Dana's manual of mineralogy : for the student of elementary mineralogy, the mining engineer, the geologist, the prospector, the collector, etc.

Dana, James Dwight · 1929 · Historical

x, 476 p., [9] leaves of plates : 19 cm

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

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Manual Of Mineralogy

Series Of Mineralogies

System of Mineralogy

Sixth edition, entirely rewritten. With Appendices I and II, completing the work to 1909, 1333 pages and more than 1400 illustrations; and with the Third Appendix, by William E. Ford, Assistant Professor of Mineralogy in Sheffield Sci entific School of Yale University, completing the work to 1915, 87 pages. Complete volume, by 10, half leather.

A Text-book of Mineralogy

With an extended Treatise on Crystallography and Physical Mineralogy. By Edward Salisbury Dana, Professor Emeri tus of Physics and Curator of Mineralogy, Yale University. Third edition, rewritten and enlarged. By William E. Ford (1922). 720 pages, 6 by 9,, 1050 figures. Cloth.

Minerals, and How to Study Them

A book for beginners in Mineralogy. By Prof. E. S. Dana. Second Edition. 380 pages, 5 by 7j, 319 figures. Cloth.

Manual of Mineralogy

For the Student of Elementary Mineralogy, the Mining Engineer, the Geologist, the Prospector, the Collector, etc. Fourteenth edition, entirely revised and rewritten, by Wil liam E. Ford. 476 pages, 5 by j\, 360 figures, and 10 plates. Cloth, or flexible binding.

Dana'S Manual Of Mineralogy

FOR THE STUDENT OF ELEMENTARY MINER ALOGY, THE MINING ENGINEER, THE GEOLOGIST, THE PROSPECTOR,

The Collector, Etc.

By

William E. Ford

Professor of Mineralogy in the Sheffield Scientific School of Yale University

Fourteenth Edition, Total Issue, Forty-One Thousand

New York

JOHN WILEY & SONS, Inc. London: CHAPMAN & HALL, Limited

Copyright, 1912, 1929, By EDWARD S. DANA and WILLIAM E. FORD

Copyright, 1912, 1929, in Great Britain

Printing

T. H. Gilson Co. Boston

Printed in U. S. A.

Composition and Plates Binding

Technical Composition Co. Stanhope Bindery

Cambridge Boston

Preface To The Fourteenth Edition

It is now more than sixteen years since the last revision of this book. It seemed wise, therefore, to reexamine it and to make such changes as the lapse of time had rendered desirable. These changes consist in the addition of certain short paragraphs that serve to indicate the important recent developments in the science, especi ally in the section on crystallography. Minor changes of phrase ology have been made throughout the book in order to render the subject matter simpler and clearer. In the section devoted to the description of minerals the paragraphs dealing with mode of origin and localities of occurrence have been thoroughly revised. The genesis of the minerals has been given in greater detail and in the case of mineral localities only those of outstanding importance are now given. Appendix II, Mineral Statistics, has been brought up to date.

Sheffield Scientific School of Yale University,

New Haven, Conn., December, 1928.

Preface To The Thirteenth Edition

The "Manual of Mineralogy" was first published by James Dwight Dana in 1848. A second edition was printed in 1850 and a "New Edition," which had been revised and enlarged, was published in 1857. The book was rearranged and rewritten for the third edition which appeared in 1878. This edition included an extensive chapter on rocks, and the title of the book was changed to "Manual of Mineralogy and Petrography." The fourth and last revision was published in 1887. Since that time the book has been frequently reprinted, so that the last edition was the twelfth. But it is now twenty-five years since the last revision of the text. Believing that the Manual has amply proved its usefulness, and with the desire of keeping the series of the Dana Mineralogies complete, Professor Edward S. Dana asked the author to prepare a new and revised edition.

It was found that it was desirable to rewrite the book, and consequently, as far as the text and figures are concerned, this present edition is almost wholly new. The scope and character of the book, however, have been kept as nearly as possible the same. The book has been primarily designed to fill the ordinary needs of the elementary student of Mineralogy, the mining engineer, the geologist and the practical man who may be interested in the sub ject. It has been made brief and direct and the treatment has been as untechnical as possible.

The chapter on Petrography has been omitted and only a brief and general description of the various important rock types given. This change was made in view of the fact that since 1887 the sub ject of Petrography has had so large a development as to render impossible its adequate treatment in a single chapter. Moreover, several elementary books on the subject, notably "Rocks and Rock Minerals" by L. V. Pirsson, are now available. Because of this, the title has been changed again to its original form and the book is to be known in the future as "Dana's Manual of Mineralogy."

Preface

The order adopted in the description of species has been changed to that of the chemical classification as used in the System of Mineralogy. It was felt that this was, on the whole, the most logical and useful arrangement. Following the description of the individual species, however, various tables are given, among them one in which the minerals are grouped according to their chief element. After each such list a general description of the associa tion and occurrence of the minerals which it contains is given. Statistics of mineral production, etc., are given in Appendix II. It is intended by frequent revision of this portion of the book to keep the figures reasonably up to date.

The author has made free use of many sources in the prepara tion of the book. He is especially indebted to the sixth edition of "Dana's System of Mineralogy" and the "Text Book of Miner alogy" by E. S. Dana, to the "Brush-Penfield Determinative Mineralogy and Blowpipe Analysis" and to "Rocks and Rock Minerals" by L. V. Pirsson. He acknowledges gratefully the constant advice and criticism of Professor Edward S. Dana.

Sheffield Scientific School of Yale University,

New Haven, Conn., June, 1912.

Introduction

Minerals are the materials of which the earth's crust consists and are therefore among the most common objects of daily obser vation. A-jrdneral may be defined as a naturally occurring sub stance haying a definite and uniform cheiil .sit.inn with corresponding characteristic .physical propprtioa This eliminates all artificial products of the laboratory which mav conform to the last part of the definition. It also eliminates all natural products of organic agencies, since they will not show the uniform chemical and physical characters demanded of a mineral.

In the form of rocks, minerals make up the solid matter of the earth's crust. But in the great majority of cases a rock is not made up of a single mineral, but is a more or less heterogeneous aggregate of several different species. A few rocks, like limestone and quartzite, consist of but one mineral in a more or less pure state. In addition to occurring as essential and integral parts of rocks, minerals are found distributed through them in a scattered way, or in veins and cavities. Water is a mineral, but generally in an impure state from the presence of other minerals in solution. The atmosphere and all gaseous materials set free in volcanic and other regions are mineral in nature.

Characters of Minerals

1. Minerals, as previously stated, have a definite chemical composition. This composition, as determined by chemical analysis, serves largely to define and distinguish the species. Owing to difference in composition, minerals exhibit great differ ences when subjected to the action of various chemical reagents, and these peculiarities are a means of determining the kind of mineral under examination in any case. The department of the science treating of the composition of minerals and their chemical reactions is termed Chemical Mineralogy.

2. Each mineral, with few exceptions, has its definite form, by

"W

Introduction

which, when in good specimens, it may be known. These forms are cubes, prisms, pyramids, etc. They are included under plane surfaces arranged in symmetrical order, according to mathematical law. These forms are called crystals. Besides these outward forms there is also a distinctive internal structure for each species. The facts of this branch of the science come under the head of Crystallographic Mineralogy.

3. Minerals differ in hardness, from talc at one end of the scale to the diamond at the other. Minerals differ in specific gravity, and this character, like hardness, is a most important means of distinguishing species. Minerals differ in color, transparency, luster and other optical properties. The facts and principles relating to the above characters and others of a similar nature are included in the department of Physical Mineralogy.

4. The detailed descriptions of individual mineral species, including their chemical, crystallographic and general physical characters, together with their occurrence, associations, uses, etc., are included under the division known as Descriptive Mineralogy.

5. Lastly, the discussion of the methods that are used for identi fying minerals forms the division known as Determinative Mineral ogy-

These different branches of the subject are taken up in this book in the following order: I. Crystallographic Mineralogy; II. Physical Mineralogy; III. Chemical Mineralogy; IV. De scriptive Mineralogy; V. Determinative Mineralogy.

