose-colored (rubellite), from Rumford, Maine II Black, from Auburn, Maine
III Brown, from Gouverneur, N Y. The A1A includes ,10 of Fe208.
IV Green, from Etchison, Montgomery Co , Md Contains also 79 FcjOj, 05
NiO and
The varieties recognized by distinct names are (i) ordinary, black and brown, (2) rubellite, pink or red, (3) indicolite, blue or bluish black, (4)
Descriptive Mineralogy
Brazilian sapphire, blue and transparent, (5) Brazilian cm&ald, or Brazilian chrysolite, green and transparent, (6) peridot of Ceylon, honey- yellow and transparent and (7) acfaoite, colorless and transparent
Tourmaline forms handsome crystals that are frequently character- ized by possessing a triangular cioss-section They ciystalh/c in the rhombohedral division of the hexagonal system and aie hemimorphic (ditrigonal pyramidal class), with an axial ratio of i 4474 The crys- tals are usually prismatic or columnar in habit, and ore teimmated by
Fig 238
Fig 239
00 ?
FIG 238 — Tourmaline Crystals with H — -, loTo
Fig 240
Co P
1120 (a), and H — u, ion (r). --- it, 0221 (o) and oP, ooi (0 at analogue polo,
and H — /, oiu(ri) and -- /, 01X2 (r) at dnliloguu pole
FIG 239 — Tourmaline Crystal with a, m, m\, c, o, r, ami us in Fig 28 Also
3P| _j.i — *ut 2131 (/) 6 ib at (inuloguc polo
FIG 240 — Cooling Crystal of Tourmaline Powdered with .1 Mixture of Minium and Sulphur to Show the Distribution of the IfileUnt Charge, The upper end is the analogue pole
rhombohedrons The most prominent prismatic fdccH arc ooP(ioTo), oo f 2(1120) and the most common terminal faces R(ioi i), — R(oi f2), -2R(o22i)3 Ra(2i3i), R6(325i) and -11(1232), though many other rhombohedrons and scalenohedrons have been observed. Most forms are hemimorphs so that the opposite ends of the c u-\is are differently terminated (Figs 238 and 239) The prismatic faces are vertically striated and the mterfacial edges are often rounded, The angle icTi
The mineral has a vitreous luster whether transparent or opaque. It
Anhydrous Polysilicates 4J7
is brittle and has no distinct cleavage Its fracture is conchoidal Its hardness is 7-7 5 and its density 3 007-3 I34 f°r alkah varieties, 3 036-3 104 for magnesian varieties, 3 140-3 212 for blue iron varieties and 3 122-3 220 for green and black varieties The color varies more than in any other mineral, the same crystals often exhibiting different colors at opposite terminations Moreover, many crystals show a zonal arrangement of colors, with concentric colorless, red and green layers The streak of all varieties is uncolored The mineral becomes elec- trified by friction and like other hemimorphic substances is pyroelectric The analogue pole is usually more simply terminated than the antilogue pole, in many instances showing only R(IOII) (Fig 240) The refrac- tive indices for yellow light in colorless crystals are i 6422, i 6225 In iron-bearing varieties the refraction is stronger
Dark varieties exhibit very strong pleochroism Viewed in the direc- tion of the c axis the mineral is always, except in the case of colorless varieties, darker than when viewed in a direction at right angles to it In very dark varieties the ray vibrating perpendicular to c is almost completely absorbed, while the ray vibrating parallel to c passes through with a dark brown or dark green tint Thus, thin slices cut parallel to the c axis will let through only light that vibrates m the plane parallel to c Tourmaline tongs are two such pieces or plates of dark tourmaline mounted so that they may be revolved in their own planes When the c axes in the two plates are parallel light is transmitted This light is said to be polarized because it all vibrates in a single plane When the c axes are crossed the light that passes through the first plate is entirely absorbed by the second, so that no light passes through
The behavior of tourmaline before the blowpipe varies widely Alkaline varieties are practically infusible Iron varieties fuse with great difficulty and magnesium varieties very easily to a blebby glass
When fused with a mixture of acid potassium sulphate and pow- dered fluorspar all varieties give a distinct reaction for boric acid
Tourmaline is readily distinguished from all other minerals by its crystallization, hardness, lack of cleavage and the reaction for boron In massive forms it differs from garnet and vesuwamte which it some- what resembles by its difficult fusibility and bnttleness. The imneral is, on the whole, very stable It is known, however, to alter into mica, chlorite and steatite
Synthesis — The mineral has not been produced artificially
Occurrence — Tourmaline is a characteristic pneumatohtic product It occurs in pegmatites, in quartz and ore veins, and in limestones and schists on the peripheries of granite masses where it is the result of
438 Descriptive Mineralogy
contact action It occurs also as an original, pyrogemc mineral in acid igneous rocks The variety in limestone is usually brown The lithium varieties are usually associated with lepidohtc
Uses,— The transparent varieties are used principally as gem stones, and the darker, translucent varieties in optical instruments
Localities — Tourmaline is so common that an enumeration of its occurrence is impossible in the present place. Red or gieen transparent varieties occur at Ekaterinburg, Uial, on the Isle of Elba, at Cam- polonga, Switzerland, Pemg, Saxony, and in Mmas Geraes, Brazil In the United States fine brown crystals occur in the limestone at Gouver- neur, N. Y , and handsome black ones at Pierrepont, N Y , New Hope, Penn , and in Alexander Co ,N C The gem tourmaline oum sat several points in western and central Maine, at Hadclum, Conn , and in San Diego Co , in California. The Maine localities uie at Hebron, Pans, Poland and Auburn The tourmalines are in pockets m pegmatite The green varieties are most common, but all colors occur, and many crystals are variegated The centers of the gem industry m California are P#la and Mesa Grande, San Diego Co , where many pink tourma- lines and a few green crystals occur associated \uth the lithium mica, lepidolite, in pockets in a pegmatite dike The best of these when cut bring $20 per carat
Production — The total output of #cm tourmaline in the United States during 1909 was 5,110 pounds valued at $133,192, but in 1912 the yield had fallen to $28,200,
Cordierite (OM*'Pe)2AIa(A10)aaUOui)
Cordierite, dichroite, oriohte, may be an isomotphous mixture of several molecules Its composition is apparently as shown by the formula given above, although the persistent appearance of water in all recent analyses may indicate the presence of hydroxyl in the molecule Since, however, the mineral readily undergoes weathering, most authors regard the water as due to some hydrous alteration product , I f the water is regarded as essential the formula becomes Ha(Mg- FiOiAlsSiioOa? The calculated composition of the mineral and the actual compositions of some specimens, as shown by analyses, are:
Si02 AbOa Fe20'i FeO MnO MO H0 Total
Theoretical 51 36 34 96 ,, . . , 13 68 . JQO oo
Haddam, Conn 49 14 32 84 63 5 04 19 10 40 1,84 xoo 08
CabodeGata 4858 3244 315 917 tr. 6,63 . . 99.97
Anhydrous Polysilicates
Cordiente is orthorhombic (bipyramidal class), with the axial ratio .5871 i 5584 Its crystals are usually short columnar with an hex- agonal habit due to the equal prominence of oo P(no) and oo P co (oio) (Fig 241) In addition to these planes, there are usually present also oP(ooi), P 06 (on) and £P(ii2) The angle no A ilo=6o° 50' Inter- penetration twins, with ooP(no) the twinning plane, are known but they are not common Contact repeated tu ins, twinned parallel to the same plane, are more common They usually possess a pseudohex- agonal habit The cleavage is good parallel to oo P 60 (oio) and there is often a parting parallel to the base (ooi)
When in fresh condition the mineral has a glassy luster and a bluish, yellowish or grayish tinge by reflected light. It is transparent or translucent and colored varieties are strongly FlG 24* — Cordicntc Crys tnchroic in dark blue, green and grayish tal with cop iIO (w),
11 T.J T.T.L 00 P£C, Oil (fl), 00 POO,
yellow shades, which become more intense OIO m 130 (d) upon heating Its hardness is 7-7 5 and sp oP? OOI'(c)j in (r)| gr 2 63 Its refractive indices vary with the composition In specimens from Ceylon, ai 5918, /3=i 5970, 7=1 5992
Before the blowpipe cordiente is difficultly fusible It is very slightly attacked by acids, but is completely decomposed when fused with alka- line carbonates
The mineral is distinguished from quartz most easily by its cleavage and crystallization
Cordiente weathers readily into fibrous or scaly aggregates of micaceous minerals yielding well defined pseudomoiphs. The end product of the alteration is a muscovitc, or a mixture of this mineral and biotite Several of the alteration products are so characteristic that they have icceived distinct names Among these are chlorophylhte, a green chlontic mineral, fahlumte, a serpentine-like mass, gigantohtc, a brown, gray or green micaceous aggregate m large 1 2-sided prisms made up of thick plates, and p%mtet a dark green aggregate forming prisms that are platy parallel to the base
Syntkess — Crystals of cordierite have been produced by fusing its constituents in. an open crucible and then cooling the mass very slowly, but since the result was an anhydrous product its identity with cordiente is doubtful
Occurrence —Cordiente occurs ab crystals embedded in gneiss,
iP, uaj, and 3? 3, 131 (0)
440 Descriptive Mineralogy
schists, granite, quartz porphyries, and rhyohtic and andesitic lavas It occurs both as a pyrogenetic mineral and ab a product of contact metamorphism
Uses — Cordiente is used to some extent as a gem
Localities — Good crystals of cordiente arc found in gneiss in Boden- mais, Bavaria, and at Arendal and other points in Norway, in the vol- canic bombs thrown out by the volcanoes of the Lake Laach district in Prussia, and the volcano Asama Yama, m Japan, and m the anclcsitc at Cabo de Gata, Almena, Spain It occurs also in gianitc veins at Had- dam and near Nonvich, m Connecticut, in gneiss, at Guilfoid, m the same State, at Bromfield, Mass , and near Richmond and Unity m New Hampshire.
Chapter Xx
THE SILICATES— Continued
The Hydrated Silicates
Chrysocolla (H2CuSiO4-H2O, or CuSiO* 2H2O)
CHRYSOCOLLA occurs usually in dense masses without any sign of crys- tallization, but at several places it has been found in spheruhtic forms that are made up of fibers that are apparently acicular crystals The symmetry of these, however, is unknown The general view is that the mineral is colloidal
The theoretical composition of chrysocolla, corresponding to the formula given above, and the analysis of a specimen from the Old Dominion Mine, in Arizona, are given below
SiOo CuO FeoOs AkOs Mn2Os EbO Total Theoretical 34 23 45 23 20 541 oo oo
Globe, Arhs 31 58 30 28 84 6 27 2 22 28 71 99 90
Many analyses show the presence of MgO, CaO and FeO, and some the presence of ZnO
The various analyses that have been recorded vary so widely, espe- cially in the determinations of water, that the true composition of the mineral is still m doubt It is possibly a solid solution of colloids
An analysis of a specimen from Huiqumtipa, Chile, which is thought to have been exceptionably pure gave
SiO2 A1203 CuO FeO CaO MgO H30 Total 46 14 58 28 85 i 38 i 64 83 20 15 99 57
This corresponds to the formula Hs(Cu OH) (8103)2 HfoO The spec- imen w<is a turquoise blue enamel, with a hardness of 3 5 and a sp gr 2532
Chrysocolla has an opal-like or earthy structure It is green or turquoise blue and translucent Its streak is greenish white. Impure varieties may be brown or black and have a dark brown or dark green
142 Descriptive Mineralogy
streak. It has a conchoidal fracture and is brittle Its hardness varies between 2 and 4 and its density between 2 and 2 2
The mineral is infusible before the blowpipe, but it colors the flame green It yields water in the closed tube and is decomposed by HC1 with the production of pulverulent silica
It is distinguished from other green and blue silicates by its reaction toward HC1 and the green flame it imparts to the blowpipe flame
Occunence— ChsocolU is produced by the oxida-tion of copper compounds and combination of these oxidation products with silicic acid in the upper portions ot ore veins It sometimes replaces other minerals, as atacamite, cerussite and labradontc and forms pseudo- morphs after them
Uses — Chrysocolia is mined with other ores of coppei and is treated with them for the metal it contains. Exact statistics of the quantity pro- duced are not obtainable
Localities —The mineral occurs in many copper mines, especially m Bohemia, Hungary, Italy and Russia It occurs as blue crusts on the basalts near Somervillct N J , as a bluish green matrix cementing black masses at the Old Dominion Copper Mine, Globe, Arix ; and intimately mtergrown with opal at the Boleo Mine, California It is also abundant m Chile, where it occurs in all varieties,
Glauconite [Hydrous Silicate of Iron and Potassium]
Glaucomte, or greensand, is an important constituent of some sedi- ments It is probably a mixture of several substances, of which the compound FeK.(SiOs)2 H20 may be most essential. Tt occurs as little round grains and pellets, mixed with the shells of foraminifera, forming beds o,f sand, and also as a component of limestone, marl, clay and sand- stone Glaucomtic sands, because of their richness in potash wcie formerly used as fertilizers m the regions in which they are found,
Analyses of glaucomte grams from Ashgrove, near Elgin, m Scot- land (I), and of glauconite sand from Antwerp, Belgium (II), are as follows*
Si02 A1203 Fe208 FeO MgO CaO Na20 KaO H0 Total
I 49 09 15 21 10,56 3 06 2 65 55 i 21 6 o<[ ii 64 100 02
Ii 50 42 4 79 19 90 5 96 2 28 3 21 ,21 7 87 5 28 99,9:2
Glaucomte is blackish, or yellowish green, in color, with a light green streak It resembles earthy chlorite, but is probably amorphous. Its hardness is 2 and its density 2 2-2 8. It is opaque*
Hydhated Silicates 443
The mineral fuses with difficulty to a black magnetic slag and is decomposed in part by strong hydrochloric acid, but aftei fusion is com- pletely dissolved the separation of gelatinous silica It yields water in the closed tube
Occunence and Localities — Glaucomte occurs in oceanic deposits and m sedimentary rocks of nearly all geological ages Its principal occurrences in this country are in the belt of cretaceous beds on the Atlantic coastal plain It is best known from the coastal portions of New Jersey and from Spotsylvama and Stafford Counties, in Virginia It apparently occurs also as a decomposition product of augite m certain basaltic rocks In all cases it appears to have been produced by sec- ondary processes, MZ , by the absorption of potassium compounds and soluble silica by colloidal ferric hydroxide In the ocean these com- pounds result from the action of decaying animal matter upon ferrugi- nous clays and fragments of potassic silicates in rocks, \vhen of later origin than the rocks themselves, by the action of solutions of potassic salts upon iron hydroxids
Greenalite differs from glaucomte in containing no potassium It may be a hydrated ferrous silicate (FeSiOs lEfeO) or a ferrous-ferric silicate (Fe2Fes (8104)3 sHaO) It occurs as round grains in the cherts of the Lake Superior region, and in its physical properties it closely resembles the glaucomte granules in rocks. It is believed to be the source of the hematite ores of the district.
Apophyllite (H7KCa4(Si03)s 4|H2O)
Apophyllite differs from the zeolites (p 445) m containing no alummia and m having some of its water replaced by fluorine, but m its general appearance and its manner of occurrence it is like them The calculated composition corresponding to the formula usually assigned to the mineral is given m I Analysis II is of a specimen from Bergen Hill, N. J , and III of a specimen from Golden, Colo Some specimens contain also small quantities of ammonia,
Si02 A1203 Fe203 CaO Na20 K20 H20 Fl Total
I S3 7 25 o 5 2 16 i 100 oo
Ii 52 24 25 03 4 05 16 61 2 21 100 14
III 51 Bg i 54 13 24 51 59 3 81 16 52 i 70 too 69
The mineral is tetragonal (ditetragonal bipyramidal class), with a : b : c- i . i 2464. Its crystals usually contain the forms oo P oo (100),
Descriptive Minkkalcxsy
P(III) and oP(ooi), and often ooPjfoio) 01 <x>P2(2io) Tn addition, about 55 other forms have been identified, but most of them die rare. Many of these are \icmal planes with large (uiameteis The crystals are of four types, (i) pyramidal with P(ITI) piodommating, (2) pris- matic with ooPoo(ioo) and P(III), the former predominating, (Fig 242A), (3) cubical, withooP (100) and oP(ooi) equally prominent (Fig 2426), and (4) tabular parallel to oP(ooi) (Fig 2420) Twinning par- allel to P(iii) is rare The angle in AiTi 76° The mineral also occurs in granular and lamellar masses
Apophylhte is glassy on fracture surfaces and most crystal faces, but on oP(ooi) it is distinctly pearly It is while, grayish, flesh-colored or red, and transparent Its streak is white It possesses a very peifect cleavage parallel to oP(ooi) and a less perfect one paialiel to oo P(no)
A B C
FIG 242 — Apophylbte Crystals with oo?co , TOO (a), P, TTT oP, 001 and 00 P3> 3*° (y) A Prisrrutu B Cubical C T.ibulu.
It is brittle Its hardness is 4 5-5 and its density "2-24. Tt is stiongly pyroelectric For yellow light, co= i 5356, i 5 $68.
Before the blowpipe apophylhte exfoliates and fuses easily to a blebby white enamel, and imparts a violet color to the flame nan the assay. In the closed tube it loses water and becomes opaque. It also loses water upon being pulverized Most specimens give the reaction for fluorine Half the water is lost at a comparatively low temperature (24o°-26o°), but the last remnant of the remainder is driven off only at a red heat At 400° fluorine begins to escape The mineral dissolves in HC1 with the separation of slimy silica. At i&>°- igo", umlei a pressure of 10-12 atmospheres, it dissolves in water, and from this solution it crystallizes upon cooling
Apophylhte is recognized by its crystallization, its pearly luster on the basal plane, and its fluorine reaction.
Syntheses —Apophylhte crystals have been obtained from solutions of its constituents in water containing COa, heated in a closed tube to 150-160° They have also been formed by the action of a solution of
Hydrated Silicates 445
potassium silicate on gypsum The mineral has also been described from the nuns of old Roman mason ly around hot springs
Occurrence — The mineral occurs in the cavities of volcanic rocks, in veins in granite and gneiss and m ore veins and ore deposits m lime- stone It is also found in the locks surrounding hot springs Under some conditions it alters to calcite, and to pectohte (p 369)
Localities — Good crystals of apophylhte occur at St Andreasberg and Radauthal, Harz, at Stnegau, Silesia, near Cipitbach, in the Seisser Alps, Tyrol, in the magnetite mines at Uto, Sweden, at Disko, Green- land, at many points in eastern Nova Scotia, at Bergen Hill, N, J.; at Table Mt., Golden, Colo., and at Santa Barbara, in Brazil
The Zeolites
The group known as the zeolites comprises minerals that are hydrous silicates of aluminium with calcium, sodium, potassium, barium or strontium The calcium compounds are commonest, followed by the sodium compounds Compounds with the other elements are com- paratively rare
While it is probable that some of them are primary products resulting from the cooling of a magma, in the great majority of cases the zeolites are secondary products derived by the alteiation and hydration of alkali-aluminium silicates, such as the fcldspais, Icucite, nephelme, etc They are nearly always found in veins, 01 on the walls of cie vices in rocks (especially \olcanic rocks), where they have been deposited by circulating water They are commonly associated with calcite, pecto- hte, datohte or prchnite All are well crystallized and some of them are m complicated crystals
Many of the zeolites have been recrystalhzed from solutions in superheated water The solutions having been produced by the action of various reagents upon aluminous silicates
Before the blowpipe all the zeolites fuse with intumescence, or bub- bling, and all give water in the closed tube. They are comparatively soft (3 5-5 5), and have a low specific gravity (2-2.4), The most com- mon zeolites are
Ptilohte (Ca-K2
Ileulandite HtCaAIaCSiOsV 3H20 Monoclmic
Philhpsite (Ca-K2)Al2(Si03)4 4i>H20 Monoclmic
Harmotome (H2(Ba K2)Al2(Si03)r sH20 Monoclmic
Stilbte (Ca-Na2)AkSioOi6 6H20 Monoclmic
Laumonfate CaAlSiO 4HaO Monoclmic
446 Descriptive Minkk Al< X J V
Scolecite Ca(AlOH)2(SiO<03 2lIjQ Monochnic
Natwhte Na2Al(A10)(SiOah 2H2O Oithorhombic
Thomsomte (Ca Na2)Al2(SiOi)2 2jH20 Oithorhombic
Chabazite (Ca NaaJAb (8103)4 -6H2O Hexagonal
Analcite NaAKSiOsV HbO Isometric
Ptilohte ((Ca K2-Na2)Al2SiioO24 5H2O) occuis in shoit, hanhke, white or colorless crystals, aggregated into delicate tufts or spongy masses Their system of crystallization is unknown Their luster is vitreous The needles apparently have a, cleavage pcipenchcular to their long a\es The mineral is scarcely acted upon by boiling hydio- chlonc acid
The composition of ptilolite from Colorado ib quoted as follows
Si02 AlaQs CaO NoaO KuO HaO Total
70 35 ii 90 3 87 77 2 83 10 18 09 90
Its refractive indices are about i 480
The mineral is found m the cavities of a volcanic lock in Giccn and Table Mts , Jefferson Co , Colo
Heulandite (H4CaAl2(SiOa)0 3HL>0)
Heulandite occurs m monochmc crystals (monoclmic pusmatic class), with the axial ratio 4035 . i . 4293 and /S<)i° 25', in foliated and granular masses and in globular aggregates
The theoretical composition of heulandite (the fowwhi of \vith may also be written CaAlaSioOio- SHO), and the analysis of a specimen fiom Anthracite Creek, Gunmson Co , Colo , are given below*
Si02 Al20<j CaO NaaO K20 HaO Total
I 59 22 16 79 9 20 14 7(> roo oo
Ii 57 38 17 18 8 07 82 40 16 27 100 12
I Theoretical
II Gunmson Co , Colo
Its crystals are usually tabular parallel to oo P ob (oio) Their most prominent forms are ooPw (oio),— 2P66 (201), aPoo (201), oP(ooi), ooF(iio), 2? OD (021) and P(Tn) (Figs. 243 and 244). The angle no A i7o=43° 56' Twins are known, with oP(ooi) the twinning plane, The cleavage is perfect parallel to oopSo(oio) and the fracture is uneven or conchoidal.
The mineral has a glassy luster, which becomes pearly on oo p So (oio),
Hydrated Silicates
It is colorless, white, yellow, brown, pink or red. Its streak is white. It is brittle, has a hardness of 3-4 and a density of 2 2 For yellow light, i 4998, i 5003, 7=1 S°7°
Before the blowpipe heulandite whitens, exfoliates, crinkles and melts to a white glass It yields water in the closed glass tube and becomes dull and opaque It is decomposed by hydrochloric acid with pre- cipitation of pulverulent or gelatinous silica Its powder reacts alkaline
Heulandite is distinguished by its crystallization and its reactions before the blowpipe
Syntheu* — Crystals have been made by heating anorthite powder to 200° with gelatinous silica in water containing carbon dioxide
Fig 243 Fig 244
FIG 243 — Heulandite Crystal with P3b , oio (b)t P, no (w), aPoS , 201 (s)9
— 2P oo , 201 (/) and oP, ooi (t) FIG 244 — Heulandite, var Bcaumontitc Forms same as in Fig 243
Occurrence — The mineral occurs in the cavities of porous basalts, and occasionally in gneisses and granites, associated with other zeolites It is found also in some ore veins
Localities —Good crystals occur in the druses and veins in volcanic rocks at Fassa, Tyrol, at Montecchio Maggiore, Italy, at Lake Mien, Sweden, and along the north shore of Lake Superior It also occurs in druses m gneisses at the Campsie Hills, Scotland, and at Jones Falls quarries (beawmonfote), Baltimore, Md,
Philhpsite ((Ca
Phillipsite is a calcium, potassium alummo-sihcate with the theoretical composition indicated in line I. The composition of a specimen from Richmond, Australia, is shown in line II Many specimens contain barium and sodium.