Table Of Contents

Page

Introduction . vii

I. Crystallography

Introduction . 1

Symmetry . 10

Crystal Notation . 12

Definitions of Various Terms . 15

Isometric Sy'stem . 19

Tetragonal System . 35

Hexagonal System . 41

Orthorhombic System . 51

Monoclinic System . 56

Triclinic System . 61

Ii. General Physical Properties Of Minerals

Structure of Minerals . 64

Cleavage, Parting and Fracture . 66

Hardness of Minerals . 67

Tenacity of Minerals . 68

Specific Gravity of Minerals . 69

Properties Depending upon Light

Luster . 72

Color of Minerals . 74

Refraction of Light in Minerals . 75

Double Refraction in Minerals . 78

Pyroelectricity . 79

Iii. Chemical Mineralogy

Chemical Groups . 81

Derivation of a Chemical Formula . 82

Calculation of Percentage Composition . 83

Isomorphism . 84

Isomorphous Groups . 86

Dimorphism, Treuorphism, etc . 87

Instruments, Reagents and Methods of Testing . 88

Tests for the Elements . 102

Contents

17. Descriptive Mineralogy

Page

Description of Species . 124

Lists of Minerals Arranged According to Elements 326

Occurrence and Association of Minerals

Rocks and Rock-making Minerals . 345

Pegmatite Dikes and Veins . 361

Contact Metamorphic Minerals . 363

Veins and Vein Minerals . 364

Lists of Minerals Arranged According to Systems of Crystallization . 370

V. Determinative Mineralogy

Introduction . 380

Determinative Tables . 385

Index to Determinative Tables . 450

Appendix I. List of Minerals for a Collection . 452

Appendix II. Mineral Statistics . 453

Manual Of Mineralogy

I. Crystallography

I. Introduction

The great majority of our minerals, when the conditions of formation are favorable, occur in definite and characteristic geometrical forms which are known as crystals. To gain a com prehensive knowledge of the laws which govern the shape and character of crystals is a very important part of the study of mineralogy. This division of the subject is called crystallog raphy. It forms almost a separate science in itself, and to ade quately and exhaustively discuss it would require a volume much larger than the present one. In the following section, however, the attempt will be made to present the elements of crystallography in a brief and simple manner and at least to introduce the reader to the more essential facts and principles of the subject.

A crystal has been defined as follows : A crystal is a body which by tin operation of molecular affinity has assumed a definite internal structure with the form of a regular solid inclosed by a certain num ber of plane surfaces arranged according to the laws of symmetry.* This is a very compact definition and several pages will be devoted to its discussion.

A better idea of the fundamental laws of crystallography will be obtained by first considering the three prominent modes of crystallization. Crystals are formed by crystallization either (1) from a solution, (2) from fusion, or (3) from a vapor. The first case, that of crystallization from solution, is the most familiar to our ordinary experience. Take for example a water solution containing sodium chloride (common salt). Suppose that by evaporation the water is slowly driven off. The solution will,

Century Dictionary.

Manual Of Mineralogy

under these conditions, gradually contain more and more salt per unit volume, and ultimately the point will be reached where the amount of water present can no longer hold all of the salt in solu tion, and this must begin to precipitate out. In other words, part of the sodium chloride, which has up to this point been held in a state of solution by the water, now assumes a solid form. If the conditions are so arranged that the evaporation of the water goes on very slowly, the separation of the salt in solid form will progress equally slowly and definite crystals will result. The particles of sodium chloride as they separate from the solution will by the laws of molecular attraction group themselves together and gradually build up a definitely shaped solid which we call a crystal. Crystals can also be formed from solution by lowering the temperature or pressure of the solution. Hot water will dissolve much more salt, for instance, than cold, and if a hot solution is allowed to cool, a point will be reached where the solution becomes supersaturated for its temperature and salt will crystallize out. Again, the higher the pressure to which water is subjected the more salt it can hold in solution. So with the lowering of the pressure of a saturated solution supersaturation will result and crystals form. Therefore,

. in general,, crystalsjmay form from a solution by the evaporation of thejsqlvent, by the lowering of the temperature or by a decrease in pressure.

A crystal is formed from a fused mass in much the same way as from a solution. The most familiar example of crystallization from fusion is the formation of ice crystals when water freezes. While we do not ordinarily consider it in this way, water is fused ice. When the temperature is sufficiently lowered the water can no longer remain liquid, and it becomes solid by crystallization into ice. The particles of water which were free to move in any direc tion in the liquid now become fixed in their position, and by the laws of molecular attraction arrange themselves in a definite order and built up a solid crystalline mass. The formation of igneous rocks from molten lavas, while more complicated, is similar to the freezing of water. In the fluid lava we have many elements in a dissociated state. As the lava cools these elements gradually group themselves into different mineral molecules, which gather

Introduction

together and slowly crystallize to form the mineral particles of the resulting solid rock.

The third mode of crystal formation, that in which the crystals are produced from a vapor, is less common than the other two described above. The principles that underlie the crystallization are much the same. The dissociated chemical atoms through the cooling of the gas are brought closer together until they at last form a solid with a definite crystal structure. An example of this mode of crystal formation is seen in the formation of sulphur crys tals about the mouths of fumaroles in volcanic regions, where they have been crystallized from sulphur-bearing vapors.

The most fundamental and important fact concerning crystals is that they possess a definite internal structure. A crystal is to be conceived as made up of an almost infinite number of exces sively minute chemical particles which have a regular arrange ment and relation to each other and form, as it were, a crystal network. It has been possible recently to determine in many cases, not only the kind of atomic structure that a given substance possesses, but to place in that structure the positions of the various kinds of atoms present. The unit of structure must be considered as the smallest portion of the substance that still possesses its characteristic properties. This can never be as small as an indi vidual atom since the relations of the atoms to each other are important factors in determining the characters of the substance. It must therefore consist of a group of atoms sufficiently large to show all the properties of structure of the crystal, or a chemical molecule, or a group of molecules. For instance in quartz the structural unit has been shown to consist of three molecules of Si02. Any smaller subdivision would not have the properties of the mineral. There are many proofs that a crystal does possess a definite internal structure but the following are the most important.

Cleavage. Many minerals when fractured break with definite and smooth flat surfaces which are known as cleavage planes. Common salt, halite, for instance, cleaves in three different planes which are at right angles to each other. It is said, therefore, to have a cubic cleavage. When it crystallizes it usually shows cubic forms also. The planes of cleavage are found to be always

Manual Of Mineralogy

parallel to the natural cubic crystal faces. If the internal struc ture of halite was heterogeneous, the fact that it always shows this cubical cleavage would be inexplicable. It can only be explained by assuming some definite internal arrangement which permits and controls such a cleavage.

Optical Properties. All transparent crystals have definite effects upon the light which passes through them. Many of them further produce changes in the character of the light which cannot be accounted for except through the constraining influence of the internal structure of the mineral. Take the case of calcite as an example. In general, if you look at an object through a clear block of calcite you will observe a double image. The mineral, in other words, has the power of doubly refracting light. Further, it can be proved that each of the two rays into which calcite breaks up light has a definite plane of vibration, i.e., each ray is polarized. A piece of glass similar in shape to the calcite block would not have produced these effects, because the internal structure of glass is heterogeneous, while that of calcite is definite and regular.

Regular and Constant Outward Form. If a series of objects all having the same shape and size are grouped together accord ing to some regular arrangement, the resulting mass will have a definite form which will bear a strict relationship to the character of the individual objects and the law which was followed in as sembling them. As a simple illustration, consider an ordinary pile of bricks. If each individual brick is exactly like every other in size and all of them are piled together according to a regular plan, the shape of the resulting mass will depend directly upon the shape of the individual bricks and the law which governed their arrange ment. Figures A and B, Plate I, are reproductions from photo graphs of models which are built up solidly of small steel balls. All of the constituent particles of each model are exactly alike in shape and size, and they have been piled together according to a regular arrangement. The result has been, as is shown in the figures, to produce regularly and definitely shaped solids. If therefore a regular arrangement of uniform particles produces a solid with a definite shape, the converse proposition must be true. If we have a mineral which occurs in certain characteristic and uniformly

Plate I.

A. Cube.

B. Octahedron. Models made of Steel Balia.

Introduction

shaped crystals (halite, for example, in cubes) , it must follow that this could only be accomplished through the mineral possessing a regular internal structure.

X-Ray Evidence of Regular Structure. In 1912, while attempting to prove a similarity in character between the vibrations of X-rays and light, Dr. Laue conceived the idea of using the or dered arrangement of the atoms in a crystal as a "diffraction grat ing" for their analysis. He argued that if the distances between the parallel atomic layers in the crystal net-work were of the same order as the wave lengths of the X-rays that diffraction of the X- rays should result. Aided by Friedrich and Knipping the experi ment was tried of placing a photographic plate behind a crystal section which in turn lay in the path of a beam of X-rays, with the result that not only did the developed plate show a dark spot in its center where the direct pencil of X-rays had hit it but it also showed a large number of smaller spots arranged around the center in a regular geometrical pattern. This pattern was formed by the interference of waves which had been diffracted in different direc tions by the atomic structure of the crystal. In addition to a new method of studying the character of X-rays this experiment gave a most important means for the study of the internal structure of crystals. Figure 1 gives a diagrammatic representation of a Laue photograph obtained by directing a beam of X-rays normal to a cube face of a crystal of halite, sodium chloride. The dark spots indicate the relative position in the crystal net-work of various atomic planes parallel to possible crystal faces and their arrange ment indicates the symmetry of the crystal.

Other important methods have since been devised for studying crystal structure by means of X-rays. Among these is one which involves the reflection of the X-rays from the different atomic planes of the crystal. In general the rays reflected from the suc cessive planes would be in different phases of vibration and so would tend to interfere and neutralize each other. But with a certain angle of incidence and reflection it would happen that the different reflected rays would possess on emergence from the crystal the same phase of vibration and would therefore reinforce each other. This angle would vary with the wave length of the X-ray

Manual Of Mineralogy

Fig. l.

Fig. 2.