448 Descriptive Mineralogy
Si02 A1203 CaO Na20 K20 H20 Total
I 48 8 20 7 76 64 16 5 100 oo
II 45 60 22 70 4 52 4 51 6 05 16 62 ioo oo
The mineral crystallizes in the monochmc system the a\ial latio 7095 . i ' i 2563 and 18=124° 23' Its crystals arc ncvei simple but are always twinned parallel to oP(ooi), forming groups with an ortho- rhombic or tetragonal habit (Fig 245) These are often twinned again with P ob (on) the twinning plane, producing intcrpenctration fourhngs (Fig 246A) Three fourhngs twinned again, with oo ?(no) the twinning plane, result in a group of 12 individuals (Fig 246 B) The individual crystals are usually bounded by oP(ooi), ooPob (oio) and
A Fug. 245 Fig 246
FIG 245 — Phillipsite Tnterpenetration Twin about oP(ooi) Forms arc oP, oot
(c), oo P Sb , oio and oo P, no (m) FIG 246 — Phiihpsite — A Fourlmg of two twins like FIJJ ,445 twinned again about
pob (on) The c faces are on the oulbidc. B Three fourhngs twinned about
ooP(no)
though oo Poo (ioo), ooP2(i2o) and several othoi forms also occur on them The angle iioAiTo= 6o°42/ The faces oo p(i 10) and oo P So (oio) are usually striated parallel to the edge between the two JBcftidcs occur- ring m distinct crystals the mineral is also found in radially fibrous glob- ular aggregates
Phiihpsite has a glassy luster, is colorless or white, yellowish, gray- ish, reddish or bluish, is transparent or translucent ami has u white streak. Its cleavage is distinct parallel to oP(ooi) and ooPob (oio). It is brittle, has a hardness of 4 and a density of 2.2, Itb refractive index, 0=i 51.
Before the blowpipe it fuses to a white glass In the closed glass tube it gives off water and becomes cloudy and milky. It is decomposed in HC1 with the separation of gelatinous silica, and in dilute HgSO* without precipitation
Hydrated Silicates
It is distinguished by its crystallization and by the fact that it dis- solves in KfeSCU without precipitation of BaSQt (see Harmotome, below)
Synthens —Crystals of philhpsite have been produced by heating potassium alummate and silicate in a closed glass tube at 200°
Localities — The mineral occurs m the vacuoles of basic igneous rocks at the Giant's Causeway, Ireland, at Capo di Bove, near Rome, Italy, at Aci Castello, m Sicily, and at various points m the state of Victoria, Australia
Harmotome (H2(Ba K2)Al2(SiO3)5 5H2O)
Harmotome is a barium compound almost identical in crystallization with philhpsite
Its theoretical (I) composition (also written (Ba KAfeSisOu sHgO) and the analysis of a specimen (II) from Thunder Bay, Canada, are shown below
Si02
I 46 64
Ii 46 36
A1203
Is 78
CaO
BaO
H20
H 54
Total
The crystallization and twinning of harmotome are the same as m
philhpsite Its aial ratio is 7032 i : i 2310, with 50' The
crystals more commonly contain the form
oo P 56 (100), and a few more orthodomes
Fourhngs are common, but m these the planes
oo P So (oio) form the outside of the group,
whereas m philhpsite the outside planes are
oP(ooi) The planes oop(no) and ooPoo
(oio) are striated as in philhpsite (Fig
247)
In gencial appearance and physical prop- erties harmotome resembles philhpsite It FIG 247— Harmotome Four- has, however, but one distinct cleavage, which ling Twinned like is parallel to oo P 8b (oio) Its hardness is 4-5 and density 25 Its icfractive indices are 1.503, 7=1 508 It acts very much like philhpsite before the blowpipe and m the closed tube It, however, dissolves readily in HC1 with the separation of pulverulent silica, and in dilute HsSCU with precipitation of BaSO. Its powder reacts weaklv alkaline
itc, ft 246 A, that Commonly the /; Faces are on Ihe Outside Note differences m direc- tions of strutions on this figure and 246 A,
Descriptive Mineralogy
The mineral is distinguished from all others but philhpu 'e by its crystallization, and from this mineral by its reaction with HSOi
It occurs m the vacuoles of volcanic rocks, in gneisses, giamtic rocks and a few ore veins
Localities — It is found at St Andreasberg m Har/s, m veins m granil e at Strontian, m Scotland, in druses m the syenite near Christianui, Norway, on calcitem mines at Rabbit Ml , and in the Beaver Mine, near Thunder Bay, Ontario, and in the gneiss undei New York City
Stdbite (Ca Na2)Al2Si,,0, o-eEkO)
Stilbite, or desmmc, is found in twinned nystals with <ui ortho- rhombic habit resembling the simple twins of philhpsite, and in sheaf-
Fro, 248.— Slicaf-hke Abrogates
like aggregates (Fig. 248), in radiating bundles and in thin platy prisms
Its composition calculated from the formula given above is as in I The result of the analysis of a soda-free specimen from French Creek Mines, Pa , is given m II and of a sodium-bearing specimen from Golden, Colo , m III
Si02 A1203 CaO MgO Na20
I 57 4 16 3 77 4
II. 58 oo 13 40 7 80 1/40 tr.
III 54 67 16 78 7 98 ,i 47
HaO Total
17,2 100,00
'8 30 99,93
19 16 too 06
The crystals are monoclinic (prismatic class), with an axial ratio of 7623 : i : 1.1940, with p~i2g° 10', They are always interpencf ration twins, with oP(ooi) the twinning plane as m phillipsitc Th<; indivicl-
Hydrated Silicates 451
uals are simple combinations of oopSb(oio), oP(ooi) and ooP(iio), and they are usually tabular parallel to oo P So (oio) Their cleavage is perfect parallel to oo P So (oio) and imperfect parallel to oP(ooi)
Stilbite is colorless or white, grayish, greenish, yellowish, red or brown It has a white streak and a glassy luster that is nearly pearly on oo P So (oio) It is transparent or translucent, is brittle, has a hardness of 3-4 and a density of 2 2. Its refractive indices are a=i 494, 1498, 7=1 500.
Before the blowpipe it exfoliates, swells and crinkles to a white blebby glass In the closed tube it yields water and becomes cloudy and opaque It is decomposed by HC1 with the production of pulverulent silica Its powder reacts alkaline.
Occurrence — Stilbite occurs m the vacuoles of amygdaloidal basalts, m veins cutting granites and other coarse-grained rocks, and on the walls of cracks in gneisses and schists It occurs also as deposits around hot springs
Localities. — Its principal localities are the basalt rocks of the Isle of Skye, Arran in Scotland, Mourne Mts and the Giant's Causeway, in Ireland, and the Deccan, in India It occurs m veins at Radauthal in the Harz, at Stnegau, in Silesia, and at Falun, m Sweden It is abun- dant in the old volcanic rocks of Nova Scotia; of Lake Superior, and of Table Mt , near Golden, Colo , and near Bergen Hill, N J , and is present in cavities in gneisses at several points in Connecticut and Pennsylvania.
Laumontite (CaAl2(SiO3)4-4H2O)
Laumontite occurs in monochmc crystals and in radiating fibrous aggregates Its formula demands the composition shown m I The analysis of a specimen from Table Mt , Colo , is quoted in II*
Al20s Fc20a CaO Na20 KaO H20 ToUl
I 51 07 21 72 It 90 Is 31 100 00
II 51 43 21 52 94 ii 88 19 35 13 81 xoo.ia
Its crystals are usually very simple monoclmic (prismatic class), combinations with an axial ratio 1 1451 : i : 5906 with £—99° 18' The most common forms observed are oop(no) and 2P6o (201), and often these are the only two present (Fig. 249) Frequently crystals of this type are twinned parallel to oopoo (100). Their cleavage is perfect parallel to oo P & (oio) and oo P(iio1 The value in A ilo=93° 44'.
Laumontite is white, grayish, yellowish or reddish, and has a glassy
Descriptive Mineralogy
luster except on cleavage surfaces On these it is pearly It is trans- parent or translucent <ind its streak is white It is buttle, has a hard- ness of 3-3 s nd ti densily of 23-24 Its refractive indices are 1,513, £=1,524,
Before the blowpipe it swells and melts to a white glass It gelatinizes w it h HCl It readily yields some water at low lempcrature in a closed tube, but a red heat is required 1o dnve off the last
FIG 249-Lauraontite Crystal with °oP, no (m) and 2P, 201 (c)
,1,1 ,
to &norlhitc and a pyroxene mineral.
Laumontite is best recognized by its crystals Occurrence —It occurs m the cavities of basic
volcanic rocks It is also found in veins in clay slates, and schists
and as a gangue mineral m certain ore veins.
Locahties —Its best known localities are 1he Isle of Skye and Dum-
bartonshire, m Scotland, in the Zillcrthal, Tyrol; at Table JVft , Colo ;
at Bergen Hill, N J , at many points on the north shore of Lake Superior,
and on Keweenaw Point, on the south shore, and m the trap rocks
near Annapolis, Nova Scotia
Scolecite (Ca(A10H)2(Si03)3 2H0)
Scolecite is white and it occurs in silky, fibrous ami dense radiating masses and also in crystals that are often aggregated into divergent groups (Fig. 250)
Its formula (written also CaAbSiaOio sHhO), demands the composi- tion indicated in I. The analysis of a specimen from Table Mt., Colo , is quoted in II
SiOs
I 45 92 Ii 46 03
AbOs
Fe203
.'27
CaO
NagO KgO
Total 13 75 100.00 14,48 100,00
The mineral is monoclmic (domatic class), with a : b : c ,9764 : i : 3434 and $=90° 42'. Its crystals are columnar or acicular m the direc- tion of c and are usually bounded by oo P So (oio), oo £(110), — P(IIT) and P(nx) (Fig, 251) Other planes are sometimes present in the pris- matic zone, and -P 66 (101), -3P(33i) and -3P3(i3i) at the termina- tions. Twins are more common than simple crystals, the twinning plane being oo P (100) and the composition plane the same* The angle 88° 37'
Hydrated Silicates
Scolecite is glassy in luster, transparent or translucent, and colorless or white. Its cleavage is perfect parallel to oo P(nol and its fracture
FIG 250 — Divergent Groups of Scolecite Crystals from near Bombay, India
conchoidal or uneven. Its hardness is 5-5 5 and density 2.2-2 4 Its crystals are strongly pyroelectnc On a cooling crystal the front pris- matic faces (no) are positively charged and the corresponding back faces (ilo) negatively charged. Their hemihednsm is brought out clearly by etch figures The refractive indices for yellow light are: a=i 5122, j8i 5187, T=I 5*94-
Before the blowpipe scolecite crinkles and fuses to a white blebby enamel. In the closed tube it yields water and becomes white and opaque It gelatinizes with acids
Scolecite is distinguished by its crystalliza- tion
Synthesis —Scolecite has been obtained by treat- ing natrohte (p 454) with a solution of CaCfe* Crystals occur on Roman tiles that have been ex- posed for centuries to the waters of the hot springs at Plombieres, France
Occurrence — It occurs in the cavities of basic volcanic rocks and in veins in crystalline schists.
FIG 251 —Scolecite Crystal with oop,
(ft), P, in to, and -P, in (a) Twinned about oo P oo (too)
Descriptive Mineralogy
Localities —Its principal occurrences ate veins in siliceous rocks in Canton Uri, Switzerland, and in the cavities of basalts m the Bern Fjord, Iceland, atStaffaand the Isle of Mull, Scotland, at Table Moun- tain, near Golden, Colo , and in the Deccan, India
Watrohte (Na2Al(AlO)(SiO3)3 2H2O)
Natrolite occurs in acicular crystals, and in ia<hal fihious, gran- ular and dense masses
Its theoretical composition (I) and the analysis of a specimen (II) from Magnet Co\e, Ark , coricspond veiy closcl}
Si02
I 47 36 Ii 47 56
FcO CaO MgQ NaoO
09 15 40
HaO
9 (M
Total 100 oo
Natrolite is orthorhombic (bipyramidal class), with a ft 9783 :i- 3536 and ooP(no), ooPoo(ioi), ooP2(r2o), co p (oio), P(m) the most commonly occurring forms (Fig 252) Additional forms that are fairly common are PJI (ii io.ii), 3P(33i ) an(l 33(*3i) The prismatic angle is nearly 90° (88° 45'), causing the crystals to appear tetragonal Some crystals are apparently monodimc (prismatic class) with 0=<jo° 5', in which case the substance is dimorphous. The habit of the crystals is columnar, or ancular, m the direction of the c axis with Ht nations on the prismatic planes parallel to this direction. In the case of a few crystals from Norway, how- ever, the elongation is m the direction of b. Twins are known, with $P (301) the twinning plane.
Natrolite is glassy and transparent or translucent. Tt is colorless or white, yellowish, reddish or green Its streak is white. Its cleavage is perfect parallel to ooP(no). Its fracture is uneven or runchoidal, its hardness 5-5 5 and density 2.2-2 5. Its refractive indices for yellow light are ai 4754, ]8-i 479° 14887-
Before the blowpipe the mineral fuses quietly to a colorless glass at the same time coloring the flame yellow. In the closed tube it loses water and becomes cloudy and opaque. Its powder reacts alkaline
Natrolite is easily distinguished from other zeolites, by its crystallisa- tion and action before the blowpipe
Syntheses,*— Crystals of natrohte have been obtained by dissolving
FIG 252 —Natrolite Crystals with ooP, no (tn)t P, in (0), Poo, oio (6) and Pfj, ii 10 ii
Hydrated Silicates 455
the powdered mineral in a closed tube with carbonated water at 160° and cooling Crystals supposed to be those of natrohte have been pro- duced by treating nephelme in a closed tube at 200° with a solution of alkaline carbonates in carbonated water
Occurrence — The mineral occurs in the cavities of volcanic rocks, and as an alteration product of nephelme, sodalite and plagioclase m coarse- grained rocks
Localities — Crystallized natrohte is abundant in the volcanic rocks of Hegau and the Kaiserstuhl in Baden, m the basalts of Silesia and Bohemia, in the volcanic rocks of Tyrol and Italy, in those of the Auvergne, France, in veins in the syenites of Langesundfjord, in Nor- way , m the basalts of Cape Blomidon and other points in Nova Scotia, at Eagle River, in Michigan, and Bergen Hill, N J , and in the nephe- lme syenites of Magnet Cove, Ark,, and elsewhere,
Thomsonite ((Ca Na2)Alo(Si04)2 2jH2O)
Thomsomtc, or comptomte, is evidently an isomorphous mixture of soda and lime molecules — the ratio of Ca to Nd2 varying between 3 i and i i The calculated composition represented by the formula (Ca Na2) Al2(SiO-i)2 2§H20 is given in III In I is given the calculated formula of the compound in which Ca : Nag is as 3 ' i and m II, that m which this ratio is 2 i The analysis of tabular crystals from the basalt of Table Mt , near Golden, Colo , is given in IV.
A1203 CaO Na20 H20 Total
L 37 o 31 4 12 9 48 13 9 100 oo
II 36 9 31 4 11.5 64 13 8 100 oo
III 36 8 31 3 86 95 13 8 100 oo
IV 40 68 30 12 ii 92 4 44 12 86 100 02
Thomsonite crystallizes in the orthorhombic system with a : b : ,9932 : i i 0066 The crystals, which are rare, usually have a pris- matic habit. They are bounded by oo P 60 (100), oo P(no), oo P 06 (oio) oP(ooi), 4? oo (401), 8P 60 (801), and often 06 (012), and are striated parallel to c (Fig. 253). The angle 110 A 110=89° 37'. The crystals are commonly grouped in radial aggregates or spherical concretions. Rarely, the mineral is in fine-grained structureless masses
Thomsonite has a glassy luster that in some cases is slightly pearly, especially on cleavage planes It is transparent or translucent, colorless, white, gray, green or red and has a colorless streak. Some radial aggre- gates are red and white in concentric zones. The cleavage of thorn-
Descriptive Mineralogy
sonite is perfect parallel to oo P 56 (oio) and less pcifect parallel to oo P6o (ioo) Its fracture is uneven It is buttle, has a hardness of 5-5 5 and a density of 2 3-2 4, and is pyro- electric Its refractive indices aie 01=1498,
FIG 253 — Thomsomte Crystal with cc P no (w), oopso; 100(0), oc P 00,010(6), SPoc,
8oi(e),4P,40i(</) and oP, ooi (c)
Before the blowpipe it swells and fuses to a white glass In the closed tube it gives up \\ater and becomes opaque It gelatinizes with HC1 Its powder icacts alkaline
Lmtomte is a green, piehnite-hkc variety occurring as little structureless pebbles on the north shore of Lake Supcnoi It is used to some extent as a gem stone Its hardness is 5-6, and its sp gr 2 34
Chlorastrolite is a fibrous variety, also oc- curring as pebbles on the shores 'of Lake Superior, especially on Isle Koyalc It is often pink and white in concentric zones It also is employed as an orna- mental stone Some of the chlorastrolite is piobably fibrous piehnite
Occurrence — The mineral occurs in the vacuoles m igneous rocks, as a constituent of pegmatite dikes, and as an alteration product of nephchne m nephelme rocks, and of the plagioclases m crystalline schists It is found also as little pebbles on the north shore of Lake Superioi, where it was washed from amygdaloidal basalts
Localities — It is found m the basalt of Kaaden and othci places m Bohemia, in the porphyries of Kilpatnck, Kilnulcom and Port Glasgow, in Scotland, m the inclusions m the lavas of Mte Somma, near Naples, Italy, in veins on Laven, Aro and at other places in Norway, in the basalts at Port George and Cape Split in Nova Scotia; on the shore of Lake Superior near Grand Marais, Minnesota, where it originally filled amygdaloidal cavities in diabases and basalts; in cavities in the neph- elme syenites at Magnet Cove, Ark , and in the basalt at Table Mt near Golden, Colo
Production —Chlorastrolite to the value of $350 was sold during
Chabazite ((Ca Na2)Al2(Si04j)6HoO)
Chabazite has a variable composition It is probably an isomor- phous mixture of the Ca, Na and K molecules corresponding to the general formula (R"R'2)A12 (8103)4 eHgO, Analyses of the three chemical types of the mineral are given below,
Hydrated Silicates
Si02
I 43 84
Ii 47 S2
Iii 49 24
Ai203
Fe203
CaO
MgO Na20
K20
Total
S
S 78
Ioo
Os
I Phacohle from Richmond, Victoria
II From the basalt of Table Mt , Golden, Colo Also 43 SrO III Haydenite from Jones Falls quarry, Baltimore, Md Also i 47 BaO
Chabazite occurs in crystals and in compact aggregates It crys- tallizes in the rhombohedral division of the hexagonal system (ditngonal scalenohedral class), with a : i i 0860 Crystals are usually of a cubical habit because of the predominance of the rhombohedron which
Fig 254
Fig 255
Fig 256
FIG 254 — Chabazite Crystal with R, toll (r), — ]R, oils (e) and — sR7 0221 ($) FIG 255 — Chabazite Interpenetration Twin, with c the Twinning Axis and oR(oooi)
the Twinning Plane
FIG 256 — Phacolite with Same Forms as in Fig 254 and also oR, 0001 (c), JP2, 1123 (/) and — 3R 0223 (p) Interpenetration twin about oR(oooi)
has nearly equal a and c axes Besides R(io?i), the most common forms are oR(oooi), — £R(ox72 and — 2R(o22i) (Fig 254), though other minus rhombohedrons, scalenohedrons and a prism (ooP2, 1120) and pyramid (|P2, 1123) of the second order are also known The angle ioTiAiioi=850 14' The crystals are often striated parallel to the edge between R and— -JR Twinning is not uncommon Both con- tact and Interpenetration twins are known, the former with R(ioli) the twinning plane, and the latter with oR(oooi) the twinning plane (Fig 255) In the variety of chabazite known as pkacohte, the crystal habit is lenticular because of the nearly equal prominence of f P2(ii23) and — 2R(o22i), and twinning parallel to oR (oooi) (Fig 256).
Chabazite is glassy in luster, is transparent or translucent, colorless or white, gray, yellowish or pink Its streak is colorless. Its cleavage
458 Descriptive Mineralogy
is distinct parallel to R(ioTi) and its fracture uneven Its hardness is 4-5 and density 2 08-2 16 Its indices of rcfi action are about
Before the blowpipe fragments of the mineral usually swell and fuse to a porous translucent glass In the closed tube they yield water and become cracked, but remain clear The variety from Victoria (phacohte), however, becomes cloudy and red and breaks into pieces The mineral is decomposed by HC1 and the separation of slimy silica, but after fusion is insoluble. Its powder reacts weakly alkaline
Chabazite is distinguished by its cryblalli/ation and its reaction in the closed tube
Syntheses. — Chabazite crystals have been obtained l>y dissolving the powder of the mineral in carbonated water in a closed tubck ut 150° and cooling, and by heating to 200° a nrnture of freshly pi capitated SiO, AbQs and Ca(OH)2 in water containing COa
'When chabazite is fused alone it crystallizes as anorthite
Occurrence — The mineral occurs in the vacuoles of basalt** and other volcanic rocks and on the walls of crevices m gneisses and schists It is found also in ore veins and as a deposit from thermal spi ings
Localities — It is abundant in nearly all regions in which basic vol- canic rocks occur, especially m Rhemsh Prussia, Hesse, Silcsiti, Bo- hemia, Tyrol, Italy; Canton Un, Switzerland, Kilrnalcolm and Skye, Scotland, Iceland, near Richmond, Victoria (phacohte), and elsewhere. In North America it occurs m the basalts m southwestern Nova Scotia, on the walls of clefts in a gneiss at Jones Falls and Baltimore, Md (haydemte], and in the basalt of Table Mt. and Golden, Colo.
Analcite (NaAl(Si03)2'H2O)
Analcite corresponds to the monohydrate of a sodium leucitc. Its formula demands the composition shown in I In II is given the analy- sis of a specimen from Table Mt , Colo Many analates contain small quantities of CaO In III as the analysis of calciferous crystals from the Highwoods Mts , Mont.
Si02 AkOs Fe203 CaO MgO Na20 K20 HaO Total
I 54 54 23 20 . . 14 OQ . , 8 17 loo oo
Ii 55 81 22 43 . 13 47 ... 8 37 100 08
III 54 90 23 30 tr i 90 70 10 40 I 60 7,50 100 30
Analcite forms isometric crystals that are usually ioofiltctrahcdrons, 202(211) (Fig. 257) More rarely they are modified cubes (Fig, 258),
Hydrated Silicates 459
containing ooOoo(ioo), ooO(no), 2000(210), 202(211), O(nr) and occasionally §0(332) and icositetrahedra with large parameters Some crystals show double refraction which is regarded as due to strain
The mineral has a glassy luster. It is transparent or translucent, colorless or white, gray, yellowish, greenish or reddish Its streak is white It possesses a very imperfect cleavage parallel to oo 0 oo (100) and an uneven fracture Its hardness is 5-5 5 and density 2 2-2 3 For yellow light, i 487
Before the blowpipe analcite fuses to a colorless glass, imparting a yellow color to the flame In the closed tube it yields water, but retains its form and luster. It gelatinizes with HC1 Its powder reacts alka- line
Analcite resembles leucite and light-colored transparent garnets It is distinguished from garnets by its less hardness and from leucite
Fit, 257 FIG 258
l'n. 257 — Analcite Crystal with 262, 21 1 (n) FIG 258 — Vnalutc Crystal with oo 0 00 , 100 (a) and aCb, 211
by the presence of water and by its easy fusibility. It diffeis fiom chabazite by fusing without intumescence to a colorless glass
Synthew — Crystals of analcite have been made by heating sodium silicate, or a hydrate, with an aluminous glass to i8o°~i9o° m a dosed tube, and by heating m a similar manner a mixtuie of sodium silicate and aluminate with hmewater. Crystals have also been obtained by heating to 500° a mixture of finely powdered laumontite with an aqueous solution of sodium silicate,
Occurrence — Analcite occurs as a primary constituent of certain alkaline volcanic rocks m the Little Belt and the Highwood Mts,, Mont , and elsewhere It occurs also filling cavities in volcanic lavas and as a secondary mineral, replacing nephehne, leucite and sodahte m both volcanic and plutonic rocks.
Localities — It is found in the vacuoles of basalts on the Cyclopean Islands, near Catoma, Sicily, m the Kaiserstuhl, Baden, In the Seisser
460 Descriptive Mineralogy
Alps, Tyrol, at Dumbarton, Old Kilpatnck and elsewhere m Scotland, at Bergen Hill, N. J , Table Mt near Golden, Colo , on Keweenaw Pt , Lake Superior, in southwestern Nova Scotia, and elsewhere It occurs m veins in southern Norway, in druses near Richmond, Victoria, and as an original component of igneous rocks in the Highwood Mts , and the Little Belts Mts, in Montana, near Cnpple Creek, Colo ; near Sydney, N S Wales, at Winchester, Mass , and elsewhere
Chapter Xxi The Titanates And Tit Ano-Sili Gates
THE titanates are salts of titanium acids that are in all respects anal- ogous to silicic acids Thus, the normal titanate is a salt of the acid H4Ti04 and the metatitanate a salt of metatitamc acid (H4Ti04-H20 =H2Ti03) The mineral, perovskite, for instance, is a calcium metati- tanate (CaTiOs) and tlmemte a ferrous metatitanate Dititanates are salts of H2Ti205(2H4Ti04-- 3H20 H2Ti205) There are no dititanates known among minerals, but there is one mineral which is fairly common that may be regarded as a dititanate in which one of the Ti atoms has been replaced by Si, giving rise to a titano-silicate This mineral is sphene, which is the calcium salt CaSiTiOs
Perovskite (CaTiOa)
Perovskite occurs almost exclusively in small crystals with a cubic habit Although apparently complexly modified cubes, they arc in fact complicated intergrowths of orthorhombic ' lamellae, with i i : 7071 (approximately)
The formula CaTiOs is equivalent to 41 i per cent CaO and 58 9 per cent Ti02, but the mineral usually contains also some Fe
The cleavage of perovskite is cubic Its fracture is uneven to con- choidal It is brittle, has a hardness of 5 5 and density of 4 02 Its color varies from pale yellow through oiange-yellow to reddish brown and grayish black Its streak is coloiless and luster adamantine The mineral is transparent to opaque Its refractive indices for yellow light are about 2 38.
Perovskite is infusible m the blowpipe flame. The salt of phos- phorus bead in the oxidizing flame is green while hot, colorless when cold In the reducing flame it is green-gray when hot, and violet blue when cold The mineral is completely soluble m hot H2S04.
It alters to ilmenite and magnetite, and possibly anatase.
Syntheses —Crystals have been formed by heating a mixture of Ti02, CaCOs and an alkaline carbonate until all the alkali volatilized, and by fusion of TiOs, CaCOs and CaCl2
462 Descriptive Mineralogy
Occurrence and Localities —Microscopic crystals of perovslute occur in some igneous rocks, where they aie probably separated from the magma producing the rock It also occurs in chlorite schist and lime- stone as small crystals embedded in the rocks, and also implanted on the walls of cracks at the Achmaton Mine in the District Slatonst, m the Urals, near the Fmdelen glacier near Zernutt, Switzerland, m Val Malenco, Italy, at Magnet Cove, Arkansas, in coarse-grained, nephelme syenite, and associated with magnetite m great quantity at Catalao, Goyaz, Brazil
Ilmenite (FeTiO)
Ilmemte or menaccamte, is one of a series of isomorphous compounds consisting of the titanates of Mg, Mn and Fe, all of which crystallize m the rhombohedral tetartohedral division of the hexagonal system (trig- onal rhombohedral class) The crystallographic constanth of ilmemte are, however, so nearly like those of the mineral hematite, which is ditngonal skalenohedral, that the two compounds often nystalhze together, and consequently many specimens of ilmemte when analyzed show notable quantities of Fc20. These are rcgaulcd as solid solu- tions of Fe20s in an isomoiphous mixture of FeTiOa and MgTiQa The axial ratios of the two mmeuilb are:
Ilmemte a ' c=i : i 385. Hematite a 6 1 1365
The composition corresponding to the above formula is Ti3i6 per cent, Fe"— 368 per cent and 0=31,6 per cent, but the mineral nearly always contains some Mg and ferric iron (FVaO,*) An analysis of ilmemte separated from a pendotite in Kentucky gave:
Ti02 FeO MgO FcsOa AljjOa SiOu Other Total 49 32 27 81 8 68 9 13 2 84 76 1.56 100 10
Ihnemte is rarely found m crystals. It is usually in large homo- geneous masses, in granular aggregates, in thin plates and m sand grams. The crystals have a tabular or rhombohedral habit and resemble very
closely those of hematite. The predominant forms are R(ioTt), oR(oooi)
—(4223), -2R(o22i) and - JR(oi7a) (Fig, 259)- The angle loTi A
Ixoi=940 29' Simple crystals, bounded by oR(ooox), R(io7i) and — R(OIII) are also common
The mineral is black and opaque, and its streak is black to brownish
Titanates And Titano-Silicates 463
red Its cleavage is parallel to oR(oooi), and its fiacture conchoidal It has a submetallic luster, a hardness of 5 to 6, and a specific gravity of 4 5-5 It is slightly magnetic, and is a good conductor of electricity
Before the blowpipe ilmemte is nearly infusible. It gives the reac- tions for iron with beads When the micro- cosmic salt bead, which is brownish red in the reducing flame, is treated with tin on charcoal it changes to a violet-red color. The pulverized mineral is slowly dissolved in hot HC1 to a yellow solution If this is filtered and boiled with the addition of tin it changes pIG 259 —Ilmemte Crystal to blue, indicating titanium with R, ioli (r), oP,
Ilmemte can be distinguished from hema- QQOl / ffi2 -- /w\
tte by its streak, from magnetite by its . ' ,. i i r , . , f and — aR, 0221 0)
lack of strong magnetism and from most
other heavy black minerals by its reaction for titanium Upon weathering ilmemte alters to sphene and limomte Synthesis — Crystals have been obtained by melting together Ti02 and FeCl2
Occurrence — The mineral occurs as a constituent of many igneous rocks, and of the crystalline schists produced from them by meta- morphisni, especially of gabbros and diorites and their derived schists, where it has crystallized from the magma forming the original rocks. It occurs also in veins cutting these rocks and also as great masses near their contacts with other rocks In a few places it forms the mam com- ponent of sand
Localities — The mineral is found at many places where gabbros and diorites abound Its principal occurrences in Europe are in the Ilmen Mountains, Ural, at Menaccan, Cornwall, England, and at Kragero, Arendal and Snarum in Norway. In North America it is found as crystals m pegmatites at several points in Orange County, New York, at Litchfield, Connecticut, at Bay St. Paul, Quebec, and in large masses m the Adirondacks, New York, and in northeastern Minnesota
Uses — Because of its abundance, many attempts have been made to utilize ilmemte as an ore of iron, but on account of the large quantity of titanium in it, no satisfactory means of smelting it on a commercial scale have been successful, and consequently the mineral has little value at present. With improvements in the processes of electric smelting, however, it may before long become an economically important source of iron
464 Desciuptivk Min1Ghammsy
Titamte (CaSiTiOs)
Titanite, or sphene, usually occurs as crystals, but in some places in granular and compact masses Although the formula lor the mineral is simple, as given above, requiring as it docs 286 pci cent CaO, 408 per cent Ti02, and 306 per cent Si02, many specimens show also the presence of Fe20a, AhOj, and in many cases consulei.ihle cjuantities of
Y203
Analyses of three specimens fiom tlifleient localities yielded
Si02 Ti02 CaO FcjAs AbOi4 ViAi MnO Total
Zillerthal 32 29 41 & 26 61 i 07 , 101 55
St Marcel 30 40 42 oo 24 30 tr $ So too 50
The crystals are monoclimc (pnsmatic cLi,ss), with a : 7547 . i : 8543 and 0=119° 43' Their habit vuues widely Some ate
Fio 260— Titanite Crystal with <Poo, 100 (a), -JP&o, 10 (i) oot (r)
and JP, Iii (/) Fro 261— Titanite Crystal with a, a and as in Kig. 260. Also — 1>, m and
eol*, no (m) FIG 262 —Titanite Crystal with m, n and c as in Fig a6i. Also +1, In
double-wedge-hke, others are envelope-shaped, others prismatic, and others tabular On the wedge-shaped crystals iP(f u) and — JP eo (102) predominate (Fig* 260). On the envelope-bhapcd ones ooPoo(ioo), -P(iu) and oP(ooi) are most prominent (Fig, 361), umi cm the tabular ones oP(ooi) is the largest face (Fig, 262). The prismatic crystals are often more complicated In all about 75 forms have been identified Both contact and penetration twins arc common, with oo P fib (TOO)
Titanates And Titano-Silicates 465
the twinning plane The cleavage is distinct parallel to oo P(uo), and there is often, in addition, a very perfect paitme; parallel to — 2P(22i), which is due to polysynthetic twinning The planes oo P 5d (100) and 2-P(Ti2) are often striated parallel to their intersection with °° P(no) The angle noAiTo=66° 29'
The mineral is brown, gray, yellow, green, black, rose or white Its streak is white or pink, its luster is vitreous or resmoub and it is trans- parent, translucent or opaque Its hardness is 5-5 5 and gravity 3 5 It is pleochroic in yellow, pinkish and nearly colorless tints Its refrac- tive indices vary widely with the composition In a specimen from St Got hard, the indices for yellow light are a— i 874, /3= i 8940, 7=2 0093 The principal recognized vaneties aie
Titamte, opaque or translucent uith black or brown colors
Sphene, translucent, light-colored, brown or yellow
Ti tan omo) p/nte, white, granular alteration product of rutile or ilmemte
Gteenovtte, rose-red, translucent variety containing manganese.
When heated before the blowpipe the mineral iuses to a dark glass, its fusing point bemsj I2io°-i23o° With beads some varieties exhibit the reaction for manganese and all show the colors characteristic of titanium All vaiietics aie sufficiently soluble in HCl to give the violet- colored solution when Healed with tin, and all are completely decom- posed by HaSOi
Sphene is distinguished from itainolite and fat net by its crystalliza- tion and softness, from i/> alenle by its gi eater hardness, from other similarly coloiecl minerals by the reaction foi titanium
Upon decomposition' it yields calute, magnetite, rutile and other oxides of titanium and ilmemte
Synthesis — Crystals of titanite have been made by fusing SiCte and Ti02 with an excess of CaCIjj.
Occurrence — Spheric* is a widely spread constituent of igneous rocks where it has probably formed directly by crystallization from a molten magma, and is in many schists and limestones that have been meta- morphosed In the latter cases it is of metasomatic origin It occurs also as implanted crystals on the walls of cracks and cavities in acid granular rocks, under which conditions it is pneumatolytic. Further, it is a common decomposition product of ilmemte and rutile*
Localities — The mineral occurs so widely spread that even its prin- cipal localities are too numerous to mention here Particularly fine crystals are found at Ala and Marcel, in Piedmont, at various points
466 Dehckiptivk Minehalo(!Y
in the Zillerthal, Tyrol, at Zoptau, in MOM via, near Tavistock and Tremadoc, in Wales, at Sandford, Maine, at unions points in Lewis, St Lawrence and Orange Counties, New Yoik, pnncipally m lime- stones, at Franklin Furnace, New Jersey, also in limestone, in Iredell Buncombe and Alexander Counties, North Carolina, and near Egan- ville, Renfrew County, Ontario
Part Iii Determinative Mineralogy
Chapter Xxii
General Principles Of Blowpipe Analysis
Determinative Mineralogy.— Minerals are identified by means of their chemical and physical properties A mineral specimen may be analyzed by the ordinary methods of chemistry This procedure will reveal its empirical composition but it will not distinguish between dimorphs For this other means must be relied upon, and of these the most convenient are those based upon physical properties
Since chemical analysis in the ordinary way is a long and tedious process, requiring bulky reagents and laboratory apparatus, it is not applicable in the field or when rapid determinations are desired Conse- quently, chemical analyses are employed only when other methods of determining a mineral are inadequate or when the accurate composition of the specimen is desired
The usual methods of determining minerals employed by mineral- ogists are based on their physical properties and upon blowpipe tests, the latter being utilized to differentiate substances with nearly similar physical properties,
Blowpipe Analysis. — By means of the high temperatures that may be secured with the aid of the blowpipe, many chemical reactions may be made to take place which are impossible at ordinary temperatures. The reagents used are few and generally m the solid form, and conse- quently may be made to occupy little space Many of the reactions arc delicate and characteristic of the different elements and most of them may be made rapidly and with small quantities of material* The results are qualitative only, but when combined with the study of the physical properties of the substance tested, they are usually sufficiently definite to enable one to recognize its nature In a few instances liquid
Determinative Minmk Al( )( ! Y
reagents must be employed to gu e decisive icsults, but they aic few and easily obtained
The Blowpipe.—The blowpipe (Fig 26,0, in its simplest foim, is a tube with a small outlet through which a an rail of dir may be directed through a flame upon a small particle of subbtancc A puctical mitru
FIG. 263 —Simple Blowpipes
ment consists of a mouthpiece, a tube, an an -chamber to catch moisture a side tube and a tip pierced by a small hole. The tip is placed m the flame of a Bunsen burner, an alcohol lamp 01 some otlici source of flame and a current of air is blown through it by placing the mouthpiece to the lips, breathing full, and allowing the contraction of the cheeks to force — thc nir fiom the mouth Other
forms of blowpipe are advocated for special purposes Frequently the side tube is curved in such a way that the air passing through It is heated before it issues from the tip and a hotter flame is pro- duced than is possible with the simpler instrument,
Since it is often desirable to have the hands free to manipulate the assay, the blowpipe is some-
264 -Bellows for Use with Blow. pipe If intended to be worked by
- -
Blowpipe Analysis 469
pressure required to force the air from the reservoir is applied by the foot
Source of Heat.— The best source of flame for general use with the blowpipe is the Bunsen burner supplied by ordinary gas, and furnished with a tip which is flattened at the upper end and cut off obliquely The blowpipe is supported on the upper end of this tip and pointed downward parallel with it Thus, the flame is blown down upon the assay
Since, however, illuminating gas often contains noticeable traces of sulphur, for the detection of this substance it is often advisable to sub- stitute an alcohol lamp for the gas burner With the alcohol should be mixed a little turpentine in the proportion of one part of the latter to twelve of ttu° former to increase the reducing power of the flame
Supports. —The principal supports used to hold the material under investigation — the assay — are charcoal, platinum, and glass Sheets of aluminium, plaster slabs and unglazed porcelain are also sometimes em- ployed, but for most purposes the first three are entirely adequate
Charcoal. — Charcoal is used in reduction tests and m the study of sublimates It should have a flat surface and should be well burned
Platinum. — Platinum is used principally m the form of wire and foil The wire should be of about the thickness of coarse horsehair ( 4 mm ), and should be fused into a 3-mch long glass tube to serve as a handle It is employed mainly in the production of colored glasses or beads The foil should be thin When about to be used, it should be bent into a shallow cup m which mixtures may be fused
Glass.— Glass is used m the form of tubes These should be of a hard glass about 90 mm long and 6 mm inside diameter When closed at one end, they serve to hold substances which are to be heated to a high temperature in the study of their volatile constituents Tubes open at both ends are employed to study the effect of roasting the assay in a current of air
Other Apparatus. — Other pieces of apparatus desirable for satis- factory blowpipe work are A magnet, a magnifier, a pair of forceps, a small hammer, an anvil, a pair of cutting pincers, a piece of blue glass or a screen composed of strips of celluloid colored different shades of blue, or a hollow glass prism filled with indigo solution.
Reagents. — Since blowpipe tests are made on minute quantities of material, it is necessary that all reagents used be as pure as possible. Those most frequently employed are* Borax, Na2B40r loEfeO, microcos- ms salt, or salt of phosphorus, NH4NaHP04 4H20, fused sodium car- bonate, Na2C03, aad potassium sulphate, HKS04, , KNOs, cobalt
Determinative Mineralogy
ntfrate, Co(NOs)2 6H20, in solution, copper o\idc, CuO, magnesium ribbon, Mg, granulated zinc, Zn, sulphuric acid, HoSOi, hydrochloric acid, HC1, and blue litmus and turmeric papcn Other reagents are employed in special tests, but those mentioned above arc used generally The Blowpipe Flame.— The blowpipe flame is used not only for producing a high temperature, but also to produce o\idi/mg and reduc- ing effects The oxidizing flame aids m adding oxygen to the substance heated and the reducing flame abstracts it
A luminous flame, such as is produced by a candle or a Bunsen burner, with the airholes at the foot of the tube closed, consists of (c) an inner, non-luminous cone (Fig 265) containing unigmtcd gas, (&) a luminous envelope surrounding this, m which there is paitul combustion of the gas passing out from the nonlummous cone, and an outer purplish mantle
Because protected from the air by the outer mantle, the gas in the luminous inner cone is not entirely consumed The available ovygcn combines with the easily combustible hydrogen, while the carbon of the gas is separated m extremely fine piuticles These are at a high temperature and arc, therefore, incandescent In this condition, carbon is an active reducing agent, combining with oxygen readily, ab- stracting it for this purpose fiom any oxygen-bearing compound with which it is brought in contact Con- sequently this portion of the flame exerts a reducing action upon anything within its sphere. In the outer mantle, there is an abundance of oxygen This combines with the carbon par- tides as they pass out from the luminous envelope, forming, at first, carbon monoxide, CO This unites with more o\ygen forming carbon dioxide, C02, and giving a blue flame. Since the temperature in this portion of the flame is very high and there is an abundance of oxygen present, substances subjected to its action are oxidized.
The use of the blowpipe accentuates the effects of the different por- tions of the flame and serves to direct it upon the particle to be tested
To produce the reducing flame (R F ), the blowpipe jet is placed at the edge of the burner flame near its base, and a gentle current of air is blown (Fig 266) This deflects the flame without mixing too much oxygen with it— and it remains luminous. Its most energetic part is near the end of the luminous cone (<z).
The oxidizing flame (O.F ) is produced by passing the tip of the blow-
FIG 265 — Candle Flame, Showing Three Mantles
Blowpipe Analysis
pipe into the flame a short distance (Fig 267) and blowing strongly, but steadily A sharp-pointed, nonlummous flame results, with an inner blue cone The most effective oxidizing area is just beyond the tip of the inner blue cone
Before attempting to use the blowpipe for producing oxidizing and reducing effects, the two flames should be practiced with until they can be manipulated with certainty The reducing flame is the most difficult to use successfully. It must be maintained unchanged for some time and the assay must be completely enveloped m it to secure satisfactory results. Otherwise, oxidation may ensue. In order to test one's ability
FIG, 266 —Reducing Flame.
tie. 267 — Oxidizing Flame
to reduce with the blowpipe flame, a little borax should be melted in a small loop made at the end of a platinum wire It will form a colorless glass Into this should be introduced a tiny gram of some manganese compound If the borax with the added manganese is heated in the oxidizing flame, an amethyst-colored glass will result This, if heated in the reducing flame, will again become colorless, but the color will return if the assay is touched by the oxidizing flame. When the colon can be made to disappear and reappear at will, the proper amount oi skill for the manipulation of the flames will have been attained
Use of the Closed Tube.— The closed glass tube is used to discover whether a substance contains water or not, to detect its volatile con-
472 Determinative Mineralogy
stituents, and to discover the natuie of its decomposition products It is also employed in the observation of cert din other characteristic changes m a substance produced by heating it to d hifljh temperature
The material to be tested is powdered and slid into the tube with the help of a little, narrow papei tiough, which is lone; enough to icdch nearly to its bottom The tube is then tapped to settle the nwtenal and the end containing the assay is heated, at fust gentlv, latei moie vigorously, even to redness, either in the burner flame 01 in the flame pioduced by the blowpipe
Water is indicated by the condensation of little drops on the upper, cooler portion of the tube If the water, when tebted litmus paper, reacts acid, a volatile acid (H2S04, HC1, HNO or UF) is indicated. If it reacts alkaline, ammonia has been evolved.
Gases— The charactei of the gases evolved is best recognized by their color and odor
(a) Hydrogen sulphide (H2S) is recognized by its odor It indicates a sulphide containing water
(V) Nitrogen peroxide (NA) recognized by its reddish brown fumes and its characteristic odor It indicates a nitrate or a nitrite In the case of HN03, the reaction is 2HNOi-0+H/)+NA
(c) Hydrofluoric acid (HF) attacks the glass of the tube and etches it, Its presence in the assay indicates a fluoride
Sublimates or coatings may be deposited In the cooler portion of the tube
(a) If white, they may indicate ammonia salts, antimony trioxide, arsenic tnoxide or tellurium dioxide
(b) If gray or black, they indicate arsenic, mercury or tellurium
(c) If black j while hot, and reddish brmmi.whm (old, antimony sulphide; and if reddish brown, while hot> and reddish yellow, when told, arsenic sulphide,
Changes of Color are very characteristic for certain substances, the following being of greatest importance
(a) From white to yellow and to while again on cooling: zinc oxide. (&) From white to browmsh red and back to yellow* lead oxide,
(c) From white to orange-yellow and back to pale yellow when again cold: bismuth oxide
(d) From red to black and red agam when cold: mercunc and ferric oxides. The mercury oxide is volatile
Use of the Open Tube.-— The open tube is used when it is desired to treat the assay with a current of hot oxygen. It is charged in the same manner as the dosed tube, the assay being placed about 12 mm, from
Blowpipe Analysis 473
the end The tube is then held in the forceps over the flame, care being taken to incline it slightly for the purpose of producing an upward cur- rent of hot air By this means, the following substances are easily detected
Sulphur is detected by the choking odor of SOj
Arsenic yields a white volatile sublimate, which disappears upon heating
Antimony gives white fumes which may partly condense on the cooler portion of the tube as a white sublimate and partly escape from its end The sublimate is only slightly volatile
Mercury yields globules of mercury
Tellurium yields a white sublimate, which, when heated, fuses to colorless drops
Selenium gives a sublimate which is white 01 steel-gray near the assay (SeOj) and red at a greater distance (SeO and Se) The odor of the volatile metal is exceedingly disagreeable If the tube is allowed to discharge through the flame, it will produce a blue color
The Use of the Charcoal. — A shallow depression is made near one end of a piece of charcoal, the powdered assay placed m this, and the
FIG. 268 —Proper position of charcoal
blowpipe flame played upon it, while the charcoal is held in a tilted position by the left hand (Fig 268) If the assay decrepitates when heated, it should be moistened with a drop of water The principal phenomena to be noted are. Volatilization, fusibility, decrepitation, deflagration, odor, reduction and the production of sublimates.
Volatilization —The substance vaporizes and disappears Fusibility —The substance melts entirely, or partially, in the different parts of the flame, some substances fusing easily and others only with great difficulty
Decrepitation — The substance flies to pieces when heat is applied, indicat- ing decomposition or the presence of water, or included gases
474 Determinative Mineralogy
Deflagration —The substance suddenly burns httle explosions charac- teristic of nitrates
Reduction and Sublimation — When heated on chaicoal with the RF, some substances may easily be reduced to the metallic state, otheis are i educed with difficulty Thus, 2PbO+C=Pb2+CO. Reduction takes place most readily if the assay is powdered and mixed with about four times its volume of dry sodium carbonate (NasCO) Thus
2PbS+ 2Na2CO-,+ C
In cases of great difficulty, a little potassium cyanide ' (kCN) or borax (Na2B407 ioH20) added to the mixture will frequently hasten the result In any case, the heat must be applied until nearly all the assay sinks into the charcoal
When sufficiently heated, some substances yield a globule of metal, others are completely volatilized, others yield fumes, produced by the oxidation of portions of the assay, while yet others aie partly reduced to a globule of metal and partly volatilized Thus, during the reduction of PbS, some of the lead may be oxidized according to the reaction
PbS+Na.COi Noib+PbO+COj,
and a portion of the oxide may settle on the coal When fumes are pro- duced, they are deposited upon the coolei portions of the charcoal in the form of sublimates which possess characteristic properties
Gold, silver, and copper compounds yield globules of metal without sublimates The metals are separated fox examination by cutting out the charcoal beneath the assay, and crushing I he mass with water in a small mortar Upon pouring ofT the watei, the metal remauis as spangles, grains or powder The silver is wogni/,ed by its color and by the fact that its solution in nitric acid yields a white precipitate upon the addition of a drop or two of hydro- chloric acid Copper and gold have nearly the same color, but copper dissolves in at id while gold is insoluble. Addition of an excess of ammonia to the solution of copper gives a char- acteristic, deep blue color
Iron, nickel, and cobalt give gray infusible powders winch are mag- netic, but yield no sublimates,
Molybdenum, tungsten, and some of the rarer metals give gray powders that are nonmagnetic and no sublimates.
Antimony yields copious white fumes, forming a volatile white sub- limate (Sb203), which becomes black when touched with the R.F.