Introduction

and with the spacing between the atomic layers of the crystal. By the use of a special X-ray spectrometer the angles at which these reflections take place can be accurately measured. By this method the distances between the atomic layers of the crystal can be determined. Still another method should be mentioned. This is the so-called "powder method," in which a tube of powdered mate rial is subjected to a beam of X-rays and the position of the diffracted rays shown by lines produced on a photographic film which has been placed around the tube in a circular arc. Since the powder will contain particles in all possible crystal orientations the dif fracted rays indicate the position of all the different atomic planes in the crystal structure.

By these various methods it has been possible in many cases, particularly of the simpler compounds, to definitely determine the crystal structure. As an example the case of halite mav.be-cited. We now know that the sodium and chlorine atoms are arranged in the crystal net-work as shown inFig. 2. We also know with precision the distances between the atomic layers of its crystals.

The Outward Crystal Form May Be Varied with the Same Internal Crystalline Structure. There may be several different limiting forms possible upon crystals of the same mineral. Galena, PbS, for example, usually crystallizes in the form of a cube, but it also at times shows octahedral crystals. The internal structure of galena is constant, but both the cube and octahedron are forms that conform to that structure. The models shown on Plate I illustrate this point. Both are built up of similar particles and their ar rangement is the same in each case. In one, however, (Fig. A), the planes of a cube, and in the other (Fig. B) the planes of an octahe dron, limit the figure.

With the same internal structure there arey however, only a certain number of possible planes which can serve to limit a crystal. And it is to be noted, moreover, that of these possible planes there are only a comparatively few which commonly occur. The posi-_ tions of the faces of_a crystal are determined hv those directions in which on account of the internal structure a large number of the individual mineral units lie. And those planes which include the greater number of units are the ones most commonly found as faces

Manual Of Mineralogy

upon the crystals. Consider Fig. 3, which might represent one layer of units in a certain crystal network. These units are equally spaced from each other and have a rectilinear arrangement. It will be observed that there are several possible lines through this network that include a greater or less number of units. These lines would represent the cutting direction through this network of

certain possible crystal planes; and it would be found that of these possible planes those which include the larger number of units, like those cutting along the lines A-B and A-C, would be the more common in occurrence.

Law of the Constancy of Interfacial Angles. Since the internal structure of any mineral is always constant, and since the possible crystal faces of that mineral have a definite relationship to that structure, it follows that the faces must have also a definite relationship to each other. This fact may be stated as follows: The angles between two similar faces on the same substame. are always the same. Figure 3 will also illustrate this point. The face which cuts the network along the line A-C must make an angle of 45 degrees with the face which cuts along the line A-B, etc. This law is the most fundamental and important in the science of crystallography. It frequently enables one to identify a mineral by the measurement of the interfacial angles on its crystals. A mineral may be found in crystals of widely varying shapes and sizes, but the angle between two similar faces will always be the same.

An important part of the study of crystallography consists in the measuring and classifying of the interfacial angles on the crys tals of all minerals. These measurements are accomplished by means of instruments known as goniometers. For accurate work, particularly in the case of small crystals, a type of instrument

Introduction

known as a reflection goniometer is used. This is an instrument upon which the crystal to be measured is mounted so as to reflect beams of light from its faces through a telescope to the eye. The size of the angle through which a crystal has to be turned in order to throw successive beams of light from two adjacent faces into the telescope determines the angle existing between the faces. A sim pler instrument used for approximate work and with larger crystals is known as a contact goniometer. Its character and use are illustrated by Fig. 4.

The regular internal structure of crystals requires that the ultimate individual mineral units must be at least physically alike. A physical likeness between these units necessitates that they should also be the same chemically, or at least closely similar. Conse quently we can state that in general a crystal must be made up of a regular assemblage of units which are chemically the same, and therefore that a crys tallized mineral must have a definite and uniform chemical composition. This statement is a general one and will suffice for the present; certain modifications will be found stated on page 84 under isomorphism. A crystal is a guaranty of the chemical homogeneity of a mineral. From this it follows that only definite chemical com pounds are capable of crystallization.

To sum up the conclusions of the preceding paragraphs: A crystal is a solid with definite chemical composition, which possesses a definite internal arrangement of its mineral units. These internal

Fig. 4. Contact Goniometer.

characteristics are expressed outwardly in a definite external form. I And since the internal structure of the same substance is always comsinnt, the angles between the similar bounding planes of the crystals ofthat substance are also constant.

Manual Of Mineralogy

Ii. Symmetry

Crystals are grouped together into different classes according to the symmetry which they show. The symmetry of crystals is of three kinds, namely: 1. Symmetry in respect to a plane; 2. Symmetry in respect to a line; 3. Symmetry in respect to a point.

Symmetry, Plane. A symmetry plane is an imaginary plane which divides a crystal into halves, each of which is the mirror image of the other. Figure 5 will illustrate the character of such a plane. The shaded portion of the figure shows the position of the one plane of symmetry that a crystal of this sort possesses. For each face, edge or point on one side of the plane there is a corre sponding face, edge or point in a similar position on the other side of the plane.

Symmetry Axis . A symmetry axis is an imaginary line through a crystal about which the crystal may be revolved as upon an axis and repeat itself in appearance two or more times during the_ rev olution. In Fig. 6 the line C-C' is an axis of symmetry, for when the crystal represented is revolved upon it, it will have, after a revolution of 180°, the same appearance as at first; or in other words, similar planes, edges, etc., will appear in the places of the corresponding planes and edges of the original position. Point A' will occupy the original position of A, B' that of B, etc. Since the crystal is repeated twice in appearance during a complete revolu tion, this axis is said to be one of binary or twofold symmetry. In addition to axes of binary symmetry, we have axes of trigonal (threefold) , tetragonal (fourfold) and hexagonal (sixfold) symmetry.

Center of Symmetry. A crystal has a center of symmetry if an imaginary line is passed from some point on its surface through its center, and a similar point is found on the line at an equal dis tance beyond the center. The crystal represented in Fig. 7 has a center of symmetry, for the point A is repeated at A' on a line passing from A through the center, C, of the crystal, the distances AC and A'C being equal.

Symmetry Classes of Crystals. With the basic assumption

that crystal forms were the outward expression of an internal regu lar structure, crystallographers early attempted to develop theoreti-

Symmetry

cal structures that could account for the various kinds of symme try shown by crystals. In this way fourteen different fundamental parallelopipeds were derived which could act as unit cells in the building up of the crystal structure. While these fourteen different units could account for the more important of the symmetry classes of crystals they failed in certain cases. To explain these it was necessary to assume that the unit cells were grouped in respect to each other in some other way than the usual rectilinear arrange ment. By the assumption that the cells had been rotated or

A'

Fig. 7.

Symmetry Center.

Fig. 6.

Symmetry Axis.

Fig. 5.

Symmetry Plane.

moved in respect to each other it was possible to derive some sixtyfive different point systems from the original fourteen unit cells. Even then there were still some symmetry classes that remained unexplained. These have been accounted for by the further as sumption that the various point systems might interpenetrate each other. In this way a total of two hundred and thirty different arrangements of the unit cells was possible. AlLthese, however, fall into thirty-two distinct symmetry classes and from theoretical considerations it has been shown that these comprise all the pos sible symmetry classes of crystals. These thirty-two classes may be further grouped into six systems, the classes of each system hav ing certain close relations to each other. These systems are known as the Isometric, Tetragonal, Hexagonal,. Orthorhombic, Mono-

Manual Of Mineralogy

clinic and Triclinic Systems. All crystals will be found to belong to one or the other of these systems. As stated above, there are thirty-two possible subdivisions of these six systems, but the majority of them are only of theoretical interest, since practically all known species can be placed in one or the other of some ten or twelve classes.

Iii. Crystal Notation

A system of notation has been developed by which we can describe the different crystal classes and the crystal forms found in each. One of the important conceptions to this end is that of crystallographic axes.

Crystallographic Axes. Crystallographic axes are imaginary lines or directions within a crystal to which the crystal faces are referred and in terms of which they are described. In the differ ent systems the axes vary in number (three or four) , in their relative lengths and in the angles of inclination to each other. As a general case we will consider the crystallographic axes of the Orthorhombic System. They are three in number, at right angles to each other, and each has a characteristic relative length. Figure 8 represents such axes for the orthorhombic mineral sulphur. When placed in the proper position for description, or "orientated" as it is termed, one axis called a is horizontal and perpendicular to the observer, another axis, called b, is horizontal and parallel to the observer, while the third axis, called c, is vertical. The ends of each axis are designated by either a plus or a minus sign, the front end of o, the right-hand end of b and the upper end of c being positive, while in each case the opposite end is negative. When, as in the Ortho rhombic System, the three axes have different relative lengths, these values have to be determined experimentally by making the neces sary measurements on crystals of each mineral. Figure 9 would represent a crystal of sulphur in which each face of the crystal form, known as a pyramid, intercepts each axis at what is consid ered as its unit length. From the values obtained by measuring the angles between the different faces of this crystal an expression of the relative lengths of the three axes can be obtained by calcula-

Crystal Notation

tion. The length of the 6 axis is taken as unity and the lengths of the a and c axes are expressed in terms of it. The axial ratio for sulphur is a:b:c 0.813 : 1.00 : 1.903. It must be borne in mind that these lengths are only relative in their value. They do not represent any actual distances. A sulphur crystal may be of microscopic size or several inches in diameter, but in either case the abovi ' ' --u j.

-b

Fig. 10. Orthorhombic Prism.

Fig. 9.

Orthorhombic

Pyramid.

Fig. 8.

Orthorhombic Crystal Axes.

Parameters. Crystal faces are described according to their relations to the crystallographic axes. A series of numbers which indicate the relative distances by which a face intersects the different axes are called its parameters. A face which cuts all three axes at distances from the point of their intersection which are relatively the same as the unit lengths of the axes is said to have the following parameters: la, 16, lc (see Fig. 9). A face which cuts the two horizontal axes at distances which are relatively to each other as the unit lengths of those axes but is parallel to the vertical axis would have for parameters la, 16, ooc (see Fig. 10). If a face cuts the two horizontal axes at distances proportional to their unit lengths and cuts the vertical axis at a distance twice its relative unit length, it will have for parameters la, 16, 2c. It is to

Manual Of Mineralogy

be emphasized that these parameters are strictly relative in their values and do not indicate any actual cutting lengths. To further illustrate this, consider Fig. 11, which represents a possible sulphur crystal. The forms present upon it are two pyramids of different slope but each intersecting all three of the crystal axes when prop erly extended. The lower pyramid intersects the two horizontal axes at distances which are proportional to their unit lengths and if it was extended as shown by the dotted lines would also cut the vertical axis at a distance proportional to its unit length. The

parameters of the face of this form which cuts the positive ends of the three axes would be la, 16, lc. The upper pyramid would cut the two horizontal axes, as shown by the dotted lines, also at distances which, although greater than in the case of the lower pyramid, are still propor tional to their unit lengths. It cuts the vertical axis, however, at a dis tance which, when considered in re spect to its intersections with the horizontal axes, is proportional to onehalf of the unit length of c. The parameters of a face of this form would therefore be la, 16, \c. From

Fig. 11.

this example it will be seen that the parameters la, 16, do not in the two cases represent the same actual cutting distances but express only relative values. The parameters of a face do not in any way determine its size, for a face may be moved parallel to itself for any distance without changing the relative values of its intersections with the crystallographic axes.

Law of Definite Mathematical Ratio. It is to be noted that in general the ratio of the intercepts of a crystal face upon the crystallographic axes can be expressed by whole numbers or definite fractions. These numbers, or fractions, are commonly simple, such as 1, 2, 3, §, 3, §, etc., and in the great majority of cases are 1 or 00 . This law, that the axial intercepts of all crystal faces

Definitions Of Various Terms

form a definite mathematical ratio, is an extremely important one. It is a necessary corollary to the theoretical considerations given on page 8 and following.

Indices. Various methods of notation have been devised to express the intercepts of any crystal face upon the crystal axes, and several different ones are in common use. The most universally employed is the system of indices of Miller. While not as simple for a beginner, perhaps, as some one of the systems in which the parameters of the crystal faces are used, it adapts itself so much more readily to crystallographic calculations and consequently has so wide a, use that it seems wise to introduce it here.

The indices of a face consist of a series of whole numbers which have been derived from its parameters by their inversion and, if necessary, the subsequent clearing of fractions. The indices of a face are always given, so that the three numbers refer to the a, b and c axes respectively, and therefore ordinarily the letters which indicate the different axes are omitted. The pyramid illustrated in Fig. 9, which has la, 16, lc for parameters, would have 111 for indices. The face, Fig. 10, which has la, 16, aoc for parameters, would have 110 for indices. The face, Fig. 11, which has la, 16, jC for parameters, would have 112 for indices. A face which has la, 16, 2c for parameters would have 221 for indices.

Common use is made of what is known as the symbol of a form. A symbol of any form consists of the indices of the face having the simplest relations to the axes. This is used when it is desired to refer to some particular crystal form, and the symbol then stands for the whole form and not simply for the single face whose indices it is.

Iv. Definitions Of Various Terms

Crystal Form. By the expression "crystal form" is meant the assemblage of all similar faces which are possible with a certain degree of symmetry. In Fig. 9 is represented a crystal form known as a pyramid. In the particular symmetry class to which it belongs the three crystal axes are axes of binary symmetry and the axial planes are planes of symmetry. Under these conditions, if we

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assume the presence of the face A we must have the other seven faces also in order to satisfy the demands of the symmetry. In this case the assemblage of the eight pyramidal faces constitutes the crystal form. A crystal form does not necessarily make a solid figure. Consider Fig. 12, which is of a crystal of the Monoclimc System. In this system the b axis is an axis of binary symmetry and the plane of the a and c axes is a symmetry plane. Under these conditions, if we assume the presence of the plane b, the sym metry demands only the parallel face b' . So these two faces, being all the possible similar planes with this particular symmetry,

constitute a crystal form. There are three crystal forms present on the crystal represented in Fig. 12.

Crystal Habit. By the crystal habit of any mineral is meant the common and characteristic form or combination of forms in which, that mineral crystallizes. Galena, for example, has a cubic, magnetite an octahedral and garnet a dodeca hedral habit. By this is meant that, although these minerals are found in crystals which show other forms, such occurrences are comparatively rare, and their "habit" is to crystallize as indicated.

Crystal Combinations. In the great majority of cases, a crystal will show a combination of two or more crystal forms rather than one single form. In fact, many crystal forms, since they do not make a solid figure by themselves, must occur in combination with other forms. The combination in which it occurs may quite change the appearance of a form, and its recognition will depend upon the position and relation of its faces rather than upon their shape. Figure 13 is of a simple form known as a cube, and Fig. 14 is of a simple form known as an octahedron. Figure 15 shows a com bination of the two, in which the corners of the cube are truncated by the faces of the octahedron, while Fig. 16 shorn the same two forms in a combination in which the points of the octahedron are

Definitions Of Various Terms

truncated by the faces of the cube. When a corner or an edge of one form is replaced by a face of another form, the first is said to be truncated by the second. If an edge is replaced by two similar faces it is said to be beveled.

Fig- 13. Fig. 14. Fig. 15. Fig. 16.

Cube. Octahedron. Cube Truncated Octahedron Trun-

by Octahedron. cated by Cube.

Crystal Distortion. It seldom happens that the conditions for crystal growth are such as to permit the development of crystals of ideal symmetry. The crystal may have grown more rapidly in one direction than in another; other surrounding minerals may have interfered, and in various ways its symmetrical growth been prevented. Such a crystal is said to show distortion. Ordinarily

the amount of distortion is not so great as to prevent one from readily imagining what the ideally developed crystal would be like and so determining its symmetry and character. It is to be noted that the real symmetry of a crystal does not depend upon the sym metrical shape and size of its faces, but rather upon the symmetrical arrangement of its interfacial angles. In the Figs. 17 and 18, 19 and 20, 21 and 22, are given various crystal forms, first ideally developed and then distorted.

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Crystal Pseudomorphs. At times we find a mineral occur ring in crystals which prove to be not the characteristic forms for that mineral, but are rather the typical forms of some other species. Such crystals are said to be nseiulmiornhs nr forms They originate in various ways. The mineral mav have changed in its composition without, however, changing its crystal form. We find, for example, that cuprite, Cu20, frequently alters to malar chite, but without a change in the crystal shape. The resulting crystals would have the composition of malachite but the crystal form of cuprite. Another mode of origin is to have one mineral deposited on the crystals of another and so ng if.

wore, a eg fit nf *hp Smithsonite, ZnC03, is at times found in pseudomorphic crystals whose forms are those of calcite. In this case the smithsonite has been deposited in a thin layer over the crystal of calcite, which may have subsequently been removed. The resulting crystal is a pseudomorph of smithsonite after calcite. Pseudomorphs cannot be regarded as true crystals, since their

internal structure not, to the outward crystal

y'fsstu

( Twin Crystals. When two or more crystals intergrow accord- l ing to some definite law, the resulting group is said to be a twin ) crystal. The different members, ordinarily two, of a twin crystal / have usually a plane, known as a twinning plane, or an axis, known as a twinning axis, which is common to both. In Fig. 23, which represents a twin crystal of fluorite, we have two cubes intergrown in such a way that the diagonal axis A- A' is common to the two individuals. The individual, the faces of which are shaded in

Isometric System

the figure, lies as if it had been turned about this axis from the posi tion occupied by the other individual through an angle of 60 degrees. The line A-A' is known as the twinning axis. In Fig. 24 is represented a twinned octahedron. The two individuals here are grown together with an octahedral face in common. It will be noted that the composition plane, which is shaded, is parallel to one face of each individual. This plane is known as the twinning

Fig. 23. Twinned Cubes.

Fig. 24. Twinned Octahedron.

plane. The twin of Fig. 23 is known as a penetration twin, since the two individuals interpenetrate each other; while the twin of Fig. 24 is a contact twin, since the two individuals lie simply in contact with each other upon a certain plane.

V. Isometric System

Crystallographic Axes. The crystallographic axes of the Iso metric System are three in number, of equal lengths, and make right angles with each other. When properly orientated one axis is vertical and the other two are horizontal, one being parallel and the other perpen dicular to the observer, as is shown in Fig. 25. Since the three axes are identical in character, they are inter changeable, and any one of them may serve as the vertical axis, etc. In giv ing the indices of a face of an iso metric form, the order of the axes,

etc., is the same as described in a previous paragraph, page 15.