1 Potassium cyanide must always be used with care, as it is a deadly poison, even in minute quantities
Blowpipe Analysis 475
When touched by the tip of the 0 F , it will volatilize and color the flame >cllowi&h green The metallic bead, when dropped upon a sheet of glared papci, breaks into a number of smaller ones
Arsenic volatilizes completely and consequently yields no globule of metal It gives abundant white fumes which form a white subli- mate and have a garlic odor The flame at the same time is colored blue
Bismuth yields a reddish white, brittle globule and an orange-yellow sublimate which becomes lemon-yellow when cold
Cadmium gives brown fumes in the 0 F and yields a reddish brown sublimate, while the flame is colored dark green
Lead yields a gray malleable bead, and incrusts the charcoal with a lemon-yellow sublimate near the assay The flame at the same time is colored blue The yellow incrustation is composed of lead oxide
Molybdenum gives a crystalline incrustation which js yellow when hot and white when cold When touched by the 0 F it becomes dark blue, and when heated for a longer time dark copper-red The blue incrustation may be molybdenum molybdate (MoMo04) and the red one, molybdenum dioxide (MoOJ
Selenium yields brown fumes, but the sublimate wfoch is near the assay is gray When heated with the reducing flame, it disappears and the characteristic bad odor is evolved The flame becomes blue
Tellurium coats the charcoal with a white sublimate bordered by dark yellow The coating disappears in the R F , which acquires a green color
Tin gives a white globule which is malleable and a yellowish white coating, turning white upon cooling When moistened with a drop of Co(N03)2 solution and heated in the OF, its color changes to blue-green
Zinc burns in the 0 F with a bluish white color and evolves thick white fumes which condense as a yellowish sublimate This be- comes white on cooling, and, when moistened with a dirop of cobalt nitrate and again heated, it turns grass-green (compare tin)
Other metals also give characteristic reactions on charcoal, but the above are the most important
DKTKRMINATIVK MINKHAUXrt
Use of the Beads.— The beads me used foi the deled ion of metals that produce tluiract eristic, coloied compounds when lusecl borax or microcosmic salt or some olhei leaent A pieie of pint mum wire fused mto a glass rod serves as a support. The end of the \vne is bent into a little loop This is moistened and plunged into powcleiecl borax, microcosmic salt or other reagent and then heated carefully until the adJhermg material is fused to a clear glass New material is added by dipping the loop again and again into the po\\dercd will and heating until the globules of glass are large enough to fill it completely. A tiny portion of the material to be tested is taken up by heating the bead and pressing it while still soft upon a bit of the powdered assay, which has been placed in a clean watch-glass. The bead containing the substance is then heated with the O.F. and afterward with the R.F , and the phe- nomena resulting are carefully observed If the reduction is difficult, a little stannous oxide or chloride will hasten it If the head becomes opaque because saturated with the assay, n portion is jeiked olT while it is hot and it is built up again by the addition of more of the teugent
In some cases, compounds other than the oxides do not yield the characteristic beads of the metallic oxides Therefoie, it is safer in all cases when testing by the bead reaction, to first toast the subslamc by gently heating on charcoal with the O.F. to chive off its volatile constit- uents
The colors of the most characteristic beads of metallic* oxides are tabulated below.
COLORS OP tiORAJC BEADS
Oxidizing Plamp,
KMUUIN Hot
Hot
Cold
Yellow or red Blue Green
Grass-green Blue
Chromium Cobalt Copper
Grown Ittuo Colorless
Colorless Yellow or red
Colorless Colorless or
Didyiruum Iron
ROM Bottle-green
yellow
Violet i
Reddish violet
Manganese
Colorless
Yellow or red
Colorless to
Molybdenum
Brown
Violet Colorless Colorless or yel- low
Reddish brown Colorless Colorless
Nickel Cdumbium TUtanium
Gray
Calprleiut nr nty Yellow or brown
Colorless or yel- low
Colorless
Tungsten
Yellow
Yellow or red
Colorless or yel- low
Uranium
Pale Kraun
Yellow
Green-yellow, or
Vanadium
Bruwniiih Krt'cn
nearly colorless
Kmeruitl-ttreen
ftltitt
Kttiltlish brown,
Rt
I'nlu bottle-gruen
Cnlfir1i*m Opaque brown
Oray
('ftlorlesH nr gray
Yellow nr brown
Yellow brown
le KW
Blowpipe Analysis
Colors Op Microcosmic Salt Br\Ds
OXIDI/INl Fl VM1
Reducing Flame
not
Cold
Hot
Cold
Reddish green Blue
Emerald-green Blue
Chromium Cobalt
Reddish green Blue
Emerald-green Blue
Crreen
Blue
Copper
Dirty green
Green, or opaque
red
Colorless
t ulorless
Didymium
Colorless
Blue
Yellow or red
Colorless, yellow
Iron
Yellow or red
Nearly colorless
or brown
Violet
Violet
Manganese
Colorless
Colorless
Green
Faint yellowish
Molybdenum
Dirty green
Green
Reddish to brown
Yellowish to red-
Nickel
Reddish
Yellowish to red-
dish
dish yellow
Colorless
Colorless
Columbium
Blue or brown
Blue or brown
Skeleton
Skeleton
Silica
Skeleton
Skeleton
Colorless
Colorless
Titanium
Yellow
Violet
Colorless Yellow
Colorless Yellow-green
Tungsten Uranium
Dirty green-blue Dirty gretn
Blue Bright green
lo colorless
Dark yellow
Light yellow to
Vanadium
Brownish green
Emerald-green
colorless
Cobalt is the only metal which produces the same colored bead under all conditions This is a beautiful blue Other oxides give blue beads under some one or more conditions, but under other conditions their beads have other colors
The cold bead of chromium oxide is always green and the oxidized bead of manganese is always violet
Flame Coloration.— Many substances impart a distinct color to the nonluminous flame of the burner or the blowpipe Frequently, these colors are best seen after the substance in powdered form has been moistened with hydrochloric acid, as the chlorides are usually more volatile than other compounds In the case of silicates, it is often ad- visable to mix the powdered assay with an equal volume of powdered gypsum In testing for flame coloration a very small particle of the substance, or its moistened powder, or of the mixture of the substance and gypsum is held in the flame by the aid of the platinum loop which has been cleaned by dipping into HC1, and heated repeatedly until it no longer colors the flame
When several different flame-coloring elements are present in the assay, the stronger color may mask the fainter one, and, therefore, some means must be made use of to shut off the brighter color, while allowing the fainter one to persist This is usually accomplished by viewing the flame through some medium (a screen) that is transparent to the faint rays and opaque to the brighter ones In other cases, two flames which are really different in color appear of nearly the same tint to the unaided eye. In this case, the screen is again used to cut off certain
478 Determinative Minkkalckjv
rays that arc common to the two colors, \vhen the remaining rays may be different enough to ho distinguishable The si icons most frequently used for this purpose are pieces of <oloied #lass, whith uic held close to the eye Red glass absoibs all but ted ui>s Blue tflass stops certain red and green rays and all the yellow ones Gicut difficulty is some- times experienced in securing glass exhibiting pure tolois, so that in most cases it is more convenient to use transparent celluloid films that have been manufactured expressly for the examination of colatcd flames These films are given the tints that are most useful for the purpose desired Care must be taken in using them, however, since celluloid is highly inflammable
For more accurate work the spectroscope is often employed. The use of this instrument depends upon the fact that each substance, when in the form of gas, emits light composed of one or mote lays of definite wavelengths, and the spectroscope separates these so that each may be identified. The most convenient instrument for blowpipe work is the Browning direct vision pocket spectioscope, but sime the con- stituents of all common minerals can be recogni/cd without the aid of the spectroscope there is no need for further rcfeiente to it,
The most characteristic colors imparted to the blowpipe flame are
Red by lithium, strontium, and calcium. Sodium salts obscure the lithium flame and banum salts the strontium and ralnum flames
Ydlow by sodium.
Green by most copper compounds, thallium, barium, antimony, phosphoric acid, bone acid, molybdic acid, and nitm and. The flame of phosphoric acid is bluish green, the flames of boric uud and barium are yellow KIWII, and those of molybdic acid and antimony are very faint. The copper and thallium flames are vivid greens* The nitric acid flame coloration is bron/e green ami exists as a flash only
Blue by copper chloride, copper bromide, selenium, arsenic and lead The arsenic flame is faint. Tht selenium and the copper chloride Humes arc brilliant azure-blue
Violet by potassium, caesium and rubidium. Sodium and lithium salts obscure the reaction
Detection of Certain Elements in the Presence of Others,— In many cases, as has been stated, the color imparted to the flume by one substance entirely obscures that given it by another when the two are present in the same compound. Thus, the faint violet color of the potassium flame is obscured by the strong yellow of sodium and the brilliant red of lithium. When this is the case, the light is viewed through the proper screens and the different rays in this manner are
Blowpipe Analysis 479
differentiated Since the flame tests afford the readiest means of detect- ing the alkalies and alkaline earths, considerable attention has been devoted to means of differentiating their flame colors Among the methods proposed for this purpose is that based upon the use of blue and green glass screens
Detection of the Alkalies and the Alkaline Earths.-— The potas- sium flame is reddish violet through blue glass, while the sodium flame is invisible or is blue, hence, the potassium flame is detected in the pres- ence of sodium by viewing the mixed flame through a blue scieen Lithium is also detected m the presence of sodium with the aid of blue glass, since the lithium flame is violet-red when viewed through a blue screen Since the flame colors of Li and K are so nearly alike when viewed through a blue screen, they cannot easily be distinguished When viewed through a green screen, however, the Li flame is nearly invisible, while that of K is bluish green Through the green screen the Na flame appears orange
If search is to be made for the alkaline earths, the assay is repeatedly moistened with sulphuric acid and placed in the hottest portion of the flarne After the alkalies are driven off, the flame will become yellowish green, if barium is present, through green glass it will appear bluish green The assay is then repeatedly moistened with pure hydrochloric acid and again brought, while still moist, into the hottest portion of the flame A red coloration, appearing after the yellowish green barium flame has disappeared, indicates calcium or strontium or both Through green glass the calcium flame appears green and the strontium flarne faint yellow foi an instant Through blue glass calcium gives a faint greenish gray and strontium a puiplc or rose color
The phenomena exhibited by the alkalies and alkaline earths may be summarized as follows*
Flame Color Through Blue GKiss Through Green Glass
Potassium Violet Reddish violet Bluish green
Sodium Yellow Blue to invisible Orange-yellow
Lithium Carmine Violet-red Invisible
Barmm Yellow-green Bluish green
Calcium Yellow-red Green-gray Green
Strontium Scarlet Purple Faint yellow
The detection of the alkalies m silicates is accomplished by fusing the powdered assay on platinum wire with a little pure gypsum If the alkaline earths are sought for, the assay is fused with sodium carbonate on platinum wire, or better, on a piece of platinum foil The fused mass
480 Determinative Miner Aiakjy
is then extracted with water ancl the lesiclue tieated with hychochlonc acid Silica will be precipitated, leaving in the solution a mixture of sodium chlonde and the chloiules ol the alkaline eailhs The solu- tion is then tested m the flame the aid oi a clean ])latimim wire
The Copper Test— An almost certain test lorcoppei and loi chlorine is affoidcd by the difference in the coloi imparted to the llame by copper chlonde and most other coppei salt** Seveiul substant es beside*; copper give green flames, but in the case ol eoppei alone the colot oi the flame is changed to sky blue by touching the assay with IH1, 01 a chlonde.
Special Tests. — A fe\v tests with special reagents are so charac- teristic for certain elements that they are specific:
Tests with NasCO.j.— (i) When a powclcied substance containing S is fused with four times its volume oi dry Na.CO,i and heated intensely for some time on charcoal, the residue1, when placed on a silvei com and moistened with water or hyclrochlouc acid, will yield a black or brown stain. This reaction is due to the production of N<iiS(BuSOt f NaaCOs +C23=Nti2S+BaCO,i+2C02), which is soluble, The solution containing the sulphide reacts with the silver, producing insoluble At&S, which is brown or black Thus: NaaS+Aft,+HjO+OAftsS+2NaOIL Sul- phides and sulphates are distinguished by roasting the compound on chaicoal without NasCO.j Sulphides yield the sulphur-dio\ide odor,
(2) Manganic and (hiomutm tompounds, fused with N;ii>C04j (especially when a little niter is added), vield lolorvd masses -the manganese compound a l> green mass (NagMnOt) and the chro- mium compounds a bright yellow mass (NtigCrOt). In the case of the manganate, the reaction may be
MnQj+NaaCQa+O-NaaMnOt+COa.
(3) Sodium carbonate may also be emi>loyed for tfaiHHfasittg iffiiatn and detecting silicic Acids If a silicate is fused with 4 or 5 times its volume of Na2COa on charcoal, it will break up, the silica combining with soda to form sodium silicate, thus:
(ZnOH)2Si03+ aNasCOjj - aZnO+No4SiOi+ 2CO*+ Hs0,
Upon treatment with acid, H4Si04 is produced (Ntt4S!Oi4-4HCI 4NaCi +H4Si04). This appears as a gelatinous precipitate in the solution; but upon evaporating to dryness, moistening with strong acid, and again evaporating to dryness, the H4SiOt is broken down into 2HS0 and SiQa, the latter of which is insoluble, and can be filtered off, leaving the bases in the filtrate
Tests with the Cobalt Solutions—Certain metallic oxides, when
Blowpipe Analysis 481
moistened with a few drops of a solution of crystallized cobalt nitrate dissolved in ten parts of water, and heated, yield distinctive colors that may often serve as aids in their detection The assay is powdered, moistened with a drop of the cobalt solution, and placed on charcoal and heated intensely Compounds containing alumina yield a mass of a blue color, without luster A few other substances may also give blue masses, but the materials are fused and, consequently, show a glassy luster Magnesium compounds give a pink color
In testing for other substances, it is necessary first to obtain their oxides This is done by roasting on charcoal until a distinct subli- mate is produced This sublimate is moistened with a drop of the solution and heated gently by the 0 F Under these conditions, the white zinc sublimate (ZnO) changes to a bright yellowish green and tin oxide (SnCte) to a bluish green
Tests with Acid Potassium Sulphate.— Hydrogen potassium sul- phate (HKS04) when fused with a powdered substance in a closed tube, may cause the evolution of gases For example
2HKS04+CaF2 K2S04+CaSC>4+2HF,
which in many cases may easily be recognized
Nitrites and nitrates yield reddish brown fumes (N.A) with the character- istic odor of nitiogcn peroxide
Chhi ales yield a yellowish green explosive gas (CIO..)
Iodides yield a violet gab, which colors blue a papei soaked m starch paste, when a little MnOa ib added to the HKS04
Bromides yield a reddish blown gab (Br), turning staich paste yellow, when MnOj is mixed with the HKSd
Chlorides yield hydrochloric acid (HC1), recognized by its odor and the voluminous white fumeb it forms with ammonia
Sulphides yield hydrogen sulphide (HjS) with itb characteristic odor This gas blackens paper moistened with lead acetate
Fluondes yield hydroiluonc acid (III) gab, which has a pungent odor and etches glass The etching is due to the reaction between the SiOj of the glass and the HF Thus, Si02+4HF=SiF4+2H.0 The SiF4 is volatile and is duven up the tube, leaving tiny pitb from which the SiOj was taken This reaction is best seen by heating the assay with four times its volume of the reagent and then cleaning and drying the tube
The reaction is more delicate if the finely powdered assay is mixed with microcosmic salt and heated m an open tube "When the salt is heated, it breaks up, yielding NaPO, (thus HNii(NH4)P04 4H20=NaP03+NHJ+sH80) which reacts with the fluoride as follows
CaNaP04+2HF
482 Determinative Mineralogy
By Reduction with Metallic Zinc and Hydrochloric Acid certain metallic salts yield colored solutions which sire characteristic. The substance to be tested (if not soluble in IIC1) is powdered and mixed thoroughly with sodium caibonate and nitci, and the muss is slightly moistened and placed m a htlle sphal at the end of a line platinum wire After fusion, it is dissolved in a little water, a lew chops of hydrochloric acid are added and a strip of zinc or tin, or a few Bruins of the metal, are then placed m the solution The hydiogen, evolved by the contact of the metal and the acid, i educes the oxides and the solution becomes colored The most important elements detectable by this method are:
Molybdenum, which gives a blue, then guvn, and itiully a blackish brown solution
Tungsten, a blue, then hi own or copper-red solution
Vanadium, a blue, green or vjolet solution,
Columbum, a blue solution which loses its color on addition of water,
Chromium, a green bolution
Titanium, a violet solution.
In the case of titanium the read ions are,
TiO,+aN.ij(U--N,uTi04 .' Na<Ti04+8Hn " TK'U 1 .|Na('l TiCliiH TiClitHt'l.
The TiCfo produces the violet solution.
Magnesium ribbon is geneiully employed us an aid in the detection of phosphoius The powdered assay is placed in the bottom of a closed glass tube with a piece of magnesium ribbon about 5 mm long, so that the powder is in close contact with the metal. This ts then heated in- tensely until partial fusion ensues. The completion of the reaction is known by the formation of a brown or black glass, winch is the phos- phide of magnesium. Upon crushing the tube and moistening its con- tents with water the characteristic odor of phosphine is perceived (the odor of wet phosphorus matches),
Hydrochloric acid furnishes the readiest test for carbonates. If the powdered substance is heated gently with dilute acid in a test tube, a brisk effervescence will result if it contains the carbonic arid radical. Sometimes the effervescence can be detected by holding the mouth of the test tube to the ear, even when the escape of gas cannot be seen. The gas (COg) is colorless, and when allowed to bubble through lime water will cause turbidity,
Chapter Xxiii
CHARACTERISTIC REVCTIONS OF THE MORE IMPORTANT ELEMENTS AND ACID RADICALS
Aluminium (p 481) —Fusible minerals cannot be satisfactorily tested for Al by the method using CXNOata since cobalt imparts a blue color to all glasses
Since zinc silicates yield the same color reaction with Co(NOs)2 as do infusible aluminium compounds, the presence of aluminium in silicates cannot be assured unless the absence of zinc is proven
Antimony (pp 472, 473, 474, 478) —In the presence of lead or bis- muth, the assay is heated on charcoal with fused bone acid, which dis- solves the lead and bismuth oxides, while the antimony oxide coats the charcoal
When antimony and lead are piesent in the same compound, the anti- mony oxide forms a white incrustation surrounding a dark orange-yellow incrustation of lead antimonate
Arsenic (pp. 472, 473, 475, 478) .—Arsenic in arsenates and arsen- ites may usually be detected by heating the powdcied assay with six times its volume of a mixture of equal parts of NasCOs and KCN (or powdered charcoal) in a dry closed glass tube, when an arsenic mirror will form on the cold part of the tube This may be further tested by breaking off the end of the tube and heating the mirror in the burner flame The escaping fumes will have the characteristic garlic odor. If allowed to pass through the flame, they will tinge it violet.
If there is doubt as to whether a white sublimate on charcoal con- tains arsenic, or if it is desired to test for arsenic in the presence of anti- mony, a little of the coating which is farthest away from the assay may be scraped from the surface of the charcoal and placed in a narrow glass tube and heated If arsenic oxide is present in the coating, the arsenic mirror will form on the walls of the cooler part of the tube.
Barium (pp 478, 479) .—Before applying the flame test for barium, silicates should first be fused with four parts of dry Na2COa and charcoal in a loop of platinum wire, crushed, placed in a test tube, treated with a
484: Determinative Minichalocsy
few cc of dilute UNO* and cvapoiatccl to dryness After c ooling, warm with a very little HC1, then add about to cc of \\alci and lilter off the insoluble silica. To the filtrate add a few drops of IfeSOj, collect the precipitate on a small filter, and test with the flame (see also under Calcium).
Bismuth (pp 472, 475) — A veiy chainttcnstic test is the following: The powdered substance is mixed with twice its volume of a mixture composed of equal parts* of KI and floweis of sulphui, iind heated in the RF on charcoal If Bi us present, a blick-red iodide of bismuth will form a coating at some little distance from the assay. This test serves to distinguish between Pb and Hi, both of which yield yellow oxide coatings when tested on charcoal
Boron (p 478) —To obtain the green flame in the rase of most com- pounds containing boron, it is usually sufficient to moisten the line pow- der with a drop of strong sulphuric acid and introduce a small quantity into the flame on a platinum wire The flame will be colored green, but only for a moment. More resistant compounds, like the silicates, must be fused with a flux; composed of one jKirt of powdered fluonqxir and four parts of KHSOt before the green coloration can be obtained. The HF generated decomposes the silicate and sets free the boron.
In the presence of copper compounds or phosphates, which also give green flames, the finely powdered assay is moistened on platinum foil with sulphuric acid. The excess of acid is then removed by heating, and the powder mixed into a paste with glycerine and a little sodium car- bonate When heated in the flame, the sodium will mask t he green color due to the copper and phosphorus, but not thai produced by boron.
If boron compounds are fused with Nua("Q and then treated with dilute HC1, a drop of the resulting solution will cause turmeric paper to turn reddish brown after being dried at ioo° If moistened with am- monia, the color changes to black.
Bromine (pp. 478, 481) —Solutions of bromides in water or HNQt (after fusion with NasCOa if insoluble otherwise) will yield with a drop or two of silver nitrate solution a yellowish precipitate of AgHr, which is soluble in ammonia If this precipitate is mixed with Iii*S and heated in a dosed tube, a yellowish sublimate of BiBr& will result, (Compare Chlorine and Iodine.)
Cadmium (pp. 475, 478).— When present with Pb or Zn, it is often difficult to recognize the cadmium coating on charcoal, In this case, the
Characteristic Reactions, Etc 485
coating may be scraped from the coal and heated very gently in the closed tube A yellow sublimate of cadmium oxide will form just above the assay On further heating, this will be masked by the zinc and lead oxides
Calcium (pp 478, 479) — Calcium in silicates and other insoluble compounds may be detected by the same method as that used for the detection of barium The precipitate of CaSO*, however, is dissolved when heated with a large volume of water
Carbonates.— See p 482
Chlorine (pp 480, 481) —Chloride solutions, when treated with AgNOs, yield a white precipitate of AgCl, soluble m ammonia When exposed to the light, it darkens If mixed with 61283 and heated m a closed tube, a white sublimate of Bids is formed (Compare Bromine and Iodine )
Chromium (pp 476, 477, 480, 482) — In the presence of large quantities of Fe, Cu, etc , the powdeied assay (if not a silicate) is mixed with double its volume of equal parts of Nd2COs and KNOs and fused on a platinum spiral m the 0 F , when an alkaline chromate will be foimed This, dissolved in water and boiled with an excess of acetic acid yields a solution which gives a yellow precipitate of PbCr04 with a few drops of lead acetate
Silicates containing small quantities of chromium and large quanti- ties of copper and iron should first be fused on charcoal with a mixture of one part of sodium carbonate and a half part of borax The clear glass thus produced is dissolved in hydrochloric acid and the solution evaporated to dryness This is then treated with water, filtered, and the filtrate boiled with a few drops of nitric acid to oxidize the iron By the addition of ammonia, the chromic and other oxides are precipitated The precipitate is collected on a filter, washed, and treated as above, or tested with the bora\ bead
Cobalt (pp 474, 476, 477) —For the detection of cobalt in the pres- ence of iron or nickel, see under those metals
Columbium (pp 476, 477, 482) —When a compound containing columbmm is fused with five parts of borax on platinum foil, dissolved in concentrated HC1 and diluted with a little water, the solution be- comes blue when boiled with granulated tin. The color does not change to brown on continued boiling It disappears, however, when diluted with water. If titanium is present in the same solution the
486 Detkrminativk Minmualo(!Y
color will be first violet, then blue Tungsten, gixes a blue solu- tion under the same conditions, can be distinguished fiom t olumbwm by the bead test If the solution is boiled \\itli xu, instead ot tin, its coloi changes rapiclh from blue to bro\\n
Or the finely powdered substance may be lused in a test tube or crucible with ten paits KITSOi, and then digested cold \\atcr for a long time If columbium is present, an insoluble \\hilo lesidue will he left This, if collected on a filter, washed, and then treated in n test tube with hot concentrated HOI, will yield the blue solution boiled with granulated tin,
Copper (pp 474, 476, 477, 478, 480") veiv deluate test foi soluble coppci compounds is to dissolve them in HCI 01 IINOa, dilute with water and add ammonia m CM ess A deep pimple-blue solution of CuCl2'6NH3 or Cu(NQa),j 6NH,, will lesult
Fluonne (pp. 472, 481) -If the mineinl to be tested is a silicate, its powder ib mixed with four parts of fused mil MXOMIW salt and this mix- ture is heated in a closed tube If fluorine is piesent , t he glass above the assay will be etched by the HF produced At the same time, a ling of SiOg is deposited in the cool portion of the tube in consequent e of the reaction
allaSiFn r SiOa
Upon heating, the ring moveb up the tube to a tooler portion,
Gold (p 474).— The metal is best detected bv Ueatment with aquaregia of the metallic bead, produced by fusion with NaaC%(),j on charcoal This yidds a light yellow solution, which, when taken up on a filter paper and moistened with stamuws chloride, gives tin* " purple of Cassius,"
Or, if the mineral is to be tested for free gold, it is powdered and treated with aqua regia and the solution diluted and filtered The fil- trate is evaporated nearly to dryness, diluted with water urn! a few drops of a solution of ferrous sulphate are added. If gold is present in small quantity only, the solution will be colored bluish or purple, If the #old is present m larger quantity, the metal will be precipitated us u brown powder.