1 Fig. 25. Isometric Axes.

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Normal Class

Symmetry and Forms. The symmetry shown by the crystals of the Normal Class of the Isometric System is as follows. The three crystallographic axes are axes of tetragonal symmetry (see Fig. 26). There are also four diagonal axes of trigonal symmetry. These axes emerge in the middle of each of the octants formed by

Fig. 29.

Fig. 30.

Planes of Symmetry, Isometric System, Normal Class.

the intersection of the crystallographic axes (see Fig. 27). Further, there are six diagonal axes of binary symmetry, each of which bisects one of the angles between two of the crystallographic axes, as illustrated in Fig. 28.

This class shows nine planes of symmetry, three of them being known as the axial planes, since each includes two crystallographic axes (see Fig. 29), and six being called diagonal planes, since each bisects the angle between two of the axial planes (see Fig. 30).

Isometric System

To summarize the symmetry of this class:

3 crystallographic axes of tetragonal symmetry;

4 diagonal axes of trigonal symmetry;

6 diagonal axes of binary symmetry;

3 axial planes of symmetry;

6 diagonal planes of symmetry.

This symmetry, which is of the highest degree possible in solids with plane surfaces, defines the Normal Class of the Isometric System. Every crystal form and every combination of forms that belongs to this class must show its complete symmetry. It is important to remember that in this class the three crystallographic axes are axes of tetragonal symmetry, since this fact distinguishes the class from all others and by means of it the crystallographic axes can be easily located and a crystal properly orientated.

The forms of the Isometric System, Normal Class, are as follows:

1. Cvhe or Hexahedron. The cube is a form composed of six square faces which make 90° angles with each other. Each face intersects one of the crystallographic axes and is parallel to the other two. Its symbol is (100). Fig. 31 represents a simple cube.

a ,ooi

j

100 !„.-

a

i

i

2. Octahedron. The octahedron is a form composed of eight equilateral triangular faces, each of which intersects all three of the crystallographic axes equally. Its symbol is (111). Fig. 32 represents a simple octahedron and Figs. 33 and 34 show combina tions of a cube and an octahedron. When in combination the

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octahedron is to be recognized by its eight similar faces, each of which is equally inclined to the three crystallographic axes. It is to be noted that the faces of an octahedron truncate symmetrically the corners of a cube.

3. Dodecahedron. The dodecahedron is a form composed of twelve rhombic-shaped faces. Each face intersects two of the crystallographic axes equally and is parallel to the third. Its symbol is (110). Fig. 35 shows a simple dodecahedron, Fig. 36 shows a combination of dodecahedron and cube, Figs. 37 and 38

Fig. 36.

Cube and Dodecahedron.

Fig. 37.

Octahedron and Dodecahedron.

combinations of dodecahedron and octahedron, and Fig. 39 a combination of cube, octahedron and dodecahedron. It is to be noted that the faces of a dodecahedron truncate the edges of both the cube and the octahedron.

Isometric System

4. Tetrahexaheclron. The tetrahexahedron is a form composed of twenty-four isosceles triangular faces, each of which intersects one axis at unity, the second at some multiple, and is parallel to the third. There are a number of tetrahexahedrons which differ from each other in respect to the inclination of their faces. Perhaps

Dodecahedron and Octahedron.

Cube, Octahedron and Dodecahedron.

a

e

a

&

t

Fig. 41.

Cube and Tetrahexahedron.

the one most common in occurrence has the parameter relations la, 2b, oo c, the symbol of which would be (210). The symbols of other forms are (310), (410), (320), etc. It is helpful to note that the tetrahexahedron, as its name indicates, is like a cube, the faces of which have been replaced by four others. Fig. 40 shows a simple tetrahexahedron and Fig. 41a cube with its edges beveled by the faces of a tetrahexahedron.

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5. Trapezohedron or Tetragonal Trisoctahedron. The trapezohedron is a form composed of twenty-four trapezium-shaped faces, each of which intersects one of the crystallographic axes at unity and the other two at equal multiples. There are various trapezohedrons with their faces having different angles of inclination. A common trapezohedron has for its parameters la, 26, 2c, the symbol

Dodecahedron and Trapezohedron.

Fig. 44.

Dodecahedron and Trapezohedron.

Fig. 45.

Cube and Trapezohedron.

for which would be (211). The symbols for other trapezohedrons are (311), (411), (322), etc. It will be noted that a trapezohedron is an octahedral-like form and may be conceived of as an octahe dron, each of the planes of which has been replaced by three faces. Consequently it is sometimes called a tetragonal trisoctahedron. The qualifying word, tetragonal, is used to indicate that each of its faces has four edges and to distinguish it from the other trisoctahe-

Isometric System

dral form, the description of which follows. Trapezohedron is the name, however, most commonly used. The following are aids to the recognition of the form when it occurs in combinations: the three similar faces to be found in each octant; the relations of each face to the axes; and the fact that the middle edges between the three faces in any one octant go toward points which are equi distant from the ends of the two adjacent crystallographic axes. Fig. 42 shows a simple trapezohedron, and Figs. 43 and 44 show each a trapezohedron in combination with a dodecahedron. It is to be noted that the faces of the common trapezohedron (211) (Fig. 43) truncate the edges of the dodecahedron. Fig. 45 shows a combination of cube and trapezohedron.

6. Trisoctahedron or Trigonal Trisodahedron. The trisoctahedron is a form composed of twenty-four isosceles triangular faces, each of which intersects two of the crystallographic axes at unity

Fig. 47.

Octahedron and Trisoctahedron.

and the third axis at some multiple. There are various trisoctahedrons the faces of which have different inclinations. A common trisoctahedron has for its parameters la, lb, 2c, its symbol being (221). Other trisoctahedrons have the symbols (331), (441), (332), etc. It is to be noted that the trisoctahedron, like the trapezohe dron, is a form that may be conceived of as an octahedron, each face of which has been replaced by three others. Frequently it is spoken of as the trigonal trisoctahedron, the modifying word indi cating that its faces have each three edges and so differ from those of the trapezohedron. But when the word "trisoctahedron is

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used alone it refers to this form. The following points would aid in its identification when it is found occurring in combinations: the three similar faces in each octant; their relations to the axes; and the fact that the middle edges between them go toward the ends of the crystallographic axes. Fig. 46 shows the simple trisoctahedron and Fig. 47 a combination of a trisoctahedron and an octahedron. It will be noted that the faces of the trisoctahedron bevel the edges of the octahedron

7. H exoctahedron. The hexoctahedron is a form composed of forty-eight triangular faces, each of which cuts differently on all

Fig. 48.

Hexoctahedron.

Cube and Hexoctahedron.

Dodecahedron and Hexoctahedron.

Dodecahedron, Trapezohedron and Hexoctahedron.

three crystallographic axes. There are several hexoctahedrons, which have varying ratios of intersection with the axes. A com mon hexoctahedron has for its parameter relations la, §6, 3c, its symbol being (321). Other hexoctahedrons have the symbols

Isometric System

(421), (531), (432), etc. It is to be noted that the hexoctahedron is a form that may be considered as an octahedron, each face of which has been replaced by six others. It is to be recognized when in combination by the facts that there are six similar faces hi each octant and that each face intercepts the three axes differently. Fig. 48 shows a simple hexoctahedron, Fig. 49 a combination of cube and hexoctahedron, Fig. 50 a combination of dodecahedron and hexoctahedron, and Fig. 51 a combination of dodecahedron, trapezohedron and hexoctahedron.

Zonal Relations of Isometric Forms. A crystal . consists of a series of faces, all nf which lie parallel to some one crystal di rection and whose intersections with each other are all parallel to tins direction. For instance in Fig. 36, p. 22, the cube and dodec ahedron planes, marked a and d, fall into three zones, each zone being parallel to one of the crystal axes; similarly in Fig. 34 the cube and octahedron faces fall into six similar zones with the edges between the faces lying parallel in each case to one of the diagonal axes of binary symmetry.

Figs. 50 and 51, p. 26 also show clearly zones between the faces d, s, and n. By learning the zonal relations of the isometric forms it be comes simple to determine the character of an unknown face. Fig. 52 will help in this respect. It gives in the form of a diagram the positions in relation to each other of all the possible forms in the Normal Class. It will be noticed that any face falling in the zone between cube and dodecahedron (or in other words truncating the edge between them) must belong to a tetrahexahedron; similarly any face between cube and octahedron belongs to a trapezohedron; between dodecahedron and octahedron will fall the trisoctahedron; while lastly a face that does not occur in any one of these zones must belong to a hexoctahedron.

Octahedron

Fig. 52.

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Therefore, to determine the forms present on any isometric crystal, it is only necessary to discover the axial directions (axes of tetragonal symmetry); orientate the crystal; recognize the cube, octahedron, and dodecahedron faces that may be present, or, if they fail, to realize where they would properly occur, and then by applying the principle of zonal relations determine the character of the other forms upon the crystal.

Occurrence of Isometric Forms. The cube, octahedron and dodecahedron are the most common of the isometric forms. The trapezohedron is also frequently observed on a few minerals. The other forms, the tetrahexahedron, trisoctahedron and hexoctahedron, are rare and are ordinarily to be observed only as small truncations in combinations.

The following is a list of the commoner minerals upon the crystals of which each form is prominent :

Cube: Galena, halite, sylvite, fluorite, cuprite.

Octahedron: Spinel, magnetite, franklinite, chromite.

Dodecahedron: Magnetite, garnet.

Trapezohedron: Leucite, garnet, analcite.

Pyritohedral Class

The Pyritohedral Class is one of the subordinate divisions of the Isometric System. It differs from the Normal Class, since its crystals commonly show forms that do not possess as high a sym metry as those of that class. The name of the class is derived from that of its chief member, pyrite.

Symmetry and Forms. The symmetry of the Pyritohedral Class is as follows: The three crystal axes are axes of binary sym metry; the four diagonal axes, each of which emerges in the middle of an octant, are axes of trigonal symmetry; the three axial planes are planes of symmetry (see Figs. 53 and 54).

The characteristic forms of the Pyritohedral Class are as follows:

1. PyrifaludwiL or Pentagonal Dodecahedron. This form con sists of twelve pentagonal-shaped faces, each of which intersects one crystallographic axis at unity, the second axis at some multiple, and is parallel to the third. There are a number of pyritohedrons

Isometric System

which differ from each other in respect to the inclination of their faces. Perhaps the most common in occurrence has the parameter relations la, 2b, ooc, the symbol of which would be (210) (see Fig. 55). It is to be noted that the parameter relations of the pyritohedron are the same as those of the tetrahexahedron (see page 23). A pyritohedron may be considered as derived from a corresponding tetrahexahedron by the omission of alternate faces

Symmetry of Pyritohedral Class, Isometric System.

Fig. 56.

Showing Relation between Pyrito hedron and Tetrahexahedron.

and the extension of those remaining. Fig. 56 shows the relations of the two forms, the shaded faces of the tetrahexahedron being those which when extended wrould form the faces of the pyrito hedron.

2. Diploid. The diploid is a rare form. It is composed of twenty-four faces which correspond to one-half the faces of a hexoctahedron. Fig. 57 represents a diploid.

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In addition to the two forms described above, minerals of this class show also the cube, octahedron, dodecahedron, trapezohedron and trisoctahedron. Sometimes these forms may appear alone and so perfectly developed that they cannot be told from the forms of the Normal Class. This is often true of octahedrons of pyrite. Usually, however, they will show by the presence of striation lines or etching figures that they do not possess the high symmetry of the Normal Class but conform rather to the symmetry of the

Fig. 58. Striated Cube.

a

Fig. 59. Cube and Pyritohedron.

Fig. 60. Octahedron and Pyritohedron.

Pyritohedral Class. This is shown in Fig. 58, which represents a cube of pyrite with characteristic striations, which are so disposed that the crystal shows the lower symmetry. Fig. 59 represents a combination of cube and pyritohedron, in which it will be noted that the faces of the pyritohedron truncate unsymmetrically the edges of the cube. Figs. 60, 61 and 62 represent combinations of pyritohedron and octahedron with various developments. Fig. 63 shows a cube truncated with pyritohedron and octahedron. Fig. 64 represents a combination of cube and the diploid / (421).

Isometric System

These figures should be studied in order to impress upon one's mind the characteristic symmetry of the class.

The chief mineral of the Pyritohedral Class is pyrite; other much rarer members are smaltite, chloanthite, cobaltite, gersdorffite and sperrylite.

Octahedron and Pyritohedron. Pyritohedron and Octahedron.

Fig. 63. Fig. 64.

Pyritohedron, Cube and Octahedron. Diploid and Cube.

Tetrahedral Class

Another subordinate division of the Isometric System is known as the Tetrahedral Class, deriving its name from its chief form, the tetrahedron.

Symmetry and Forms. The symmetry of this class is as follows: The three crystallographic axes are axes of binary sym metry ; the four diagonal axes are axes of trigonal symmetry; there are six diagonal planes of symmetry- (see Figs. 65 and 66).

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The characteristic forms of the Tetrahedral Class are as follows: 1. Tetrahedron. The tetrahedron is a form composed of four equilateral triangular faces, each of which intersects all of the crystallographic axes at equal lengths. It can be considered as

Fig. 66.

Symmetry of Tetrahedral Class, Isometric System.

derived from the octahedron of the Normal Class by the omission of the alternate faces and the extension of the others, as shown in Fig. 67. This form, shown also in Fig. 68, is known as the positive

tetrahedron and has for its sym bol (111). If the other four faces of the octahedron had been ex tended, the tetrahedron resulting would have had a different orienta tion, as shown in Fig. 69. This is known as the negative tetrahedron and has for its symbol (111). The positive and negative tetrahedrons when occurring alone are geomet rically identical, and the only reason for recognizing the possi bility of the existence of two dif ferent orientations lies in the fact that at times they may occur truncating each other, as shown in Fig. 70. If a positive and negative tetrahedron occurred together with equal development, the resulting crystal could not be distinguished from an octar

Showing Relation between Octa hedron and Tetrahedron.

Isometric System

hedron, unless, as is usually the case, the faces of the two forms showed different lusters, etchings or striations that would serve to differentiate them.

Positive Tetrahedron. Negative Tetrahedron.

Positive and Negative Tetrahedrons.

Fig. 71.

Tristetrahedron.

Deltoid Dodecahedron.

Fig. 73.

Hexakistetrahedron.

Cube and Tetrahedron.

Tetrahedron and Cube.

Other possible but rare tetrahedral forms are the following: The tristetrahedron (Fig. 71), the faces of which correspond to onehalf the faces of a trapezohedron; the deltoid dodecahedron (Fig.

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72), the faces of which correspond to one-half those of the trisoctahedron; the hexakistetrahedron (Fig. 73), the faces of which cor respond to one-half the faces of the hexoctahedron.

Tetrahedron and Dodecahedron. Dodecahedron, Cube and Tetrahedron.

The cube and dodecahedron are also found on minerals of the Tetrahedral Class. Figs. 74 and 75 show combinations of cube and tetrahedron. It will be noted that the tetrahedron faces truncate the alternate corners of the cube, or that the cube faces

truncate the edges of a tetrahedron. Fig. 76 shows the combination of tetrahedron and dodecahedron. Fig.

77 represents a combination of cube, dodecahedron and tetrahedron. Fig.

78 shows a combination of tetrahedron and tristetrahedron.

Tetrahedrite and the related tennantite are the only common min erals that ordinarily show distinct tetrahedral forms. Sphalerite occa sionally exhibits them, but commonly its crystals are quite com plex and distorted.

Fig. 78. Tetrahedron and Tristetrahedron .

Characteristics of Isometric Crystals

The striking characteristics of isometric crystals which would aid in their recognition may be summarized as follows:

The crystals are equidimensional iru three directions at right angles to each other. These three directions in crystals of the

Tetragonal System

Normal Class are axes of tetragonal symmetry. The crystals commonly show faces that are squares or equilateral triangles or these figures with truncated comers. They are characterized by the large number of similar faces, the smallest number on any form of the Normal Class being six. Every form by itself would make a solid.

Important Isometric Angles. Below are given various inter-, facial angles which may assist in the recognition of the commoner isometric forms :

Cube (100) A cube (010) 90° 0' 0".

Octahedron (111) A octahedron (Ill) 70° 31' 44".

Dodecahedron (110) A dodecahedron (101) 60° 0' 0".

Cube (100) A octahedron (111) 54° 44' 8".

Cube (100) A dodecahedron (110) 45° 0' 0".

Octahedron (111) A dodecahedron (110) 35° 15' 52".

Vi. Tetragonal System

Crystallographic Axes. The crystallographic axes of the Tetragonal System are three in number and make right angles with each other. The two horizontal axes are equal in length and inter changeable, but the vertical axis is of some different length which varies with each tetragonal mineral.

Fig. 79 represents the crystallo graphic axes for the tetragonal mineral zircon. The length of the horizontal axes is taken as unity, and the relative length of the ver tical axis is expressed in terms of the horizontal. This length has to be determined for each tetragonal mineral by measuring the interfacial angles on a crystal and making the proper calculations. For zircon the length of the vertical axis is expressed as c 0.640. The proper orientation of the crystallographic axes and the method of their notation is like that of the Isometric System and is shown in Fig. 79.

Fig. 79. Tetragonal Axes.

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Normal Class

Symmetry and Forms. The symmetry of the Normal Class of the Tetragonal System is as follows : The vertical crystallographic axis is an axis of tetragonal symmetry. There are four horizontal axes of binary symmetry, two of which are coincident with the crystallographic axes, while the other two bisect the angles be tween these. Fig. 80 shows the axes of symmetry. There are four vertical and one horizontal planes of symmetry. Each verti cal plane of symmetry passes through one of the horizontal axes of

symmetry. The position of the planes of symmetry is shown in Fig. 81.

Fig. 81.

Fig. 80.

Symmetry of Normal Class, Tetragonal System.