Free gold may also be detected by powdering the substance until all will pass through a fine sieve. Brush the material adhering to t lie sieve and add to the powder. Then place in a basin containing a lit lie mer- cury (i cc), and immerse the basin and its content in water, Shake the basin gently with a rocking motion and gradually allow the rock
Characteristic Reactions, Etc 487
powder to escape The gold will fall to the bottom and amalgamate with the mercury After the mass has been reduced to a small volume, transfer to a mortar and grind in a gentle stream of water, until nothing but the amalgam is left Then place in an iron spoon and heat in the open air until all the mercury is driven off, or the amalgam may be placed in a shallow cavity on charcoal and heated with a small blowpipe flame until all the mercury volatilizes The residual gold may be col- lected into a globule by placing a little borax or sodium carbonate m the cavity and heating until quiet fusion takes place
When off the mercury from the amalgam extreme care must be taken not to bieathe its fumes, since they are poisonous. The operation should not be performed in a closed room
Iodine (p 481) — Substances containing iodine, when fused in a glass tube with KHS04 and Mn02, yield a vapor which is recognized as that of iodine by its violet color
In the presence of other halogens, iodine may be detected by mixing the powdered substance with 81383 (prepared by fusing together small quantities of bismuth and sulphur) and heating in a closed tube or on charcoal before the blowpipe. If iodine is present, a red sublimate of bismuth iodide is produced (Compare Chlorine and Bromine )
Iron (pp 472, 474, 476, 477) — To distinguish ferrous and ferric conditions, the assay is added to a borax bead containing copper If the iron is in the ferric condition, the bead will be bluish green, if in the ferrous condition, it will contain red streaks of cuprous oxide.
In the presence of easily fusible metals like lead, tin, zinc, etc , the substance is heated on charcoal with borax m the R F The easily reducible metals do not become oxidized and, consequently, are not absorbed by the glass The glass is separated from the metallic bead, and is heated on a fresh piece of charcoal in the R F , when it acquires the characteristic bottle-green color produced by iron, and becomes vitriol-green on addition of tin
In the presence of cobalt, the blue color of the cobalt bead masks the green of the iron bead In this case, iron is detected by heating the blue glass on platinum wire m the 0 F. sufficiently long to convert all the iron into peroxide. With very little iron present, the bead is green when hot, and blue when cold, with more iron the bead is dark green when hot, and pure green when cold, this latter color resulting from a mixture of the yellow iron and the blue cobalt colors
Manganese colors the borax bead in the 0 F red Upon reduction with tin on charcoal, the bead becomes bottle-green, If cobalt also is
488 Determinative Mineralogy
present, the bead produced in the 0 F is Auk violet Tu the R F it becomes green when hot and blue when cold
Lead (pp 472, 475, 478,) —-The coating of lead oxide icsemblcs very closely that of bismuth The two may be distinguished by the pro- cedure descnbed under bismuth The iodide of lead is lemon-yellow.
Lithium (pp 478, 479) — In the case of silicates, beioio testing for flame coloration, it is advisable to mi\ the powdci of the assay with one part of fluorspar and one and a half parts of KHSOi and foi m into a paste with a drop of water If boron is present, the flame is at lust green, then red The presence of phosphoric acid is shown by the production of a green flame together with the red one This ib especially noticeable after moistening the assay with sulphuric acid
Magnesium (p 481) —The Co(NOs)2 test for magnesium is applica- ble only to white or colorless minerals ancl is by no means conclusive. The most satisfactory test is that employed generally in oidmary quali- tative analysis, viz, precipitation with the aid of sodium phosphate* The powdered mineral, if soluble in acids, is fused with powdered, dissolved in a few cc of dilute HNO and evapo- rated to dryness It is then dissolved m 2 or 3 cc, HC1 and warmed for a few minutes There is next added about 10 cc, of water and the solu- tion is boiled and filtered to remove silica. The filtrate is heated to boiling and NEUOH is added m slight excess to pi capitate iron and aluminium. This is now filtered and the filtrate is boiled again, and to it is added some ammonium oxalate ((NHCoO*) to separate calcium. After ten or fifteen minutes, the calcium oxalate is removed by several nitrations until the filtrate is clear To the filtrate a solution of sodium phosphate and strong ammonia are added. If magnesium is present after standing for some time, a fine white crystalline precipitate of NH4MgP04 6H20 will form
Manganese (pp. 477, 480) —Manganese compounds soluble in HNOs are readily detected by oxidation with persulphate*. The pro- cedure is to dissolve in a few cc of moderately dilute HNCXj (sp. gr i 2), add about one-half its volume of dilute solution of AgNOa ancl a few drops of ammonium persulphate (200 gr (NHOaSsO* to one liter of water) and gently heat The manganese will be oxidized to perman- ganic acid, which is purple The reaction is
Characteristic Reactions, Etc 489
Compounds that are insoluble in HNOs must first be fused with Na2COs on charcoal
Mercury (pp 472, 473) — In the presence of sulphur, chlorine, iodine and a few acids, the assay is best heated with dry Na2COs in a closed glass tube The acid combines with the Na and the Hg sublimes.
Molybdenum (pp 474, 475, 477, 478, 482) —The white coating of MoOa on charcoal, if touched with the R F , is partly reduced, be- coming blue If heated by the 0 F , some of it volatilizes, but some is reduced by the charcoal, forming a copper-red coating
Small quantities of molybdenum are detected by treating the pow- dered assay with a little strong sulphuric acid on a platinum foil After heating until most of the acid is evapoiated, and then cooling, the result- ing mass becomes blue, particularly after being repeatedly breathed upon, or after being moistened with alcohol and dried by heating
Nickel (pp 474,476,477) —In the presence of Co, the color of the Ni borax bead is often masked In such cases, a small portion of the mineral is fused in the R F to a globule A fragment of borax " twice the size of the globule is placed beside it on charcoal and the two are heated by the 0 F The two globules will roll around under the flame in contact, but will remain quite distinct, any cobalt will be oxidized by the 0 F and be absorbed by the borax, which will become blue If the mineral is placed upon a clean part of the coal and the treatment is continued with fresh portions of borax until all the cobalt has been oxidized and the borax no longer becomes blue, the nickel present will impart its characteristic violet and reddish brown color to the borax " (Phillips )
Nickel is best detected by ti eat mg its solution with dimethyl gly- oxime ((CHj)oC2(NOH)o) The assay is dissolved in acid, after fusion with Na2CO<3, if necessary, and the solution i& neutralized with (NEWQH Add one-half volume of dimethyl glyoxime solution, made by dissolving one part of the compound in 100 pts of a 40 per cent alcohol, and again add a little (NHOOH to neutralize A bright red crystalline precipitate will form if nickel is present, according to the leaction.
NiCl2+2(CH3)2C2(NOH)2 - (CH3)2C2(NOH)2 (CH3)2C2(NO)2Ni+2Ha
Hitnc Acid (pp. 472, 478, 481).— Nitric acid is best detected by dis- solving the assay in dilute (i : i) BkSO-i, cooling and adding to the solu- tion in a test tube a few drops of a strong solution of FeSO* in water,
490 Determinative Mineralogy
holding the tube slanting and allowing the FeSC>4 to trickle quietly down its side and form a layer upon the acid solution If nitrates are present, a brown ring will form at the contact of the two solutions
Oxygen, in some of the higher oxides, may be detected by the liber- ation of chlorine when they are treated \sith HC1 This is particularly the case with the higher oxides of manganese, thus
Mn02+4HCl-MnCl2+2H20+2CL
The chlorine is recognized by its color, its odor and its bleaching action
Phosphoric Acid (pp 478, 482) —In the test with magnesium ribbon, it is best to fuse the phosphates of Al and the heavy metals with two parts of Na2COs on charcoal, to remove and grind the fused mass, and then to ignite the powder with magnesium ribbon in a closed glass tube (Brush and Penfield)
If a small crystal of ammonium molybclatc (NHOMoOi be placed on a phosphate and a little dilute HNOu be dropped upon it, the crystal will turn yellow in consequence of the production of ammonium phos- phomolybdate ii(Mo03) (NH4)3P04 6H20 This test is available only for compounds that are soluble m HNOs
If the mineral is insoluble m HNOa, it must first be fused with sodium carbonate on platinum wire The bead is then dissolved in nitric acid and the solution when cold is added drop by drop to a little of an ammo- mum molybdate solution and allowed to stand without warming. If the assay contained the phosphoric acid radical, a yellow phospho* molybdate will be formed.
Potassium. — See pp 478 and 479
Selenium (pp 473,475,478) — Selenates and sclemtes must be reduced with sodium carbonate on charcoal before the peculiar otlor is evolved.
Silicon (pp 477, 480) —Small splinters of silicates yield an infusible skeleton of silica when heated in a bead of microcosmic salt. This flouts around m the liquid bead as a particle with the shape of the original splinter, or as a transparent flake In some cases the original splinter remains undecomposed
Many silicates decompose in strong HN04 or HC1 with the produc- tion of a gelatinous mass of silicic acid If the solution containing the gelatinous silica is evaporated to dryness, the silica becomes insoluble
Characteristic Reactions, Etc 491
and remains as a residue when the mass is warmed with a little strong acid and digested with water
In case of insoluble silicates it is necessary to fuse with Na2COs before proceeding with the test The fusion results in the production of a sodium silicate which is soluble in acids The gelatinous precip- itate will appear only after the acid solution of the fused mass is evap- orated
Silver.— Seep 474
Sodium — Seepp 478 and 479
Strontium (pp 478, 479) — In the case of insoluble compounds treat as in the test for Ba If both Ba and Sr are present in the final pie- cipitate, the flame will first be crimson Upon repeated moistening with HC1 and heating, the Si will gradually disappeai and the green color of the Ba flame will be seen
Sulphur (pp 472, 473, 480, 481) — If a substance containing sulphur is heated with NaoCOs on charcoal in the R F and the fused mass is transferred to a watch glass and moistened with water, the addition a little dilute solution of ammonium molybdatc, to which HC1 has been added, will pioduce a blue color
Sulphides arc distinguished fiom most sulphates (except those con- taining water or the OH group) by heating in the 0 F The sulphides yield an odoi of SOj The sulphates yield no odor Anothci means of distinguishing between these two classes of compounds is as follows The finely powdcied substance is fused with caustic potash (KOH) in a platinum spoon, or on a piece of platinum foil The spoon or foil with its contents is thrown into water containing a strip of silvei If the silver remains quite white, the S is present as sulphate, if the silver becomes black, S is piesent as sulphide Substances exercising a reduc- ing action must, of course, not be present
Tantalum cannot be recognized in the presence of columbium by any simple tests
Tellurium (pp 473, 475).— A powdeied tellurium compound, heated with Na2COs and charcoal powder in a closed glass tube and treated when cold with hot water, yields a purple red solution of sodium tel- lunde This color will disappear if air LS blown through the solution.
Tellundes may be detected by gently warming the finely powdered substances with a few cc of concentrated sulphuric acid The solution
492 Determinative Mineralogy
will become carmine After cooling, the addition of water will piecip- itate the tellurium as a blackish gray powdei, and the carmine color will disappear
Thallium. — Seep 478
Tin (pp 475, 4x) — The reduction of tin compounds is accomplished fairly easily by mixing borax with Na2COj and ttcatincj the K F on charcoal The metallic tin thus obtained, when heated on charcoal by the OF, yields a white incrustation which becomes bluish green when moistened with cobalt nitrate and heated (see Znu) Or, if warmed in a test tube with moderately dilute HNO*, a white powdery metastannic acid (EfeSnOs) will result
If to a borax bead colored blue by a copper, a small quantity of tin compound be added and the RF be applied, the bead will turn brown
Titanium (pp 476, 477, 482) — If iron is piesent, the bead of micro- cosmic salt in the 0 F has the iron color, and in the R F a blood-red color. When this is fused with tin in the R.F. on charcoal, the color becomes violet
A very characteristic reaction is obtained as follows Fuse on char- coal or platinum foil one pa.it of the assay with ft paits oi NujCOj and a little bora\ Then dissolve m a small quantity of toncent rated HC1 (2-2 5 cc) and add granulated tin. The Imhogen genet a ted by the tin and HC1 will reduce the TiCh in the original acid solution to TiCla and the solution will assume a violet color, especially after standing several hours
For an extremely delicate test, fuse the powdered assay with Na2COs and borax, as m the color test with tin If the fused mass is dissolved by heating in a test tube with 2 cc of a mixture of equal parts of IlgSOi and water, and, after cooling, is diluted with about 10 cc of cold water, the addition of a few drops of HsOg to the diluted solution will produce a golden yellow or orange color if titanium is present.
Tungsten (pp 474, 476, 477, 482) —When present m small quanti- ties, tungsten may be detected by fusing the assay with five or six times its weight of Na2COa, extracting the resulting mass with water, filtering and adding to the filtrate strong hydrochloric acid. White tungstie hydroxide will be precipitated and this precipitate will become pale yellow (WOa) on boiling Upon acidification and boiling with a few particles of tin, a blue mixture of oxides results. The blue color will not
Characteristic Reactions, Etc 493
disappear on the addition of water (Compare tests for columbium ) On long-continued boiling, the color will change to brown (WOs)
If the tungstate be decomposed by boiling with HC1, it is not neces- sary to fuse Simply boil with strong acid until a light yellow precipi- tate (WOs) is obtained Then dilute with an equal quantity of water, add tin and boil, and the clue color will result. This will change to brown on long-continued boiling
Uranium (pp 476, 477,) — If the uianmm is so mixed with othci metals that its characteristic bead is obscured, dissolve the assay m HC1 (first fusing with Na2COs or borax, if necessary), then nearly neutralize ammonia and add a strong solution of Na2COs until precipita- tion ceases, then about half as much more and let stand for some time The excess of Na2CO.j will dissolve the compound first precipitated Filter, acidify the filtrate with HC1 and boil until all the COa is expelled Then add ammonia in excess If uranium is present, it will be precipi- tated as a gelatinous light yellow ammonium uranate (NH 1)211207 To confirm, filter and test the precipitate in the bead of microcosmic salt
Vanadium (pp 476, 477, 482) — Vanadium compounds, first roasted on charcoal and then fused with four parts Na2COs and two parts potas- sium nitrate on a platinum spiral, when extracted with hot watei, filtered, acidified with acetic acid, and treated with a few drops of lead acetate, yield a pale yellow precipitate of Pb,3(V04)a This may be tested for vanadium in a microcosnuc salt bead.
If the solution obtained by extracting the fused mass be filtered and acidified with HC1 and well shaken with hydrogen peroxide, it will become reddish brown or garnet color If to the acidified solution metallic zinc be added, a green blue color will result. This, however, will gradually become violet if the solution is left standing in contact with zmc
If the substance is soluble in concentrated HC1 or HfeSOt, the solu- tion thus produced will be red-brown On the addition of water the color will change to green-blue or will disappear Upon the addition of HaOa the i eddish brown color will reappear if the dilution be not too great If treated with metallic zinc the green blue color will again appear, but will gradually change to violet on continued action of the zinc If the blue or violet solution is poured off the zinc and a few drops of hydrogen peroxide be added, the characteristic brown color will again result For a more accurate determination of the presence of vanadium, add NHiOH in excess to the acxd solution and pass
494 Determinative Mineralogy
through it HsS The solution will become garnet if vanadium is present
Zinc (pp 472, 475, 48*) — Infusible white or light-colored zinc com- pounds, when finely powdered and made into a paste with a drop of Co(N03)2 solution, and then heated on charcoal by an O,F , assume a green color But silicates of zinc when treated m this way with a hot flame often form a fusible cobalt silicate which is blue
In the presence of antimony and tin, it is almost impossible to detect zinc by blowpipe tests, as all three metals exhibit nearly the same blowpipe reactions However, the zinc sublimate when moistened with Co(N03)a solution and heated in the OF. becomes grass-green, whereas the tin sublimate, under the same treatment, becomes blue- green
Zirconium, in the absence of titanium, molybdatcs and boric acid, may be detected, after fusion of the assay with a little NaaCO,j, by dis- solving the assay in a few drops of strong HC1 and diluting with water to four times the volume, and then moistening with this dilute solution a piece of turmeric paper When the paper is dried gently its color will change to reddish or orange if zirconium is present
Appendices L Guide To The Descriptions Of Minerals
BECAUSE of the great number of minerals known and the difficulty of recognizing them at sight, some means must be employed to aid in their systematic study in order that they may be identified without an inordinate expenditure of time The most convenient method of arriving at the name of a mineral is by means of a guide, or a set of tables similar in scope to the " keys " used in Botany for determining the names of plants, Many tables have been pioposed by mineralogists for this purpose and many different kinds are still in use Some of these are based on the chemical properties of minerals, and others on their physical properties. Both kinds possess advantages Those based on chemical properties are more effective in leading to the name of the mineral being studied, but those based on physical properties are more apt to lead to a better knowledge of its most evident charac- teristics
The most serious objection to the use of determinative tables lies in the danger that the student will feel, when the name of the mineral is obtained, that the object of his search is at an end, whereas their true aim should be to lead him to such a thorough study of the mineral that there will remain no doubt in his mind as to its real nature
In the present volume the tables are intended to serve simply as guides to the descriptions of the minerals given in the body of the text. It is here that the distinctions between the different species must be found In many instances the differentiation between several minerals is dependent upon chemical tests; hence it is desirable to familiarize oneself with the characteristic tests of the various metals and the acid radicals
The tables in the following pages are divided into two great divisions. The first division includes those minerals that have a metallic luster, and a few which might be confused with these Minerals possessing a metallic luster are opaque on their thinnest edges Most of them give a black or dark-colored streak. The second division includes the remain- ing minerals, i e , those with a nonmetalhc luster These are trans- parent in splinters and on their thin edges, and most of them give a
496 APPENDlUJkb
colorless or light-colored streak. The subdivisions are based on color of streak, color in reflected light and hardness With reference to hard- ness it is convenient to remember that minerals with a hardness of less than 2 5 will leave a mark on paper, those with a hardness of less than 3 5 can be scratched by a cent, those with a hardness of less than 6 can be scratched by a good knife blade, and those with a hardness of less than 7 can be scratched by quartz
In testing for hardness it is important to know not only that the scratching substance will actually scratch the substance being tested, but also that the latter will not scratch the former. Further, it is like- wise important that the scratching substance be clean and fresh. If a cent or a knife blade is being used for scratching, it should be bright; if a mineral is being used, it should not be coated with a Urmsh or a layer of weathered substance
It is also to be remembered that the color of a mineral is its color on a fresh fracture and not on a weathered surface.
Again, it must be stated that the tables in this book are not expected to determine for their users the names of minerals; they are to serve merely as guides to the pages on which the minerals are described. Recourse must be had to the descriptions of the individual minerals before the nature of the substance being studied can be established.
Appendices
Key To The Determination Of Minerals
A -Minerals With Metallic Luster '
Streak Black Or Dark Gray
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Ref ' Page
Lead
Arsenic
Tetradymite
Domeykite
White
Bismuthmite
White
Lollmgite
"3
or
Jamesomte
or
Cobaltite ,
Light Gray
Stibmte Calavente Galena
Light Gray
Smaltite Arsenopynte Chloanthite
nr loS
Clausthahte
Marcasite
Stromeyerite
Sperryhte
Calavente
Pentlandite
Brassy Bronze
Bormie Millente Domeykite
Brassy Bronze
Pyrrhotite Niccolite. . Pynte
3 5-4 5
Chalcopyrite
Marcasite
Molybdenite
Enargite
Graphite
Tetrahednte
Pyrolusite
Arsenic
Wad
Uramnite
Melaconite
Staurohte
Stibmte
Iron
Dark
Jamesomte
Dark
Wolframite
Gray or
Polybasite Pearceite
Gray or
Psilomelane Ilmenite
5H5
i8&
Black
Stephamte Argentite
Black
Magnetite Franklimte
5*5-6 5 5 5-6 5
i9a
Galena
Si
Pohamte ,
Chalcocite
Braumte.
Bournomte
Columbite ,
29$
Stromeyente
Tantahte, ,
6-6 $
Metacmna-
Corundum .
barite
Blue
Covelhte.
1 The ref
are to pages in this book
Appendices
A— MINERALS WITH METALLIC LUSTER— (Cow)
STREAK BLACK OR DARK GRAY— (C 4l )
Color
Name
Hardness
Rcf
Puf/e
Color
Name
Brown
Wad
Brown
Uranmite
Streak Brown
Wad
Wolframite
Dufrenosite
Hornblende1
Hematite
Psilomclane
Tctrahednte
ilmemte
Uranmite
3-5 S
Samarskite
Sidente
Chroniitc
Dark Gray
Sphalerite , Mongamtc Wurtzitc
$ 5-4
Dark Gray
Hrookite Fergusonite
Allaiutc
or Black
Cuprite. Triphte
$ 5-4 4") S
or Black
Frankhnito Homatilo
Thonte
V 5-S S
3 '9
Goethite
4 5-5 S
K)3
Tantahle
Limomtc
t 5"5 5
i3
Rutllo .
Piattnente
5"5 5
Cassiti'nto
Hausmannitc
5"5 5
C'orundunt
Hucbnente
2S
Spinel , ,
Wad
llmcnite
Limonite
i3
Limonite .
Hematite
1*6
BrookiU*
Uranmite
3"5 5
AUanlte
Sidente
J 5-4
Fninkhnhc ,
Sphalente
5-4
Hematite
Brown
Wurtzite
Brown
Columbite. , ,
Thonte ,
Tttiituhtc
Triplite
Braunitc. , , ,
Limonite .
Rutile
Goethite,
4 5-5 5
""W
Cwittirite
Huebnerite . ,
4 5-5 5
Spinel
Wolframite
Limonite
Goethite
Pentlandite
Huebnerite, . . ,
Yellow
Sidente
2Iq
Yellow
Caariterite, .
Sphalerite.
Spinel
Thorite
4 S
f
UxnlnevJ
Ref
jgy
e
2S
ie
38
no
t88
e
20
S
i 6
te
i 6
03
; 6
3?o
e
1 5 M
iw
6 6 s
S5
6 6 s
7
i;r
t
7 5
lt)6
,
4<n
i3
e ,
k
iM
t
7
u;6
4-5 5 S
s 5.5
S, ,
7,S"8
Appendices
A— MINERALS WITH METALLIC LUSTER— (Con)
STREAK BROWN— (Cm)
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Ref Page
Red
Cinnabar Cuprite
Red
Breithauptitc Rutile
Streak Red
Wad
Cuprite
Dark
Hematite
Dark
Wolframite
Gray
Copper
Gray
Samarskite
or
Pyrargynte
or
Frankhnite
5 5-6 5
Black
Tetrahednte
Black
Hematite
Mangamte
Iqi
Columbite
Brown
Wad
Brown
Wolframite
5-5 S
Hematite
Hematite
Copper
Red
Cinnabar Proustite
Red
Gold Hematite
3~6
Pyrargynte
Breithauptitc
Streak Yellow
Sidentc
3 5"4
Dark
Hornblende
Dark
Sphalerite
s?
JL/ili. IS.
firav
Samarskite
Gray
Tnphte
\IJLOljf
or
Brookite
Ss-6
or
Goethite
4 5-5 5
Black
Rutile<
Black
Limonitc
Cassitentc
Hucbncntc
Limomte
Hucbnentc*
4 5-5 5
Sphalerite
s?
Limomte
5-5 S
Brown
Zincite
Brown
Brookite
S 5-6
Tnphte
*73
Rutile
Goethite
4- 5-5 5
Cassitente
Limomte
Goethite,
4 5-5 5
Calavente
"4
Huebnente
4 5-5 S
Yellow
Gold
Yellow
Limomte
5-5 S
Greenockite
Cassitente
Sphalerite
Appendices
A— MINERALS WITH METALLIC LUSTER— (Cow)
STREAK YELLOW — (Cm )
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Ref Page
Sphalerite
Brookite
Red
Zmcite
Iso
Red
Rutile
Goetmte.
4 5-5 5
Streak Green
Urammte
Augite
5~6
Green
Alabandite
Green
Gacloiuute
Hornblende
Spinel
Black, Brown or Red
Alabandite Urammte
Black, Brown or Red
Hucbncntc. Gadohmtc
Streak Cray
Sylvamte
Antimony.
Si
Silver White
Tellurium Bismuth Silver
Silver White
Dyscrasile , Platinum Palladium
Calavente
Indosminc
Molybdenite
Hornblende
Graphite
Augite.
Tetradymite
Hyperbthene
Dark
Silver
Dark
AUanile
S 5 6
Gray or
Biotite Hessite .
Gray or
Anatase . Brookite.
56 S 5W6
Black
Petzite Stromeyente
2 S-3
Black
Perovskite . . Rutile ,
Sphalerite
Gadolinttc
Titamte
5-5 S
Spinel . , .
u;6
Huebnente
Huebnerite ,
Perovskite, ,
46t
Brown
AUamte Anatase
Brown
Rutile Gadolinite, .,
Brookite
Cassilente.. .
Appendices
A— MINERALS WITH METALLIC LUSTER— (Co)
Streak White
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Ref Page
Silver White
Sylvamte Silver Altaite
Silver White
Amalgam Antimony Indium
Biotite
Anatase
Dark
Silver
Dark
Perovskite
Gray
Titanite
Gray
Cassitente
or
Hornblende
or
Garnet
Black
Augite
Black
Tourmaline
Hypersthene
Spinel
Brown
Anatase Perovskite
Brown
Cassitente
B— Minerals With Nonmetallic Luster
Streak Dark Gray Or Black
Color
Name
Hardness
Ref Page
Color
Name
Hardness
gef Page
Dark
Graphite
Dark
Wolframite
Gray or
Melacomte
Gray or
Psilomelane
Black
Wad
Black
Corundum
i "55
Brown
Wad
Streak Brown
Wad
Hornblende
Uranmite
3*5 5
Psilomelane
Dark
Gray f\f
Sidente Sphalerite Cuprite
3 5"4
Dark Gray or
Chromite Uranmite Allamte
Ss-6
2Q7
Black
Thorite Goethite
4 5-5 5
Black
Brookite.
Rutile
S 5-6
I?I
Ferbente
4 5-5 5
Cassitente
Wolframite
5-S 5
Spinel
7 S-8
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Con)
STREAK BROWN — (Coil )
Color
Name
Hardness
Ref Page
Color
Name
Hardnesv
Ref Page
Wad
Sidentc
Hematite
Sphalerite
Limomte
Xenotime
Bauxite
Thorite
Cinnabar
2-2 f
9S
Gocthitc
Pharmaco-
Huebnentc
Brown
sidente
Brown
Wolframite
Chrysocolla
Hornblende
38&
Hematite
Allamte
5-6
Limomte
Brookitc
Bauxite
Rutilc
Olivenite
Cubsiteritc
i6
Uranimte
Spinel
rod
Hematite
153*
HuebntTitc
2S&
Cinnabar
Wolframite
5-5 '
Red
Hematite Cuprite
3-6 "
Reel
Hematite Rutile ,
M3
Sphalerite
Cabbitcnte
Xenotime
Yellow
Bauxite Limomte
Yellow
Goethitc.
">3
Streak Rfd
Dark
Hematite
Dark
Cuprite
*47
Cray or
Gray or
Hematite ,
Black
Black
Brown
Cinnabar
Brown
Hematite
'53
Bauxite
Pyrargyrite
5-3
Hematite
Crocoitc .
Red
Erythnte
Red
Zmcite.
Cinnabar
Xenotime. ,
Proustite
Wolframite
S-S 5
25&
YeUow
Hematite
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Cow)
Streak Yellow
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Ref Page
Dark
Sidente
2Iq
Dark
Brookite
Gray
Huebnente
Gray
Rutile
or
Goethite
4 5-5 5
or
Cassitente
Black
Black
Wad
iSp
Huebnente
4 5-5 5
Limomte
Goethite
4 5-5 5
Brown
Bauxite Sidente
Biown
Brookite Rutile
Sphalerite
8?
Cassitentc
Xenotime
Bauxite
Zmcitc
Red
Wulfemte
Red
Huebnente
4 5-5 5
25*
Vanadmite
Rutile
Sphalerite
Cassitente
Bauxite
Wulfemte
Limonite
Vanadmitc
Orpiment
Greenockite
or
Yellow
Sulphur
Yellow
Pyromorphitc
Autunite
Sphaiente
Carnotite
Zmate
Pharma-
Goethite
ioj
cosidcnte
,,
Crocidolito
W2
Streak Orange
Brown
Thorite
Red
Realgar
Red
Crocoitc
Zincite
Yellow
Greenockite
Yellow
Thorite
ji
Streak Green
Dark
Urammtc
Dark
Augite
Gray
Gray
Spinel
or
or
Black
Black
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Con)
STREAi. GREEN— (COW.)
Color
Name
Hardness
Ref Pago
Color
Name
Hardness
Ref Page
Glaucomte
Brochantite
3~S
Chlorite
Malachite
5-4
Annabergite
1-2 S
Pyromorphite
3 S-4
Torbermte
2-2 S
Dufrenite
Green
Chrysocolla Garmente
Green
Libethemtc Dioptdbe
Pharmaco-
Hornblende
sidente
2 S
2S8
Augite
5*6
Ohvemte
Turquoise
Atacamite
Chlontoid
Streak Blue
Vwamte
Lasunte
Blue
Chrysocolla
Blue
Glau(ophane
Azunte
Dumortientc
33
, Croadohte
Green
Vwanite Crocidohte
Green
Dumorticnte
Streak White
Gypsum
Huebnerite. . ,
4 5 5 5
Halite
Titamte .
Apatite
Glaiuophano
Biotite
Yttrotantahte
S 5-5
Calcite
Hornblende
Dark
Anhydrite
Dark
Augite , .
Gray
Cerussite
Gray
Scheffenle
or
Serpentine
or
Hypersthene ,
Black
WaveUite ,
Black
Wagnerite .
Ankente
AUonite. . ,,
Dolomite
Anatase
S 5 6
Sphalerite
Brookite.
Magnesite .
Perovskite , .
S 5-6
Fluonte
Labradonte ,
6-6 s
*0S
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Con)
STREAK WHITE — (Cm )
Color
Name
Hardnes
Ref Page
Color
Name
Hardness
Ref 1 Page
Epidote
Garnet
3 5-7 5
Dark
Piedmontite.
Dark
Quartz
Gray
Chlontoid
Gray
Tourmaline
or
Gadolmite .
or
Staurohte
Black
Rutile
Black
Spmel
Cassitente
Diamond
Cerargynte
Skorodite
Carnallite .
Strontiamte
Pyrophylhle.
Sidente
Tnpohte .
Pyromorphitc
Kaohnite
Mimetite
Gypsum
Rhodochrosile
Halite
Magnesite
Muscovite
Fluonte
Zinnwalditc
Clmtomte
Phlogopite
Chabazite
Apatite
:66
Harmotomc
Greenockite
Xenotimc
Leadhilhte
Wollastomtc
Biotite
5-3
Apatite
Brown
Chrysotile Stolzite
Brown
Calamine Huebnente
Senarmonlilc
-1 5-3 ,
Lit hiophy lite
Bante
5-3 5
Smithsomte
Vanadimte
Thomsomte
Wulfcmte
Datolite
Calcite
Titanite
Anglesite
Monazite
Serpentine
Yttrotantahtc
S"S 5
Heulandite,
Nephehte
3H
Stilbite
Anthophylhte .
Laumontite
Enstatite ,
Apatite , .
Bronzite.
Dolomite
Hypersthene
Sphalerite ,
Diopside
Wavelhte ,
Hornblende
Aragomte
506 Appendices
B.— MINERALS WITH NONMETALLIC LUSTER— (Con )
STREAK WHITE — (Con)
Color
Name
Hardness
Rof P-ige
Color
Name
Hardness
Ref Page-
Augite
Rutilc
Babmgtonilc
Gddolinitc
Acmite
CaswtcnU'
Fowlente
Andalubitc
Willemite
Vcsuvitimtc
Troostitc
Olivinc
Opal
Garnet
Allanite
Quart K
J59
Anatase
Boraiito .
Brookite
Brown
Danburitc
7 7 S
Perovskite
Tourmaline
Tephroite
Staurohlc
Amblygonitc
Phcnacite
7-H
Chondrodite
Zircon
7
Zoisite
6-6 r
Spinel
7 S
icj6
Sillimanite
ChrysobtT}!
S
Axmite
Corundum
M5
Epidote
Diamond ,
Diasporc
Tqo
Cerargynlc
13
Stol/ilo .
1 &
GlauconJlc
Phlogopitc1
J 5 3
Pyrophylhte
Biotitc . .
S 3
Chrysotilc
Baritc.** ,
a 5 3
239'
Kaohmte
Gibbsitc
3 S 3.S
Vivianite
Wulfcniic, ,
Talc
4Oi
Anhydrite. ,
23
Chlonte
Anglcsite
Green
Annabergite. Orthochlorite
1-2 S
Green
StilWtc Serpentine ,
Melantente
Wavcllilo .,
Halite
Aragomtc . ,
3-S-4
Brucite
Scorodite., .,
3.5"4
*8S
Garmentc ,
Strontianite
Zmnwaldile
Pyromori>hite
3 5"4
Actmolite
Rhodochrobitc
? 5-4 5
Chrysocolla
Fluorite .
W
Leptochlonle
Vanscitc. . .
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Cow)
STREAK WHITE — (Cotl )
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Ref Pago
Scheehte
Amblygomte
Apatite
]r 5-5
Labrador! te
Calamme
t 5-5
Microclme
Triphyhte
Zoisite
Smithsonite
Prehnite
Datohte
Spodumene
Cummmgton-
Forstente
ite
Sillimamte
Grunente
Axinite
Anthophyllitc
Epidote
Gednte
Piedmontite
Thomsonite
Jadeite
Green
Titanite Wagnerite
Green
Diaspore Chlontoid
Hornblende
Gadolmitc
Augite
Andalusite
Acmite
Vesuvianite
Hypersthene
Oh vine
Cancrmite
Fayahte
Nephehtc
3H
Uvarovite
6 5-7 5
33
Scapolite
Quartz
Actmolite
Boraute
Enstatite
Tourmaline
Bronzite
Spinel
Diopside
Beryl
TroostiLe
Topaz
Opal
Chrysoberyl
Turquoise
Corundum
Laumontite
Margante
Gypsum
Dolomite
22Q
Zmnwaldite
'352
Alumte
Lepidohte .
Rhodochrosite
3'5-4 5
Pink
Glauberite
Pink
Fiuonte
tag
Senarmontite
Xenotmie
Kaimte
' 5-3
Apophyllite
Calcite
Lithiophylite
Laumontite
Datohte
508 Appendices
B— Minerals With Nonmetallic Luster—
Streak White— (C(Jw )
Color
Name
Hardness
Rtf Pafje
Color
Name
H irdncss
Ref Page
Wagnente
Zoisile
Sodahte
Epidotc
Cancnmte
Andalusitc
Scapolite
Gurnet
3"
Tremolite
Tourmaline
Pink
Fowlente
S-6
Tmk
Spodumene
Rhodonite
Phcnantc
Bustamite
Topaz
Willemite
Spinel
Tephroite
Corundum
Q
Orthoclase
Carnallile
Ankcrito .
5 4
Kaohnite
Alunite
5 4
Talc
4Oi
Sphalerite
S 4
Laumontitc
Rhotkx hrositc
5 4
Gypsum
Clint onitc, ,
4 S
Thenardite
Chabaite.
4 S
Sylvite
2—2 5
Harmotomo
Halite
PhillipHite.
Glaubente
Xenotime. ,
Phlogopitc
Scheelitc,
*54
StoLnte
Apophyllito, , ,
Red
Gibbsite Kaimte
2 5-3 5 2 5*4
25*
Red
Wollastoniie Apatite , , .
J6
Cryolite
Hubnerite., , ,
4 5 5'3
Calcite
2T4
Analcitc
45
Wulfenite
Natrolhe,
Vanadmite
Thomsonite
Anhydrite
Datohte
Celestite
Titamte... .
Bante*
Monazite
q- e, e
26}
Stilbite ,.
v tf J
Cancrinite, . .
3 £? ' w
*w#
Heulandite
Nephelite, . , ,
Laumontite
3~4
Enstatitc , ,,
Serpentine
Diopside . , ,
37
Dolomite
Rhodonite —
5"6
Aragomte
Willemite
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Can )
STREAK WHITE — (Con )
Color
Name
Hardnes
Ref
Color
Name
Hardnes
Ref
"*
Page
Page
Troostite
Quartz
Opal
Boracite
2Io
Perovskite
Danbunte
Amblygonite
Tourmaline
Orthoclase
Cordientc
Red
Chondrodite
Red
Phenacite
Zoisite
Zircon
Axinite
Beryl
Epidote
Spinel
Iq6
Diaspore
Topaz
S
Vesuviamtc
Chrysoberyl
S 5
Garnet
6 5-7 5
Corundum
Cerargyntc
Vanadmite
Carnalhte
Celestite
Pyrophylhte
Anglesite
Tnpohte
Cerussite
Kaolmite
Heulanditc
3~4
Talc
Stilbite
Chrysotile
Laumontitc
3~4
45*
Orthochlontc
i~3
Serpentine
Gypsum
24?
Margantc
Sulphur
1 5-2 5
Wavelhte
Hanksile
Dolomite
Sylvite
*37
Aragomte
Yellow
Halite
Yellow
Strontiamte
Muscovite
Sphalerite
Phlogopitc
Pyromorphitc
Gaylussitc
Mimetite
Zmnwaldite
Rhodochrosite
3 5-4 5
Glaubente
Magnesite
Leadhilhte
Fluonte
Kamite,
Chabazite
Trona
5-3
Harmotome
Gibbsitc
2 5-3 5
Philhpsite .
Bante
Xenotime
Calcite
Scheelite
KLiesente
Wollastonite
Wulfenne
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Cow)
STREAK WHITE — (Con )
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Kef Page
Apatite
Willemite
Calamme
Opal
Huebnente
Orthoclase
Lithiophylite
Chondrochte
Smithsomte
Epidote
Natrohtc
Rutilc
Thomsomte
Casbitentc
Yellow
Datohte Titamte
Yellow
Andalusite Olivme
S-7
Monazite
Garnet
3*2
Wagnente
Quartz
Sodalite
Tourmaline
Cancnnile
5'6
Zircon
7 S
Nephehte
3H
Top*i8
Scapolite
Spinel
Rhodonite
S-6
Corundum ,
Kaolmite
Smithsomte .
Vivianite
Lasurite .
S S S
Sylvite
La/uhtc
5 S S
Halite
Hciuynite . . .
S-6
Brucite
Sodalite
S-6
Chrysocolia
Cancrimtc.
?6
3*5
Chalcanthite
Nephehte
S-6
3*4
Bante
-' 5-3 5
Scapolile
S-6
Calcite
Willemito . ,
s-fi
Gibbsite
Diopside. ,
S-6
Blue
Anhydnte
Blue
Opal
S S-6
Celestite
Turquoise
Anglesite
Amblygonite.
Aragomte
Glaucophane
6-6 S
Wavelhte
Aximte ,
Skorodite
Diaspore. , ,
Fluorite
Kyanite
Kyamte
45
Vesuvianite, , ,
v /
Apatite
Quartz , ,
*S9
Calamme
Boracite, , . ,
Tnphyhte
Cordiente* . , ,
Appendices
B— MINERALS WITH NONMETALLIC LUSTER— (Con)
STREAK WHITE — (Cofl )
Color
Name
Hardness
Ref Page
Color
Name
Hardness
Ref Page
Tourmaline
Spinel
Blue
Beryl
Blue
Topaz
Corundum
Halite
Quartz
Calcite
Spodumene
Purple
Fluonte Apatite
Purple
Topaz Spinel
Scapolite
Corundum
Tremohte
5~6
Bronze
Phlogopite
Orange
Vanadmite
Orange
Spinel
Streak Colorless Or White
Soda
Halite
£-2 5
Cerargynte
Brucite
Arsenohte
Pharmacohte ,
Carnallite
Senarmontite
Chrysotile
Kauute
Tnpolite
Muscovite
Calcite
Paragomte
Talc
Zmnwaldite
Pyrophyllite
Grunerite .
White
Orthochlorite
White
Gaylussite .
or
Bauxite
*-3
or
Lepidohte
Light
Mirabilite
Light
Apatite
Niter
Gray
Glaubente .
Soda-niter
5"2
Claudetite
Gypsum
Stolzite .
Vivianite
Trona . ,
Melantente
Cryolite
Meerschaum
Gibbsite. ...
Hanksite
Bante . . .
Thenardite
Valentinite
Kaohmte
2-*2 5
Kiesente
Borax
Calcite
Epsomite
Wulfenite
Sylvite
Anhydrite
Appendices
B —MINERALS WITH NONMETALLIC LUSTER— (Con )
Streak Colorless Or Whitf— (C<)U )
Color
Name
Hardness
Ref Page
Color
Name
H irdntus
Ref Page
Celestite
Nephchlc
S-6
Anglesite
Stapohtc
S-6
Cerussite
Trcraohtc
Heulandite
Anlhophyllite
S-6
Stilbite
4$0
EnfeUtite
S-6
Laumontite
Diophiclc.
S-6
Margante
3-4 S
Willcmitc
S-6
Andulusite
S S-6
Alunite
Wayelhtc ,
Lcuntc
S S-6
Dolomite
Beryllomtc.
Aragonite
Amblygonite
Strontianite
Orthoclasc
6-6 s
Sidente
Mknxhne ,
4*3
Ankente
Pluguxlusc. ,
6-6 S
Withente
Prehmtc
Pyromorphite
Spodumenc
Mimetite
Silhm*mitc. ,
White
Rhodochrosite
2 2O
White
Jadcitc .
or
Magnesite
1 5-4 5
or
Axinito ,
Light
Fluonte
Light
Zoisite , ,
Gray
Colemanite
Gray
Diasporo
Chabazite
45
Kyanite ,
Apophylhte
4"5
Andalusite .
6-7-S
Harmotome
4"5
Californite . ,
Philhpsite
Garnet
6-S-7 S
Sia
Pectolite
Quarts . , . ,
Kyamte
4*5
Dumortieritc
Scheelite
4,-Cf
Boracite
2Io
Wollastomte
O
Cordlerite. .,
7-7 S
Apatite
Danburite .
7*7.5
35
Calamuxe
4 5"5
Tourmaline , ,
7"7 5
Smithsorute
Phenacite. , , ,
Analcite
Zircon
3*7
Thomsonite
Beryl .., ,
7 5*8
Natrolite
Topaz . .
Datolite
ChrysoberyL
8,5
Scolecite
Corundum .
I5S
Sodalite
Diamond
Cancnnite
S-6
Appendices
II. LIST OF THE MORE IMPORTANT MINERALS AR- RANGED ACCORDING TO THEIR PRINCIPAL, CONSTITUENTS
Aluminium
Albite
Alum
Alumte
Amblygomte
Analctfe
Andalusite
Anorthite
Augite
Axmite
Bauxite
Beryl
Battle micas
Cancrmite
Celsian
Chabazite
Chrysoberyl
Cordiente
Corundum
Cryolite
Cyanite
Diaspore
Dumortiente
Ar Simony Bournomte Breithauptite Dyscrasite
Arsenates
Arsenic
Arsenolite
Arsenopynte
Chloanthite
Claudetite
Cobaltite
Domeykite '
Epidote
Feldspars
Garnet
Gibbsite
Glaucophane
Harmotome
Heulandite
Hornblende
Jadeite
Kaolin
Kyanite
Laumontite
Lazulite
Lazunte
Lepidolite
Leucite
Margarita
Micas
Microclme
Natrolite
Nephehte
Antimony
Jamesomte Pyrargynte Senarmontite Stephamte
Arsenic
Enargite Erythnte Gersdorffite Lollmgite Munetite "Niccohte Olivemte Orpunent
Orthoclase
Piedmontite
Prehmte
Pyrophyllite
Sillimamte
Sodahte
Spinel
Spodumene
Staurohte
Stilbite
Thomsomte
Topaz
Tourmaline
Turquoise
Uvarovite
Vanscite
Vesuviamte
Wavehte
Zeolite
Zoisite
Many other silicates
Stibmte
Sulphantimorates Tetrahednte Valentimte
Proustite
Realgar
Scorodite
Smaltite
Sperryhte
Sulpharsenites
Tennantite
Appendices
Barite
Celsian
Bertrandite
Beryl
Beryllomte
Bismite Bismuth
Axinite Boracite Borax Colemanite
Bromyrite
Greenockite Pollucite
Actinohte
Andradite
Anhydrite
Ankente
Anorthite
Apatite
Apophyllite
Aragonite
Asbestus
Augite
Autunite
Babingtonite
Bustamite
Calcite
Cancnnite
Carnotite
Barium
Harmotome Hyalophane
Beryllium
Chrysoberyl Gadoliriite
Bismuth
Bismuthmite Bismutite
Boron
Danbunte
Datohte
Dumortiente
Bromine
Embohte
Cadmium
Caesium
Calcium
Chabazite
Colemanite
Danbunte
Datohte
Diopside
Dolomite
Epidote
Fluonte
Gaylussite
Glaubente
Grossulante
Gypsum
Harmotome
Heulandite
Hornblende
Laumontite
Psilomelane Withente
Herdente Phenacite
Sulpho-bismuthimtes Tetradymite
Sassolite
Tourmaline
Ulexite
lodobromite
Margarita
Perovskite
Phillipsite
Picdmontite
Prchnitc
Scheehte
Sooledte
Stilbitc
Thomsonite
Tftanite
Tremolite
Uvarovite
Vesuvianite
Wollastonite
Zoisite
Many other silicates
Appendices
Carbon
Cancrmite Carbonates
Allamte
Fergusomte
Gadolimte
Apatite
Atacamite
Boracite
Carnalhte
Cerargynte
Diamond Graphite
Cerium
Monazite Samarskite
Chlorine
Cryolite
Halite
Hanksite
Kamite
Mimetite
Hanksite
Thorite Xenotime
Pyromorphite
Scapohte
Sodahte
Sylvite
Vanadmite
Chromite
Chromium
Crocoite
Uvarovite
Cobaltite Erythnte
Columbite
Columbates
Fergusomte
Atacamite
Azunte
Berzelianite
Bornite
Bournonite
Brochantite
Chalcanthite
Chalcocite
Chalcopyrite
Allamte Cerite
Cobalt
Glaucodite Linnaeite
Columbium
Samarskite Polycrase
Copper
Chrysocolla
Copper
Covelhte
Cuprite
Cypnne
Dioptase
Domeykite
Enargite
Libethenite
DIDYMIUM Gadolinite
Smaltite
Tantalite YtrrotantaJite
Malachite
Melacomte
Ohvenite
Stromeyente
Tennantite
Tetrahednte
Tenorite
Torbermte
Turquoise
Monazite
Appendices
Allanite Fergusonite
Amblygomte
Apatite
Chondrodite
Cryolite
Durangite
Argyrodite
Calaverite Gold
lodyrite
Iridosmine
Erbium
Gadolmite Xenotime
Fluorine
Fluonte
Herdente
Lepidolite
Phlogopitc
Tourmaline
Germanium
Gold
Petzite
Sylvamte
Iodine
Marshite
Irtdium
Yttrotantahte
Topais Tnplitc Vesuvianite Waguentc
Conficldite
Krenncrite
Mteraitc
Platfniridium
Actmolite
Almandite
Andradite
Ankerite
Anthophyllite
Arsenopynte '
Augite
Biotite
Babmgtonite
Bormte
Bronzite
Chalcopyrite
Chromite
Columbite
Cordierite
Crocidohte
Cummingtonite
Dufremte
Iron
Fayahte
Ferberite
Franklinite
Gadolinite
Gedrite
Glauconite
Goethite
Greenaljte
Gruenerite
Hematite
Hornblende
Hypersthene
Ilmenite
Iron
Lepidomelaae
Limomte
LoJlingite
Magnetite
Marcasite
Melontcrite
OKvine
Pen tlaiK lite
Pharnmconiderite
Pyrite
Pyrope
Pyrrhotite
Scorodite
Sidertte
Staurolite
Tantalite
Triphylite
Triplite
Turgite
Vivianite
Wolframite
Many other silicates
Appendices
sir
Altaite
Anglesite
Bournonite
Cerussite
Clausthahte
Crocoite
Descloizite
Dufrenosite
Amblygonite
Lepidolite
Lithiophihte
Actmolite
Ankente
Anthophylhte
Asbestus
Augitc
Biotite
Boracite
Brittle micas
Bronzite
Brucite
Carnalhte
Chlontes
Chondrodite
Chtysotile
Alabandite
Babmgtonite
Bra unite
Bustamite
Columbite
Fowlente
Frankhnite
Hauerite
Hausmanmte
Lanthanum
Monazite
Lead
Galena
Phosgenite
Jamesomte
Plattnente
Lead
Pyromorphite
Leadhilhte
Stolzite
Massicot
Uramnite
Mimetite
Vanadimte
Minium
Wulfenite
Lithium
Spodumene
Petalite
Tnphyhte
Zinnwaldite
Magnesium
Cordiente
Kieserite
Cummmgtonite
Leptochlontes
Diopside
Magnesite
Dolomite
Meerschaum
Enstatite
Ohvine
Epsomite
Phlogopite
Forstente
Pyrope
Garmente
Serpentine
Gedrite
Spinel
Glaucophane
Steatite
Hornblende
Struvite
Hydromagnesite
Tremolite
Hypersthene
Wagnente
Kamite
.Many other silicates
Manganese
Huebente
Rhodonite
Lithiophihte
Scheffente
Manganite
Spessartite
Manganotantalite '
Tantalite
Piedmontite
Tephroite
Polianite
Triplite
Psilomelane
Troostite
Pyrolusite
,Wad
Rhodochrosite
Wolframite
Appendices
Amalgam
Calomel
Cinnabar
Molybdenite Molybdite
Annabergite
Breithauptite
Chloanthite
Garniente
Genthite
Niter
Mercury
Coloradoite Metacmnabarite
Molybdenum
Powellite
Nickel
Gersdorffitc
Linnaote
Melonitc
Mjllente
NITKOCt N
Onofnte
Tiemannite
Wulfcnitc
Niccolite
Pentlandite
Ullnwnite
Zaratite
Soda-niter
Indosmine Palladium
Osmium
Palladium
Phosphates PI atinir idium
Alunite
Apophyihte
Biotite
Carnallite
Carnotitc
Glauconite
Hanksite
Harmotome
Aguilante
Berzelianite
ClausthaHte
Phosphorus Platinum
Platinum
Potassium
Jarosite
Kainite
Kahnltc
Lepidolite
JLeucitc
MJcrocline
Muscovite
Nephelme
Selenium
Naumannite 'Oxxofrite
Sperrylite
Niter Orthodasc
Phlogopite
Psilomelanc
Sylvitc
Many other silicates
Selen-tellurium Tiemannite
Appendices
Opal
Silicon
Quartz
All silicates
Silver
Amalgam
Argentite
Bromynte
Calavente
Cerargynte
Dyscrasite
Embolite
Hessite
lodynte
Petzite
Miargynte
Pearceite
Polybasite
Proustite
Pyrargynte
Silver
Stephanite
Stromeyente
Sylvamte
Tetrahedrite
Acmite
Albrte
Analcite
Beryllonite
Borax
Cancnnite
Chabazite
Crocidohte
Cryolite
Durangite
Gaylussite
CcIestJte
Arsenopynte
Brochantite
Cobaltite
Hanksite
Hauymte
Kaimte
Columbite Fergusonite
Altaitc Calaverfte ColoradoHe Hessite
Sodium
Glaubente
Glaucophane
Halite
Hanksite
Jadeite
Lasunte
Mirabilite
Natrolite
Natron
Nephehte
Strontium Sulphur
Lazunte
Leadhilhte
Marcasite
Noselite
Pyrite
Tantalum
Samarskite TantaLte
Tellurium
Krennente Melonite Nagyagite Petzite
Paragonite
Soda
Sodalite
Soda-niter
Stilbite
Thenardite
"Thomsomte
Trona
Ulexite
Many other silicates
Strontiarute
Pyrrhotite
Sulphates
Sulphides
Sulpho-salts
Sulphur
Yttrotantahte
Selen-tellurium Sylvawte Tellunte Tetradymite
Appendices
Crookesite
Thallium
Loranditc
Aeschynite Monazite
Thorium
Pyrochlore Thorite
Uraninitc Yttnalitc
Canfieldite
Anatase
Astrophylhte
Brookite
Tin
Cassiterite
Titanium
Ilmenite
Perovskite
Pseudobrookite
Stannitc
Rut ilc
Schorlomfle
Titanite
Ferberite Huebnerite
Tungsten
Polycrase Scheehte
Stohsile Wolframite
Autunite Carnotite
Uranium
Gummite Torbernite
Uranimte Uranophanc
Carnotite DescJoizite
Vanadium
Patronite Roscoelite
Vanadinite
Allanite
Fergusonite
GadoJinite
Yttrium
Samarskite Xenotime
Yttrialite Yttrotantalite
Calamine Fowlerite Franklinite Gahnite
Zinc
Goslarite Hydrozincite Smithsonite Sphalerite
Troostite Willemite Wurtzite Zincite
Baddeleyite
Zirconium
Zircon
Appendices
Yielding Water In Closed Tube
Allanite
Alunite
Analcite
Annabergite
Apophyllite
Atacamite
Autunite
Axuute
Azunte
Bauxite
Biotite
Borax
Brochantite
Brittle micas
Brucite
Calamme
Cancrmite
Carnalbte
Chlontes
Chondrodite
Chrysocolla
Chrysotile
Colemamte
Cordiente
Datoiite
Diaspore
Dioptase
Dufremte
Dumortiente
Epidote
Epsomite
Garni en te
Gaylussite
Gibbsite
Glauconite
Goethite
Gypsum
Kainite
Kaohnite
Kiesente
Lazuhte
LeadhiUite
Lepidohte
Libethenite
Limonite
Malachite
Mangamte
Margante
Meerschaum
Micas
Mirabihte
Muscovite
Olivemte
Opal
Piedmontite
Phaimacohte
Pharmacosiderite
Phlogopite
Prehnite
Psilomelane
Pyrophylhte
Skorodite
Serpentine
Staurolite
Steatite
Struvite
Torbernite
Tourmaline
Topaz
Trona
Turquoise
Vanscite
Vesuvianite
Viviamte
Wad
Wavelhte
Zeolites
Zmnwaldite
Zoisite
Iil List Of Minerals Arranged According To Their Crystallization
Bauxite Chrysocolla Garmente Glauconite
AMORPHOUS (probably colloidal)
Limonite Opal
Psilomelane Pyrolusite (?)