The forms of the Normal Class, Tetragonal System, are as fol lows:

1. Prism of First Order. The prism of the first order consists of four rectangular vertical faces, each of which intersects the two horizontal crystallographic axes equally. Its symbol is (110). The form is represented in Fig. 82.

2. Prism of Second Order. The prism of the second order con sists of four rectangular vertical faces, each of which intersects one horizontal crystallographic axis and is parallel to the other two axes. Its symbol is (100). The form is represented in Fig. 83. The prisms of the first and second order are identical forms, except for their orientation. They can be converted into each other by a revolution about the vertical axis of 45°. Since both may occur together upon the same crystal it is necessary to recognize the two forms.

Tetragonal System

3. Ditetragonal Prism. The ditetragonal prism is a form con sisting of eight rectangular vertical faces, each of which intersects the two horizontal crystallographic axes unequally. There are various ditetragonal prisms, depending upon their differing rela tions to the horizontal axes. The symbol of a common form is (210), which is represented in Fig. 84.

Fig. 82.

Fig. 83.

Fig. 84.

First Order Prism.

Second Order Prism. Ditetragonal Prism.

4. Pyramid of First Order. The pyramid of the first order is a form consisting of eight isosceles triangular faces, each of which intersects all three crystallographic axes, the intercepts upon the two horizontal axes being equal. There are various pyramids of the first order, depending upon the inclination of their faces. The unit pyramid which intersects all the axes at their unit lengths is the most common, its symbol being (111). Symbols for other pyramids of the first order are (221), (331), (112), (113), etc. Fig. 85 represents the unit pyramid on zircon.

5. Pyramid of Second Order. The pyramid of the second order is a form composed of eight isosceles triangular faces, each of which intersects one horizontal axis and the vertical axis and is parallel to the second horizontal axis. There are various pyramids of the second order, with different intersections upon the vertical axis. The most common form is the unit pyramid, which has (101) for its symbol. Other pyramids of the second order would have the symbols (201), (301), (102), (103), etc. Fig. 86 represents a unit pyramid of the second order upon zircon. The same relationship

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exists between the pyramids of the first and second order as in the case of the corresponding prisms; see above.

6. Ditetragonal Pyramid. The ditetragonal pyramid is a form composed of sixteen isosceles triangular faces, each of which inter-

Fig. 85.

First Order Pyramid.

Fig. 86.

Second Order Pyramid.

Fig. 87.

Ditetragonal Pyramid.

sects all three of the crystallographic axes, cutting the two hori zontal axes at different lengths. There are various ditetragonal pyramids, depending upon the different axial intersections possible. One of the most common is the pyramid having (311) for its sym bol. This is shown as it would appear upon zircon in Fig. 87.

Fig. 88. Zircon. Fig. 89. Zircon.

Fig. 90. Zircon.

7. Basal Pinacoid. The basal pinacoid, basal plane, or base, as it is variously called, is a form composed of two horizontal faces. Its symbol is (001). It is shown hi combination with a prism in Figs. 82, 83 and S4.

Tetragonal System

Tetragonal Combinations. The different pyramids are the only tetragonal forms that can occur alone, and even they are ordinarily found in combination with other forms. Characteristic combina tions are represented in Figs. 88-97.

Fig. 92. Vesuvianite. Fig. 93. Vesuvianite.

Fig. 95. Cassiterite.

Sphenoidal Class

The Sphenoidal Class corresponds in the Tetragonal System to the Tetrahedral Class in the Isometric System. It is characterized by the following symmetry: The three crystallographic axes are axes of binary symmetry (see Fig. 98), and there are two vertical diagonal planes of symmetry (see Fig. 99).

Sphenoid. The characteristic form of the class is known as a sphenoid (from a Greek word meaning alike). It consists of four isosceles triangular faces which intersect all three of the crystallo graphic axes, the intercepts on the two horizontal axes being equal.

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The faces correspond in their position to the alternating faces of the tetragonal pyramid of the first order. There may be different sphenoids, depending upon their varying intersections with the vertical axes. Two different sphenoids are shown in Figs. 100 and 101. There may also be a positive and a negative sphenoid, the combination of the two being represented in Fig. 102.

Fig. 98.

Fig. 99.

Symmetry of Sphenoidal Class, Tetragonal System.

Fig. 100. Sphenoid.

The sphenoid differs from the tetrahedron in the fact that its vertical crystallographic axis is not of the same length as the hori zontal axes. The only common sphenoidal mineral is chalcopyrite. The length of the vertical axis in chalcopyrite is veiy close to that of the horizontal axes, c 0.985. In the case of the unit sphenoid, therefore, it would require accurate measurements in order to differentiate it from an isometric tetrahedron. Chalcopyrite crystals ordinarily show only the unit sphenoid (Fig. 101), but at times show a steeper sphenoid (Fig. 100).

Hexagonal System

Tri-Pyramidal Class

Another division of lower symmetry of the Tetragonal System is known as the Tri-pyramidal Class. It is characterized by a form known as the pyramid of the third order. This form consists of eight faces which correspond in their position to one-half of the faces of a ditetragonal pyramid. The minerals found in this class are few and rare. Moreover, their crystals seldom show the faces of the pyramid of the third order, and when these do occur they are usually quite small. Therefore it seems hardly necessary in this place to consider this class in greater detail.

Fig. 103 is of a crystal of scapolite, upon which the faces of the third-order pyramid z are shown.

Characteristics of Tetragonal Crystals

Since the only common tetragonal mineral that does not belong to the Normal Class is chalcopyrite, which, moreover, is to be easily recognized by its general physical characteristics, we may confine ourselves here to the consideration only of the crystals of the Normal Class.

The striking characteristics of tetragonal crystals may be sum marized as follows: One axis of tetragonal symmetry; the length of the crystal parallel to this axis is usually greater or less than its other dimensions; the cross section of a crystal when viewed in the direction of the axis of tetragonal symmetry consists usually of a square or a truncated square.

Vii. Hexagonal System

Crystallographic Axes. The crystallographic axes of the hexagonal system are four in number. Three of these lie in the horizontal plane, while the fourth is vertical. The three horizontal axes are of equal length and interchangeable. They make angles of 60° and 120° with each other. The vertical axis varies in its relative length for each hexagonal mineral, and this is expressed in

Fig. 103. Scapolite.

Manual Of Mineralogy

terms of the length of the horizontal axes, which is taken as unity. Thus in the case of beryl, the vertical axis, designated as c, has a length which in relation to the length of the horizontal axes can be expressed as c 0.499.

When properly orientated, one of the horizontal crystallographic axes is parallel to the observer, and the other two make 30° angles on either side of a line perpendicular to him. Fig. 104 shows the proper position of the horizontal axes when viewed in the direction

of the vertical axis. As the three horizontal axes are interchange able with each other, they are usually designated at, a2 and o3. Note that cm is to the left of the observer writh its positive end at the front, that a2 is parallel to the observer and its positive end is at the right, while a3 is to the right of the observer and its positive end is at the back. Fig. 105 shows the four axes in clinographic pro jection. In giving the indices of any face upon a hexagonal crystal four numbers must be given, since there are four axes. The num bers referring to the intercepts of the face with the three horizontal axes are given first in their proper order, while the number referring to the intercept on the vertical axis is given last.

Normal Class

Symmetry and Forms. The symmetry of the Normal Class of the Hexagonal System is as follows: The vertical crystallo graphic axis is an axis of hexagonal symmetry. There are six

Hexagonal System

horizontal axes of binary symmetry, three of them being coincident with the crystallographic axes and the other three lying midway between them (see Fig. 106). There is a horizontal plane of sym metry and six vertical planes of symmetry (see Fig. 107). The forms of the Normal Class are as follows:

Fig. 106. Fig. 107

Symmetry of Normal Class, Hexagonal System.

Prism of First Order.

Prism of Second Order.

Fig. 110.

Dihexagonal Prism.

1. Prism of First Order. This is a form consisting of six rectan gular vertical faces each of which intersects two of the horizontal crystallographic axes equally and is parallel to the third. Fig. 108 shows the prism of the first order. The symbol for the form is (1010).

2. Prism of Second Order. This is a form consisting of six rec tangular vertical faces, each of which intersects two of the horizontal

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axes equally and the intermediate horizontal axis at one-half this distance. Fig. 109 shows the prism of the second order. The symbol for the form is (1120). As in the Tetragonal System, the prisms of the first and second order are geometrically identical forms, the distinction between them lying only in their orientation.

3. Dihexagonal Prism. The dihexagonal prism has twelve rec tangular vertical faces, each of which intersects all three of the horizontal crystallographic axes at different lengths. There are various dihexagonal prisms, depending upon their differing rela tions to the horizontal axes. The symbol of a common dihexagonal prism is (2130) (see Fig. 110).

4. Pyramid of First Order. This form consists of twelve isosceles triangular faces, each of which intersects two of the horizontal

Fig. 111.

Fig. 112.

Fig. 113.

Pyramid of First Order. Pyramid of Second Order. Dihexagonal Pyramid.

crystallographic axes equally, is parallel to the third horizontal axis and intersects the vertical axis (see Fig. 111). There are various pyramids of the first order possible, depending upon the inclination of their faces. The unit-form would have the symbol (1011).