Skorodite Turquoise Wad
Arsenolite (?) Boraate above 265° a-Cristobaiite
Isometric
Lasurite
Leucite above 500°
Senarmontite (?) Uraninite
522 Appendices
Hexoctaiiedral Class (Holohedrai)
Altaite
Frankbmtc
Magnetite
Amalgam
Gahmte
Mercury
Argentite
Galena
Palladium
Bormte
Garnet
Petzite
Cerargynte
Gold
PlCOtltC
Chromite
Halite
Platinum
Clausthalite
Hessite
Srhorlormte
Copper
Iron
Silver
Fluorite
Lead
DYAKISDODECAHEDRAL CLASS (HfcMJUJJLDRAL)
Alum
Cobaltite
Smalt it c
Chloanthite
Pynte
Spcrryhle
Hextetrahedral Class
(HfcUHIEDRAL)
Alabandite
Nosehte
Sphalerite
Boracite
Pentlandite
Tetrahodnlc
Diamond
Perovskite (?)
Tcnnantitc
Hauymte
Pharmacobiderite
Tiemannite
Metacinnabante Sodalite
PENTAGONAL ICOSITKTK ATI K ORAL CLASS Cuprite Rylvite
PSEUDO-ISOM KTRTC Analcite Leucite Perovskite
Hexagonal
Breithauptitc Hanksite Pyrrhotite (?)
Carnotite (?) Molybdenite 0 Tridymite
Covellite Niccolite
DIHEXAGONAL BIPYRAMIDAL CLASS Beryl Cancrinite
DIHEXAGONAL PYRAMIDAL CLASS (HOLCMIEMIMOKPHIC) Greenockite Wurtzile Zincitc
HEXAGONAL BIPYRAMIDAL CLASS (HEMIHEDSAL) Apatite Mimetite Pyromorphite Vanadinite
Appendices 523
HEXAGONAL PYRAMIDAL CLASS Nephelite
HEXAGONAL TRAPEZOHEDRAL CLASS jS Quartz
Ditrigonal- Scalenohedral Class (Hemihedral)
Alumte Corundum Selenium
Antimony Graphite Sidente
Arsenic Hematite Smithsomte
Bismuth Indosmme (?) Soda-niter
Brucite Magnesite Tellunum
Calcite Millente Tetradymite
Chabazite Rhodochrositc
DITR1GONAL PYRAMIDAL CLASS (HEMIHEDRAL-HEMIMOBPHIC) Ice Tourmaline Proustite Pyrargynte
TRIGONAL TRAPEZOHEDRAL CLASS (TETARTOHEDRAL) Quartz Cinnabar
Trigonal Rhombohedral Class (Tetartohedral)
Ankente Phenacite Willemite
Dioptase Troostite Dolomite
Ilmemte
TETRAGONAL a Cnstobakte (?)
Ditetragonal Bipyramidal Class (Holohedral)
Anatase Phosgenite Rutile
Apophyllite Plattnente Vesuvianite
Braunite Pohanite Xenotime
Cassitente Thorite Zircon
Hausmanmte Torbernite
TETRAGONAL SCALENOHEDRAL CLASS (HEMIHEDRAL) Chalcopyrite
524 Appendices
TETRAGONAL BIPYRAM1DAL CLASS (Hi MIIII OKAI)
ManaJite Scapolitc Wcrnonte
Meiomte Scheelitc Wulfemlc Mizzonite
Orthorhombic
Acanthite Dumorticnlo Samnrhkile
Anthophylhle (?) Enslatitc (?) Serpentine
Boracite below 263° (?) St rat it c (i)
Bronzite (?) Hypcrsthcne (?) Tantalite
Brookite Jamcsomtc Trulyniitc
Chrysotile (?) Kaohnite (?) Thomsorute
Columbitc Meerschaum (?) Vans<itt*
Domeykite Porovskite (?) Vilrotantahie
Dufrenite PyrophylHlc (?)
ORTHORHOMBTC B1PYKAM1OA1- CM-ASS (ric.nnn IIRAI)
Andalusite Cordiente Sillirnnnit e
Anhydnle Danbuntc Skoroclitc*
Anglesitc Diaspora Slituroht e
Aragonile Dyskrasite SU'phnnile
Arsenopyri 1 e Kn argi to S 1 1 bn i t e
Atacamite Kiyahte Htromcy<Ttte
Autumte Forsterile Ht ront iunit c
Bante Glducodot Sulphur
BeryUonite Gocthitc Tcphroit e
Bismuthmite Libethenite Thcnardil c
Bournonitc IJthiophilite Topu
Brochantite Lollingfte a Truly mite
Brookite Manganite Triphylite
Carnallite Marcasile Valcntint'te
Celestite Natrohte Wavellilc*
Cenassite , Niter Withcrilc
Chalcocite Olivcnlte Zoisitc
Chrysoberyl Olivine
ORTHORHOMBIC B1SPHENOIDAL CLASS Epsomite
Orthorhombic Pyramidal Class
Bertrandite Prehnite Struvlte
Caiamme Stephanite
Appendices
Monoclinic
Anthophylhte (?)
Durangite
Meerschaum (?)
Antigonte
Enstatite (?)
Natron
Bronzite (?)
Gednte (?)
Pennmite
Chlontes
Gibbsite
Prochlonte
Chlontoid
Herdente
Pyrophylhte (?)
Clmochlore
Hypersthene (?)
Serpentine (?)
Clintomte
Kaolmite (?)
Steatite (?)
Monoclinic Prismatic Class
(Holohedral)
Acmite
Dufrenoysite
Mirabihte
Actmolite
Epidotc
Monazite
Adulana
Erythnte
Muscovite
Algirme
Fassaite
Orpiment
Allanite
Ferbente
Orthoclase (?)
Annabergite
Gadolmite
Paragonitc
Anomite
Gaylussite
Pearceilc
Amphibole
Glaubentc
Pectohte
Arfvedsomte
Glaucophane
Pharmacolite
Augite
Grunente
Philhpsjte
Azunte
Gypsum
Phlogopite
Barbiente (?)
Harmotome
Picdmontite
Barytocalcite
Hedenbergite
Polybasite
Biotite
Heulandite
Realgar
Borax
Hornblende
Riebcckite
Brushite
Huebnerite
SahLte
Calavente
Hyalophane (?)
SchefFerite
Celsian (?)
Jadeite
Spodumene
Chondrodite
Kainite
Stilbite
Claudetite
Kiesente
Titamte
Clmochlore
Laumontite
Tremolite
Clinohumite
Lazulite
Colemanite
Leadhillite
Trona
Crocidolite
Lepidolite
Vivianite
Crocoite
Lepidomelane
Wagnente
Cryolite
Malachite
Wolframite
Cummmgomte
Margante
Wollastonite
Datohte
Melantente
Zmnwaldite
Diopside
Meroxene
Scolecite
MflNOCLINIC DOMATIC CLASS (HEMIHEDRAL)
Appendices
Trjclinic
Aenigmatite Fremontite Montchrasite
Amblygomte Melacon 1 1 e 1 'u rq u
Triclinic Pinacotdal Class
Aenigmatite Babingtonite Labradorit e
Albite Bustarnite MicrorJinc
Andesine Bytownite Oligcx hisc
Anemousite Celsian (?) Orthotlase (?)
Anorthite Chalcanthite Rhodonite Anorthociase Fowlente Aximt e Kya.ni t e
Iv. Reference Books
GENERAL TEVTS Handbuch der Mmeralogie, by Dr Carl Hintze Veit & Comp , Leipzig, 1897 —
(2 volumes) System ot Mineralogy (6th edition), by E S Dana John Wiley & Sons, New York,
1892 ist Appendix, 1899 2d Appendix, 1909 3d Appendix, 1916 Useful Minerals of the United States, by S Sanford and R W Stone U S
Geological Survey Bulletin No 624 Washington, D C , 1917
DETERMINATIVE TABLES Determinative Mineralogy with Tables, for the Determination of Minerals by
Means of Their Chemical and Physical Characters, by J. V Lewis John Wiley
& Sons, New York, 1913 Manual of Determinative Mineralogy (i6th edition), by Geo J Brush and S L
Penfield John Wiley & Sons, New York, 1906 Tables for the Determination of Minerals, by E H Kraus and W F Hunt.
McGraw-Hill Book Co , New York, 1911
Crystallography
Crystallography, by T L Walker McGraw-Hill Book Co , New York, 1913* Elementary Crystallography, by W S Bayley McGraw-Hill Book Co, New
York, 1910 Essentials of Crystallography, by E H Kraus, George Wahr, Ann Harbor, Mith ,
Grundnss der Knstallographie, by Dr G Verlag von Gustav Fischer,
Jena, 1913
Physical Properties
Optical Properties of Crystals, by P Groth Translated by B H Jackson John Wiley & Sons, New York, 1910
Physikabsche Krystallographie (4th edition), by P Groth Wilhelm Engelmann, Leipng, 1905
Rock Minerals (2d edition), by Jos P Iddmgs. John Wiley & Sons, New York,
Petrographic Methods, by E Wemschenk. Translated by R W Clark. McGraw- Hill Book Co , New York, 1912
CHEMICAL PROPERTIES Handbuch der Mmeralchemie, 4 volumes, edited by C Doelter Theodor Stein-
kopff, Dresden and Leipzig, 1912 Chemische Krystallographie, by P. Groth Wilhelm Engelmann, Leipzig, 1906,
1908, 1910
The Data of Geochemistry, by F W Clarke Bulletin No 616 U. S Geological Survey, Washington, 1916.
528 References
Origin And Associations
Economic Geology (4th edition), by Hcmru h Ries New York, The Examination of Prospects, by C G (iunihcr MUJraw-Hill Book Co , New
York, 1912
Gems and Minerals, by 0 C Farnngton. A W Mum ford, Chicago, 1903 The Nature of Ore Deposits (ad edition), by Or R, Beik TrunbUted by W. H.
Weed McGraw-Hill Book Co , New York, 191 1
The Non-Metallic Minerals, by G P Merrill, John Wiley & Sons New York, 1910. Mineral Deposits, by W McGraw-Hill Book Co , New York, 1913.
Alterations
A treatise on Metamorphism, by C. R Van Hibe. U. 8. Geological Survey, Mono- graph, Vol 47, 1904, Washington, I), C.
A Treatise on Rocks, Rock-weathering, and Soils, by Merrill The MacmiUan Co , New York, 1906
General Index
Acid arsenates, 292 Acid phosphates, 279, 292 Acid silicates, metasihcates, 397
orthosihcates, 343 Acids, silicic, 300 Albite twinning, 419 Alkali amphiboles, 390 Alkali feldspars, 413 Alkali micas, 353 Alkali pyroxenes, 375 Alteration of minerals, 30 Alteration pseudomorphs, 31 Alum group, 246, 251 Alummates, 195 Aluminium, tests for, 483 Alummosilicic acids, 301 Analyses, calculation of, 4
records, of, 6
Analysis, blowpipe, 12, 467 microchemical, 13 wet, 4
Andalusite group, 319 Anhydrous arsenates, 261
basic, 274 Anhydrous carbonates, 212
basic, 231
Anhydrous metasihcates, 359 orthosihcates, 302 polysihcates, 426 tnmetasihcates, 408 Anhydrous phosphates, 261
basic, 274
Anhydrous sulphates, 236 Antimomdes, 68, 77
metallic, 77, zoo Antimony, tests for, 483 Apatite group, 266 Aragomte group, 223 Arrow-head twin, 248 Arsenates, 261 anhydrous, 261
Arsenates, anhydrous, basic, 274
normal, 261 hydrated, 281
basic, 274, 286
normal, 281 Arsenic group, 49 Arsenic, tests for, 483 Arsenides, 68, 77
metallic, 77, 100 Arsenohte-claudetite group, 151 Atmospheric water, deposits from, 20 Atomic weights, 6
Bante group, 238
Barium, tests for, 483
Basic arsenates, 274
Basic anhydrous arsenates, 274
Basic anhydrous carbonates, 231
Basic anhydrous phosphates, 274
Basic carbonates, 231
Basic hydrated arsenates, 286
Basic hydrated phosphates, 286
Basic metasihcates, 393
Basic orthosihcates, 319
Basic phosphates, 274
Basic silicates, metasihcates, 393
orthosihcates, 319 Basic sulphates, 243 Basic sulpho-salts, 124 Basic vanadates, 288 Baveno twinning, 411 Beads, 476
borax, 476
microcosmic salt, 477 Bellows, 468 Bismuth, tests for, 484 Blende group, 87 Blowpipe tests for aluminium, 483
antimony, 483
arsenic, 483
banum, 483
General Indbx
Blowpipe tests for bismuth, 484
boron, 484
bromine, 484
cadmium, 484
calcium, 485
carbonates, 485
chlorine, 485
chromium, 485
cobalt, 483
columbium, 485
copper, 486
fluorine, 486
gold, 486
iodine, 487
iron, 487
lead, 488
lithium, 488
magnesium, 488
manganese, 488
mercury, 489
molybdenum, 489
nickel, 489
nitric acid, 489
oxygen, 490
phosphoric acid, 490
potassium, 490
selenium, 490
silicon, 490
silver, 491
sodium, 491
strontium, 491
sulphur, 491
tantalum, 491
tellurium, 491
thallium, 492
tin, 492
titanium, 499
tungsten, 492
uranium, 493
vanadium, 493
zmc, 494
zirconium, 494 Blowpipes, 468 Blowpipe analysis* 467 Blowpipe apparatus, 469 Blowpipe flame, 470
oxidizing, 470
reducing, 470 Blowpipe reagents, 469
Bondn/a, 21 Routes, 20<?, tod Borax beads, 47<) Boron, tests for, 4S; Brittle micas, 40 Bromides, r $4 Bromine, tests for, 48 1
Cadmium, tests for, 484 Calute group* 2 1 Cak ite-aragonite group, Jta Calcium nut us, ,152 Calcium, tests for, 48 Calculation of analysts, 4 Calculation of formulas, to Carbonates, 212
anhydrous, 21 Jt normal, at a btwit, ai
hydrous, 234 Carbonates, tests for, 485 Carbon group, ,47 Carlsbad twinning, 410, 4*0 (Yrargyrite group, i tf ChaUotite group, 84 Charcoal, use of, 47,$
Chemical Hubatatuvs an mi
Chlorine, tt?st for, 485 Chlorite group,
Chromatea, 253
Chromitcs, IQS
Chromium, for, 485
Cinnabar group, t)7
Claasification of minerals, 15
Clay ironstone, 154
Closed tube, ue of, 471
Cobalt, tents for, 48$
Cockscomb twin, MO
Colored beads, 476, 477
Colored flames, 477
Columbates, 293
Columbium, test for, 485
Combined water, n
Composition of minerals, 4
Composttlonof waterof Atlantic Ocean, 4
General Index
Composition of water of Borax Like,
Dead Sea, 23
Great Sail Lake, 21
Goodenough Lake, 23
Uike tteisk, Contact minerals, 2? Copper test, 480 Copper, tests for, 480 Corundum group, 152
Datolite group, 4*4 Decomposition, of rocks, 20
of minerals, 30 Deposits from atmospheric water, 20
hot springs, 22
lakes, 22
magmatie water, 23
springs, Ji
Dctet tion of nlkahes, 470 Detection of alkaline cart 1m, 470 Detection of elements by flame colors,
Determinative1 mineralogy* 467
Diantimonicles, 100
Diareenides, too
Dia[K)re group, i8g '
Differentiates, 25
Dike, 28
Dioxides, 158
Diselenideft, 100
Disulp>hidea, 68, 100
Ditcllurides, 100
Dolomitic limestone, 220
Double carbonates with sulphates, 252
Double chlorides, 142
Double chlorides with sulphates, 351
Double sulphates, 251
with carbonates, 251
with chlorides, 351 Double fluorides, 149 Druse, 21, 38 Dyskrasite group, 77
Kclogite, 3QX
Klbow twin, 172, 173, 3x7
Elements, 36
Epidote group, 326
Epsonite group, 246, 249
Feldspar group, 408 1'erntcs, ig$ lames
blowpipe, 470
candle, 470
colored, 477
oudumg, 470
reducing, 470 Kluoncles, 14, 130, 142 Muorme, tests for, 486 formation of minerals, 17 Formulas, cak ulation of, 6, ID
Galena group, 78
Garnet group, 308
Ge-nthite, 400
(Jeotles, 29
Glan/, group, roo
(Sold, tests for, 486
Gossan, 104, 185
Guide to descriptions of minerals, 495
Honestonc, 16$
Hot springs, dqwsits from, 22
Hydrutcd arsenates, 281
ACi<i, 2Q2
Imau, 286
normal, i8 1
Hydratod carbonates, 234 Hytlnited phosphates, 281
acid, 292
basic, 286
normal, 281 Hydrated silicates, 441 Hydratcd sulphates, 246 Hydroxides, tjg
Impregnations, 20 Iodides, 134 Iodine, tests for, 487 Iron, tests for, 487
Key to mineral descriptions, 407 with metallic luster, 407 with nonmetallic luster, 501
Lake George diamonds, 164 Lakes, composition of water of, 95 deposits from, 20
General Indkx
Lead, tests for, 488 Limestone, 216
dolomitic, 229
Lists of minerals according to compo- sition, 513
according to crystallisation, "jar List of reference books, 527 Lithium, tests for, 488 Lithium-iron micas, 352 Lithographic stone, 216
Magmatic water, 23
Magnesium - calcium - iron amphiboles,
Magnesium-calciunviron pyroxenes, 370 Magnesium-iron micas, 349 Magnesium tests for, 488 Manebach twinning, 411 Manganese, tests for, 488 Manganites, 195 Marble, 216 Marcasite group, xoq Mechanical pseudomorphs, 32 Melantente group, 246, 249 Mercury, tests for, 489 Metallic antimomdes, 77, too Metallic arsenides, 77, 100 Metalloids, 37 Metals, 52 Metaxnorphism, 24
contact, 2$
dynamic, 26 Metasihcates, 359
anhydrous, 359 normal, 359 basic, 393 acid, 397
Metasomatism, 24, a$ Mica group, 348 Mica twinning, 344, 427, 430 Microchemic&l analysis, 13 Microcosmic salt beads, 477 Millente group, 94 Mineral names, 36 Molybdates, 253, 254 Molybdenum, tests for, 489 Monoantimomdes, 77 Monoarsenides, 77 Monoclinic anpkiboles, 382, 384
Monotlinii pyrmenes, Monoselemdes, 77 Monosulphides, (H, (Q, 77 Monotellu rules, ;; Monoxides, 140
Nelsomte, jog Ncphelm? group, Nickel, tests for, Nitrates, 20 Nitric utul, tests for, 480 Non-me tills, 37
Ocrurromc, of minerals, Ocean, umiposition til water of,
deposits from, ut Ohvenite , 77 Olivine group, oa Oolitic* ore, 154 Open tube, use of, 47* Orgarm secretittns, .*o Origin of minerals, 1 7 Orthorhombit amphiboles, Orthorhomlie pyroxenes, Orthomlirates, viOk
anhytirourt, ,*oj 30 a
acid, J
Oxides, 146 Oxychloruies, 144 Oxidising flame, 470 Oxygen, testa for, 4jo
Paramorpha, ,v Partial pseudomorphft, 31 Pennine twinning, 4*g, 430 Pencline twinning, 430 Phosphates, a6i anhydrous, 361
acid 279
basic, 274 hydrated, 281
acid, 292
bask, 286
General Index
Phosphoric acid, tests for, 490 Placer, 20
Platinum-iron group, 63 Pneumatolysis, 17, 25 Pncumatolytic products, 25 Polysihcates, anh>drous, 426 Potash-barium feldspars, 416 PoUssium, tests for, 490 Precipitation, 18, 20
irorn atmospheric water, 20
from magmas, 25
from ocean, 22
from solutions, 18
from springs, Jt Primary minerals, 17 Pseudomorphs, 30
alteration, 31
chemical, 32
mechanical, 32
partial, 41
Pseudowollastomt e, 369 Pyrargyrite group, xi; Pyritc group, 101
Quartette, 165
Record of analyses, 6 Reducing ilame, 470 Reduction tests, 482 Rhombic section, 420 Rutile group, i6S
Sandstone, 165 Scapolite group, 423 Scheehte group, 254 Screens, 477, 47 Secondary enrichment, 33, 34 Selemdes, 68, 6(> of the metalloids, 6t> of the metak, 77, too Serpentine group, 397 Sesquioxides, 151 Silica, 158 Silicates, 300 anhydrous, metasthcates, 350 orthosilicates, 302 trimctasilicates, 408 polysihcates, 426
Silicates, hydrated, 441 Silica group, 158 Silicates, hydrated, 441 Silicic acids, 300 Silicon, tests for, 490 Silver, test for, 491 Soapbtonc, 401 boda-hmc feldspars, 417 Socialite group, 330 Sodium, tebtb for, 491 Solidification of magmas, 25 Solubility of minerals,
in water, 18, 19
in carbonated water, 20 Spearhead twin, no Sphalerite group, 87 Spinel group, 195 Spinel twinning, 196 Springs, deposits from, 21 Stalactite, 21, 216 Stalagmite, 216 Stibnitc group, 72 Strontium, tests for, 401 Sulphantimonates, 116, 122 Sulphantimonites, no, 117 Sulpharsenates, no, 2*2.2 Sulpharsenites, 116, 117 Sulphates, 236
anhydrous, 236 basic, 243 normal, 236
hydrated, 240 Sulphdiantimomtes, m Sulphdiarsenitcs, 122 Sulphides, 68
of metalloids, 6g
of metals, 77, 100 Sulpho-ferrites, n, 129 Sulpho-aalts, 116
basic, 124
ortho, 117 Sulphur group, 47 Sulphur, tests for, 49X Swallow-tail twin, 247 Sylvamte group, 113 Synthesis, 15
Tantalates, 293 Tantalum, tests for, 491
General Indhx
Table of atomic weights, 7 Tellurides, 68, 69
of metalloids, 69
of metals, 77, 100 Tellurium, tests for, 491 Tests with cobalt solution, 480
with HC1, 482
with HKSO<, 481
with magnesium nbbon, 482
with metallic zinc, 482
with Na8CO , 480 Tetradymite group, 75 Tetrahednte group, 126 Thallium, tests for, 492 Tin, tests for, 492 Titanatcs, 461 Titanium, tests for, 492 Titano-silicates, 461 Triclmic amphiboles, 383, 393 Tnclimc pyroxenes, 365, 380 Tnmetasihcates, 408 Tungstates, 253, 254 Tungsten, tests for, 492
Ultramarine, 343 Uranates, 203 Uramte group, 288 Uranium, tests for, 493
Vanadates, 261 normal, 261
Vanadates, V.in.idium, tests for, 493 Vadose water, Jt Veins, 21, 24, 2 7, 28 Verd-tintique, 99 Vitriol group, .'49 Vi\ unite group, &i
e gnnip, 273 \V,iter, atmosphcru , ticposits from, 20 \VattT, (drlxmatmi, stiluhilit} tif .iK
in, 20
Water, lomhint'tl, n
Water, lakes ami win, cumptit ion of, j Water, magmatu, Water tf t rystalli/ution, 1 1 Water, solubility of minerals in, 18, i<), jo Water, vati*se, ;i Weathering, ,jj Whetstone, 105 Willcfflite group, ,406 Wolframite group, 358 Wollastonite subgroup, 368 WurUite group, 90
Zeolite group, 445
Xinc, tets for, 404
Xirionium, tent 8 for, 494
Zone of secondary enrichment, 33
Index Of Minerals
Tht italicized figures are tho numbers of the page* on which the principal descrip- tions appear*
Athroite, 436
At mite, 305, ???, 506, 507
Ac tinohU , 382, jA'rt, 500, 507
Adulana, 414
Acginne, 36$,
Atginnc-augitc, l?j
Acmgmatitc, 38$, 393
Agdlmatolitu, 406
Agate, 164
Agmluntc, 78
Alabandihs 87, yot 500
Alabaster, 248
AlgodomU', 78
Allanite, 326, 730, 498, 500, 501, 502,
504, 506
Allopalladjum, rf<5 Ailophams 404 Almunditc, 30 ?/2 Afatomte, 331 Alum, 246) 351
Alunite, 243* 344, W, 50 Amalgam, 53, tf?, 50* Amazomte, 41 Amber mica, 350 Amblygonite, 274, 503, 506, 507, 5oo>
Amethyst, 164 Oriental, 156 Amphiboloids, 363 Amphiboles, 363 Anakite, 446, 4$ Anataae, 167, 176, 500, 501, 504, 506 Andalusite, 310, 390, 506, 507, 508, 512 Andesme, 4i74/<? Andradite, 309, 312 Anemousite, 408, 418 Angleeite, 238, 140, 505, 508, 509, 5*o, 5"
Ankente, 20, 504 ,508, 512
Annabcrgitc, 281, sti 5,04, ?o6
Anoxmtc, w
Anorthitc, 301, 408, 40, 417, 418
Anorthtu lasc, 413, 418
Anthracite, 4$
Anthophylhtc, 382, o?, 507
AntiKontc, 308, 428
Antimony, 49,51, 500,501
Apatite, 26 1, 266, 504, w, 507, ipA,
Apophylhte, i<?, ,/./?, 07, 508, 512 Aquamarine, 361 Aragomtc, 21, 26, p, 212, 333, 505, 506,
508,500. 510,512 Arfvedsonitc, 383, 300, jj>2 Argcntitc, 31, 78, 7, 497 Ante, 04
Arsenic, 40, $a, 407 Arscnohtc, 111, 152, 511 Araenopyri te, i or , ; 1 1 , 49 7 Asbestos, 386, 398 Atatamite, 144, 504 Augite, 365, 3?o, 374, 500, 501, 503,
504, 506, 507
Autumte, 2
Aventurme, 164
Axinite, j, 506, 507, 509, 510, 512,
Azunte, 231,,504
Babingtonite, 365, 380 506 Baddeleyitc, 167 Baltimonte, 398 Barbierite, 408, 413 Baricalcite, 223, 231 Bartte, 238,?, 5 Barium orthodase, 4x6 Barytocalcite, 931 Bauxite, 186, 502, 503, 5x2
Index Of Minerals
Beaumontite, 447
Beryl, 359, 507, 509, 511, $12
Beryllomte, 263, 512
Biotite, 349, 500, 501, 504, 50$, 506
Bismuth, 49, 50, 500
Bismuthimte, 72, ?/, 497
Blende, 87
Bloodstone, 164
Blue beryl, 361
Bobiente, 281
Bog iron, 185
Boracite, 207, 210, 506, 507, 509, 510, 512
Borax, 207, 209, 221, 511
Bormte, 129, 130, 497
Bort, 39
Bortz, 39
Boumomte, 117, 120, 497
Brandisite, 426
Braumte, 204, 497, 498
Brazilian chrysolite, 436
Brazilian emerald, 436
Brazilian pebble, 164
Brazilian sapphire, 436
Breithauptite, 94, P5 499
Brittle micas, 426
Brochantite, 243 245, 504
BrQggente, 298
Bromargynte, 137
Bromate, 231
Bronzite, 305, 505, 507
Brookite, 167, 176, 498, 499, S°o, sor,
Brown clay ironstone, 185 Brown hematite, 183 Brucite, 2, 12, 181, 506, 510, 511 Brushite, 292 Brucklandite, 329 Bustamite, 365, 380, 508 Bytowmte, 417, 418
Cabrente, 281 Cacholong, 180 Cairngorm stone, 164 Calamine, 396, 505, 506, 510, 512 Calavente, 114, 497, 499, 500 504, 505, 507, 508, 509, sic, $n Cahformte, 433, 434, 512 Cancrimte, 315, 507, 508, 510, 512
Carbonado, 39 Carnalhtc, //j, CurnegiciU>T 4. Carnclun, 164 (\irnotite, 2X8, j Cassitente, if>7,
, 508, <yoo, o, //A1
501,
Si*
Orussitts .M? j-7, U' (Ceylon i tt*t 100, /y
ethnic anthitv, 240, Clmltwlonv, 150, C'haicmhc, ,V;, 07 ("haltotrhhitf, I.J.H C'haltopvnte, ttd, i Jt>, ; ?f, 407 (*hathamitcs to.S Chert, xMo ChiuHtolttc, 33 r Chile saltjwU'r, jto Chloanthitf, iot( 407 Chlorupatitts Chlonwtrolitc, ,ws,
Chlromt'luitt% 377
Chlrophanct 140
ChlorophylliUs 4$)
Chlorapmcl, 106
Chomlrotiitts 3,p, ,?nt 5off 501;, si
Chrome diopside, j;a
Chrome , 17
Chrysolite, ?J
Chrysolite, Brazilian, 436
Chryaoprase, 164
Chrysotile, 398, 505, 506, soy, 511
Cinnabar, 22, $
Citrine, 164
Claudetitc, 151,
Clausthahte, 79, 497
Clay, 405
Index Of Minkhals
Cleveitc, 298
Clmochlore, 420, 430
Clmohumitc, 332
Clmosoibitc, 1st)
Clmtomte, 50$,
Cobdltitc, ioi, /oft, 407
Colenumte, 207, 2r)<S', 512
Columbitc, 2p?, 497, 408, 400
Coloradoitc, 07
Comptomte, 455
Cookeite, 3<n
Copper, 31, v, 5*i Mi W)
Copper pyrites, / ?/
Cordicnte, ;*V, 509, $10, ;i2
CorundophylHte, *po
507*508. 500,510,511,512 Covelhte, 96, 407 Outotahtc, rV Crocidohtc, 383, 30 r, ?w? 04 Gratoittt,aif 3,502, 503 Cryolite, 3, /v?> 508, 5H Cryophyllite, 353 CumatoHtcs 370 Cummingtomte, 382, ?.S>, <J07 Cuprotungstite, 254 Cymatohte, 379 Cyprine, 434
l)amourite, 37
Danburite, 31, 320, w, 506, 509, 5x2
Belessite, 432
Delvauxite, 276
Demantoul, 3x2
Diallage, 374
Diamond, ?;, 505, 506, <;i2
Diaspore, i#g, /pw, JoO, 507, 509, 512
Dichroite,
Diopsidc, 365, 370, 505, 507, 508,
510, 512
Dioptasc, jw, 504 Dipyr, 434 Disthene, 319, jpj Dog-tooth spur, 214, 215 Dolomite, 504, 505. 508, 509, 512 Domeykitc, 7?, 497 Dry-bont ore, 221
Dufremte, 274, 275, 498, 504 IXtfrenoybite, 122 Dumortieritc, ??#, 04, 512 ])yskrasite 77, 7$, 500 Dysluite, 196
Edenitc, 388
Klcctrum, 50
KleolUc, ?/;
Emerald, 61
Kmewld, Brazilian, 46
Kmerald, Oriental, 156
Emery, 15-;,
Emirate, n6, 122, /2?, 407
Enbtatite, 5, sos, S07. 512
Kpidote, 3J6, 7.7, 505, 500, $ob,
500, Sio
Kpsomite, 246, 249, 511 Erythnte, 281, J.V>, 50 j Kssomtc, 30(), j; i Kucryptite, 313 Eukante, 79
Fahlunite, 439
Fairy stones, n8
liaise topa/, J(>4
Fanmtmitr, I*M
Fassaite, 374
Kiyalite, 2, 302, 507
Feldspars, 408
Ferbente, s$N, 501
Fergiwmitc, 293, 498
Fibrohte, ?3?, 322
Fl&hesd'timour, 174
Flint, 165, 180
Flos fern, 223
Fluorapattte, 266
Huorfte, z?v, 504, SOS* 506, S07 500,
510,511,512 Fool's gold, 104 Fotttente, 302, ,?o ?, 507 Fowlerite, 365, Vi, soft Franklmite, 190, 195, 196, , 497>
4Qq
Frernontite, 274 FuthUe, 357
GadoHnite, 334, #5 500, 506, 507 Gahnite, 196
Index Of Minki5Als
, 50".
Galena, 32, 79, 81, 407 Garnet, 308, 312, 501,
510, 512
Garniente, 400, 504, $oto Gaylussite, 234, 235, 511 Gcdnte,382, #3, 507, Genthite, 400 Gcrsdorflitc, 101
Gibbsitc, i&?, 50, 5°8 W, -Jio, <ju Gigantohtc, 439 Girasol, 180 Glaiw, 100
Glauberite, 2jrf, 507, 508, <jo), 511 Glauber salt, 246 Glauiodot, 101 Glauconilc, 442, 504, 506 Glaucophane, 383, w, 504, 5*o Gocthitc, 2, 4, 37, 4<,A 400. $00,
501, 502, 50* Gold, 19, 52, 53, jtf, 499 Gold amalgam, 53 Golden beryl, 361 Graphite, 37, 44, 479, 501 Graphitite, 45 Greenahte, 44 ?
Greenovitc, 465 Greensand, 442 Grossularite, 300, ?/ 1 Grttnente, 382, .7, 507* 51 1 Guano, 268 Gypsite, 248
Halloysite, 404 Hancockite,*326 Hanksite, 251,5509,511 Harmotomc, 445, 449, 505, 508, 509, 512 Hauerite, 101 Hausmannite, 304, 498 Hatiymte, 339, 340, 341, 5x0 Haydemte, 457 Hedenbcrgite, 365, &z Heliotrope, 164
Hematite, 17, 37, xSx, *S2, i$3> 498, 499) 503
iihrous,
, / VV Hornsttmt', 16 Morsi* Ili'sb on*, /
Hulnuritc, .A1, 408, S04, 5o;, soS, flumitv, Hussikitc*. fto ', i So
itt1,
500,
r, at6
Infuwdul earth, i
lodyritf, 137 lolite, jtf
Iridium, 52, 63, 66, 501 Iridogmmc, 7, 500 Iron, 52, 63, 6$, 497 Iron-platinum, 6$
JacobsUe, 196
Jm, 377
Jdeite, 365, ,377, 507, 51 a
Jalpdte, 78
Jamesonit*, iw, 497
sou,
504,
Index Of Mineral
Jasper, 165 Jeffersonite, 373
Kamite, 2$r, 507, <?o8, 509, 911
Kahnite, 251
Kahophthte, ?n
Kdolimte, 40*, A SW, 506, 508, 500,
Kaolin, 404
Katofonte, 388, 390, 39 r Kiescntc, , 5 1 1 Korvnitt*, 101 KottmKitc, 281 Kreittomtc, igft Krennente, 1 14 Kunzite, 370 Kyamtc, 419, ,w?, *?to, 512
Labratloritf, 417, ;/V, 504, 507 Lake (leortfe iliamonds, 104 Ltipis la/uli,
SfPt S" La/ulite, 274, .75, 510
Lead, si> S,i. tot 407 littodhiltittt, 251, 252, -505, Lcpjclohte, 353, w, 507, Lepidotnclanc% 340, 350 Leptochlorites, 428, .p, 506 Leucite, jfo, 512 Limestone, 216 Limonite, ai, 32 33, /. w%, 499.
Lintonite, 456
Lithiophihte, 262, 505, 07, 5x0 Lithographic stone, 210 Ldllingite, 101, //,?, 497 Lucinite, 284
Magnesioferrite, 196
Magnesite, 313, 504, 505, 509, 512
Magnetic pyrites, <tf , 497
Magnetite, 2, 25, 37, 190, 195, 196,
*P#, 497 Magnofernte, Malachite, 12, 30, 31, 212, 231, 232, 504
Malocolite, 372 Mtinganapatite, 268 Mdngiinitc, 4Q.H, 499 Mannopcctolitr, 370
Marbles 216
Martabite, 101, my, 407
Marganto, ??jf 507, 509, ;ri
Marit&litc, Jj
Martitc, i?4
Masonite, 428
Meerschaum, 397, t/or, 511
Meumite, ./- ?
Molaconite, 407, 501
Melamte, 309, vs
MeUntentc, 346, 240, 506, 511
Mercury, 52, 53 62
Meroxcne, 349, ,??f>
Metacmnabaritc, 97, too, 497
Mexican onyc, 216
Mua, 348
first order, 348
second order, 348
amber, 350
MuRKlmt'i 408, 409, 4W Munxlme perthite, 415 Milky quartz, 164 Milleritc, t)4 P5 497 Miitietite, 260, 271, 505, 512 Mirabilite, 246, 511 Mhpickel, xn Muzonite, 423 Monazite, 505, 508, 5x0 Montebrasite, 274 Monticelhte, 30, 302 Montmorillonite, 404 Moonstone, 415
Nail-head spar, 2141 215
Nakrite, 404
Natrohte, 446,
Natron, 234, ,55
Naurnanmte, 78
Neotype, 223
Nepheline, 313, 314
'Nephehte, 3x3, 314, S°$ So7 So8, 510,
Nephrite, 387 Niccohte, 04, OS* 497 Niter, 206, jn Nivemte, 208 Nosean, 339, 340, 341
Ochcr, 185 Ocher?rcd, i<;4
yellow, 185 Octahedntc, 167, 176 Ohgoclase, 417, 418 Ohvemte, 274,77, 504 Ohvme, 302, 303, sob, 5*° Omphacitc, 374 Onofnte, 97 Onyx, 165
Onyx, Mexican, 216
precious, 180
fire, 180
common, 180 Ophicalcite, 399 Orangeite, 3x9 Onental amethyst, 156
emerald, 156
topaz, 156 Orpiment, 7*, 503
Orthochlorite, 428, 4*0, 506, 50Q,
Osmiridium, 6*7, 500 Osmium, 52, 63 Osteolite, 268 Ottrebte, 428
Palladium, 63, 66, 500
Panderxnite, 309
Paragomte, 354, 358, 511
Parasepiohte, 401
Parasite, 2x0
Pargasite, 388
Patronite, 373
Pearccit j, 497
Pearlspar, 229
Pectolite, 364, 365, 367, 36$, 51
Penninite, 42$
Pentlandite, 87, oa, 497, 49
Pcndot of Ceylon, 37, 436
Perovslute, 461, 500, 50?, 504, 506, 509
Index Of Minhkalh
, 445, //,, tins, MHU
509,
Iliosphontr,
, 507
Platin indium, Plutimim, Platinum u<m, IHttttnentc, tH PIronantrt wo,
Polyiwhtc,
, 40?
Potash tlim IHW* 417,491 IVuHc, 164
Pricdfe* 30 Prochlorkc,
PKcudowalkMttmttr, Pwlomciane, iA'A\ 4tj7, 48, 501
19, at, s, wi,
magndic, 92, 4<J7 Pyro!uSte, 167 17, 407 PyromarphiUf, a0 506,500,511 Pyropc, 309, j;/ Pyrophyliite, 403, 4°*
S"
Pyroxenes, 363, 364 PyrrhoUte, oo, ftf, 497
$04,
Index Of Minerals
', 17, 28, 32, T1Q, 505, 50, S07,
nulk>, 104 rost, 164 smoky, 164
Rabenghmmer, 353
Rammelsbergite, 101
Realgar, 5°3
Red other, 154
Rhinestone,
Rhodium, 03
Rhodochrosite, 13, 505, 506, 507,
508,500,51-* Rhodolite, 311
Rhodonite, 3615, $<J, 508, 510 Riebeckite, 383, 390, #J Rock crystal, 164 RocL gynpum, 48 Rock salt, /,?/, 281 Roepperite, 30 j
Rone quart/, 164 Ru belli te, 435 Ruby, 156
Ruby , Ruthenium, 63
Rutik, 167, 168, ///, 408, 4Q9, 500,
Hufloritc, 101
Sugenite, 164
Sahlite, 365, 373
Saltpeter, ao,
Sjimarnkite, 48, 490
Sanidmc, 415
Sapphire, 15
Sapphire, Brazilian, 436
Sardonyx, 165
Satinftpar, si6, 225, 348
Sauafturtte, 4a, 422
Mcapdite, -w, 507* 508, 510, sn, 513
Scheelite, 354, 507, 508, 509, $12
Schoilomite, 300, 3x2
Siolocitc, 446, 452 ', 12
Selcnitc, 248
Selenium, 47
Scnarmontitc, i;r, 752, 50?, ;o7, 511
SeruiU', 357
Serpenline, 307, W, 428, 504, 05, $06,
1508, 500 Sidente, 21, 32, 37, 213, zig} 498, 499,
SOT, w, W, 505,512 Siliceous sinter, :8o Sillimanitc, 319, 320, pr, 506, 507, 512 Silver, 3 1, 52, ?3,5?, 501 Siher amalgam, 53, Sinter, siliceous, 180 Skonxhte, 281 501, 506, 510 Smaltite, toi, /r>7, 407 SiiLiragditc, ,?<V<V, 389 Smithsonite, 213, asr, 505, 507, 510, 512 Smoky quartz, 164 Soapstone, 402 Soda, 212, a?/, 511 Soda alum, 251
Socialite, 339, &o9 508, 5x0, 512 Soda niter, 205, 511 Specular hematite, 154 Sperryhte, 101, ioA\ 497 Spessartitc, 309, 312 Sphalerite, 7, 498, 499, 500, 501, 02,
503, 504* 505, 508, 509 Sphene, 461, 464 Spinel, 2, 195, ig6> 498, 500, 501, $02,
503, 505, S07i So8, 509, 50.
5"
Spodumene, 365, 57*, $07, 508, 511, 512 StasHfurtite, 210 Staurohte, 407 505. 506 Stemmarkite, 404 Steplmmtc, 479 StJbnite, 22, 69, 7*1 497 Stilbite, 445, 45<VSO$, 506, 507, 500, Stotate, 254, 505, 506, 508, sn Stream tin, 170 Stromeyerite, 84, 86) 497, 500 Strontianile, 313, 223, 225, 505, 506, 509,
5"
Sulphur, 17, ai, 3X1 47, 503, $09 Suns tone, 415
Index Of M1Nkkaij4
Sylvamte, 113, 114* SOQ> 5°* Sylvite, 134, /3ft 508, 509, Symplesite, 281
Talc, 401, 509,
Tantahte, 293, 497, 49&
Tennantite, 124, 126, 497
Tenonte, 2, jp
Tephroite, 302, 305, 506, 508
Tetradynute, 75, 497, 500
Tetrahednte, 124, 126, 4Q7, 408, 400
Thenardite, 237, $o8,*str
Thomsomte, 446, 45?, $0$, W, ;o8
Thorite, 316, jrp, 408, 501, J02, 503 Thuhtc, 326, 327 Thunngite, 432 Tiemannite, 97 Tiger's-eye, 393
Tin, 52
Tinstone, 170
Titamte, 464, 300, sot, $04, $05, 507,
508, 510
Titanohvme, 302 Titanomorphite, 465 Topaz, 319, 320, 322, 507, 508, 509,
510,511,512 false, 164 Oriental, 156 Topazojlite, 312 Torbermte, 288, 389, 504 Touchstone, 165 Tourmaline, 434, 501, 505, 506, 507,
Travertine, 2x6 Tremohte, 382', 385, 3, 508, S"
Tridymite, 158 Tnphyhte, 2 fa, 507, 510
Tripohte, 180, 505, 509, 512 Trona, 234, 235, 509, 511 Troostte, jotf, 506, 507, 509 Turquoise, p, 504, 507, 510
Ullmanite, xox tlraJite, 374, 39 T7ramte, 286, 288
SOJ, 505 Urancx irritt\ JM8
) 407,
Uvaruvile, 30*), J/ f,
Valentmito, 15 r, /?J, 511 Vanothnite, 3W, .71, 50$, 50jf
W, 511
Vunscitts J8i, jV;, 50/1 Vtittl-untique, Vcsuvianito, ?j, jjo<>, 507, 50*), 510 Vitriol, 4() Viviamte, -f.V;, 504, $otf 510, 511
Wavellite, 380, 504, 505, $06.
5to, 51 Werneritc, 424 White beryl, t$fti Whitncyite, 78
Willemite, j/w5 joTj, 508, 510, 51 j Withamitc, 3*) Witheritc, 23, wtf, 512 Wolfachlcs tot Wolframite, 54, 497.
50 r, soa Wollastonite, 364, 365, 367,
Wood tin, 170 Wulfenlte, 354, a$jr> 503, SoS
Wurtzite, $K>, 498
Xanthophyliite, 426
Yellow ocher, 185 Yttrotantalite, 5p5, 504, 505
ZeollteB, 445
Zeunedte, 288
Zbnwaldlte, J5t, 305, $o6 507,
Zoisite, M 506, 507*
500,
(x)