5. Pyramid of the Second Order. This is a form composed of twelve isosceles triangular faces, each of which intersects two of the horizontal axes equally, the third and intermediate horizontal axis at one-half this distance, and also intersects the vertical axis (see Fig. 1 1 2) . There are various pyramids of the second order possible, depending upon the inclination of their faces. A common form

Hexagonal System

would have for its symbol (1122). The relations between the pyramids of the first and second order is the same as between the corresponding prisms; see above.

6. Dihexagonal Pyramid. The dihexagonal pyramid is a form of twenty-four isosceles triangular faces, each of which intersects all three of the horizontal axes differently and intersects also the vertical axis. This form is shown in Fig. 1 13. There are different dihexagonal pyramids which vary in their intercepts, one of the most common having for its symbol (2131).

7. Basal Pinaeoid. The basal pinacoid is a form composed of two horizontal faces. It is shown in combination with the differ ent prisms in Figs. 108, 109 and 110. Its symbol is (0001).

Figs. 114-117 show various combinations of the forms of this class.

Fig. 114.

Beryl Crystals.

Tri-Pyramidal Class

A division of the Hexagonal System showing lower symmetry than that of the Normal Class is known as the Tri-pyramidal Class. It has a vertical axis of hexagonal symmet ry and a hori zontal plane of symmetry. It is characterized by the form known as the pyramid of the third order. This form consists of twelve faces, which corre spond in their position to one-half of the faces of a dihexagonal

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pyramid. The minerals of the Apatite Group are the only ones of importance in this class, and upon their crystals the pyramid of the third order is rarely to be seen. When it is observed it shows usually only small faces. Fig. 118 represents a complex crystal of apatite with the faces of a third-order pyramid (m) upon it.

Hemimorphic Class

The crystals of certain rare minerals show the forms of the Normal Class but with hemimorphic develop ment. A hemimorphic crystal is one that shows different forms or combinations of forms at the opposite ends of a symmetry axis. Fig. 119 represents a crystal of zincite with a prism terminated by a pyramid above and a basal pinacoid below.

Fig. 119. Zincite.

Rhombohedral Class. Normal Division

The forms of this class are to be referred to the hexagonal crystallographic axes, but show a lower symmetry than those of the Normal Class.

Symmetry and Forms. The vertical crystallographic axis is one of trigonal symmetry, and the three horizontal crystallo-

Fig. 120. Fig. 121.

Symmetry of Rhombohedral Class, Hexagonal System.

graphic axes are axes of binary symmetry (see Fig. 120). There are three vertical planes of symmetry7 bisecting the angles between the horizontal axes (see Fig. 121).

Hexagonal System

1. Rhombohedron. The rhombohedron is a form consisting of six Rhombic-shaped faces, which correspond in their position to the alternate faces of a hexagonal pyramid of the first order. The relation of these two forms to each other is shown in Fig. 122. There may be two different orientations of the rhombohedron. A positive rhom bohedron is shown in Fig. 123 and a negative rhombohedron in Fig. 124.

It is to be noted that when properly orientated the positive rhombohedron has one of its faces, and the negative rhombohedron one of its edges, to ward the observer. There are vari ous rhombohedrons, which differ from each other in the inclination of their faces. The symbol of the unit positive rhombohedron is (1011) and of the unit negative

Fig. 122. Showing Relation bebetween First Order Pyramid and Rhombohedron.

rhombohedron (Olll). Characteristic combinations of positive and negative rhombohedrons with each other and with other hexagonal forms are shown in Figs. 125-133. As in the case of

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the tetrahedron of the Isometric System, to which these forms are analogous, the distinction between the positive and negative rhombohedrons is only one of orientation.

Fig. 134. Showing Relation between Dihex- Fig. 135. Scalenohedron. agonal Pyramid and Scalenohedron.

Hexagonal System

2. Scalenohedron. This form consists of twelve scalene tri angular faces. These faces correspond in their position to the alternate pairs of faces of a dihexagonal pyramid. The relation of the two forms to each other is shown in Fig. 134. The striking characteristics of the scalenohedron are the zigzag middle edges which differentiate it from an ordinary pyramid and the alter nating, relatively obtuse and acute angles over the edges that meet at the vertices of the form. There are many different possible

Fig. 138. Calcite. Fig. 139. Caloite.

scalenohedrons, depending upon the varying slope of their faces. A common scalenohedron having the symbol (2131) is represented in Fig. 135. Characteristic combinations of scalenohedrons with other forms are shown in Figs. 136-139.

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Rhombohedral Class. Hemimorphic Division

Tourmaline crystals show the forms of the Rhombohedral Class but with hemimorphic development. They are also commonly characterized by the presence of three faces of a triangular prism. Figs. 140-143 represent characteristic hemimorphic tourmaline crystals.

Fig. 140. Tourmaline.

Fig. 142. Tourmaline.

Fig. 141. Tourmaline.

Rhombohedral Class. Tri-Rhombohedral Division

This is a subdivision of the Rhombohedral Class, which contains only a few and rare minerals. It is characterized by the forms known as the rhombohedrons of the second and third orders. The faces of a second-order rhombohedron correspond in position to one-half the faces of the second-order hexagonal pyramid, and those of the third order to one-quarter of the faces of the dihexagonal pyramid.

Orthorhombic System

Rhombohedral Class. Trapezohedral Division

The only important mineral of this class that is commonly found in crystals is quartz, and its crystals as a rule do not show forms other than those of the Rhombohedral Class, Normal Division. At times, however, small faces may occur of a form known as a trapezohedron, which shows a lower symmetry. This form has six faces, which correspond in their position to one-quarter of the faces of a dihexagonal pyramid. The quartz crystals are said to be right- or left-handed, depending upon whether these faces are to be observed truncating the edges between prism and rhombohedron faces at the right or at the left. Figs. 144 and 145 represent these two types.

Fig. 144.

Right-handed Quartz.

Fig. 145.

Left-handed Quartz.

Characteristics of Hexagonal Crystals

Hexagonal crystals are most readily recognized by the following facts: The vertical crystallographic axis is one of either hexagonal or trigonal symmetry. The crystals are commonly prismatic in habit. When viewed in the direction of the vertical axis, they usually show a hexagonal cross section.

Viii. Orthorhombic System

Crystallographic Axes. The crystallographic axes of the orthorhombic system are three in number. They make 90° angles with each other and are of unequal lengths. The relative lengths

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of the axes, or the axial ratio, has to be determined for each ortho rhombic mineral. Any one of the three axes may be chosen as the vertical or c axis. The longer of the other two is taken as the .b axis and is called the macro-axis. The shorter of the horizontal axes is taken as the a axis and is called the brachy-ams. The decision as to which of the three axes shall be chosen as the vertical or c axis depends usually upon the crystal habit of the mineral being considered. If its crystals commonly show an elongation in one direction, usually this direction is chosen as the c axis, see Figs. 157-

+c

-b

Pa +b

+a

Fig. 146.

Orthorhombic Axes.

Fig. 147.

Axes of Symmetry. Orthorhombic System.

Fig. 148.

Planes of Symmetry. Orthorhombic System.

159, p. 55. If on the other hand the crystals show a prominent pinacoid and therefore are tabular in habit, this pinacoid is usually taken as the horizontal (basal) pinacoid with the c axis normal to it, see Figs. 162-164, p. 55. Of course if a substance is well known and the orientation of its crystals given in the literature it is customary to conform to that orientation. The length of the axis which has been chosen as the b axis is taken as unity and the relative lengths of the a and c axes are given in terms of it. Fig. 146 represents the crystallographic axes for the orthorhombic mineral sulphur, whose axial ratio would be as follows: a:b :c 0.813 : 1 : 1.903.

Orthorhombic System

Normal Class

Symmetry and Forms. The symmetry of the Normal Class, Orthorhombic System, is as follows: The three crystallographic axes are axes of binary symmetry and the three axial planes are planes of symmetry (see Figs. 147 and 148).

1. Pyramid. An orthorhombic pyramid has eight triangular faces, each of which intersects all three of the crystallographic axes. There are various different pyramids with varying intercepts on the axes. A unit pyramid (see Fig. 149) would have for its symbol (111).

Fig. 149. Pyramid. Fig. 150. Prism and Base.

2. Prism. An orthorhombic prism has four vertical rectangular faces, each of which intersects the two horizontal axes. There are various prisms, depending upon their differing relations to the horizontal axes. A unit prism (see Fig. 150) would have for its symbol (110).

3. Macrodome. A macrodome is a form consisting of four rec tangular faces, each of which intersects the a and c axes and is parallel to the b or macro-axis. It is named from the axis to which it is parallel. There are various macrodomes with different axial intercepts. A unit form (see Fig. 151) would have for its symbol (101).

4. Brachydame. The brachydome consists of four rectangular faces, each of which intersects the b and c axes and is parallel to the a or brachy-axis. There are various brachydomes with different axial intercepts. A unit form (see Fig. 152) would have for its symbol (Oil).

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5. Mjacxofnnaeoid. The macropinacoid has two parallel faces, each of which intersects the a axis and is parallel to the b and c axes. It derives its name from the fact that it is parallel to the b or macro-axis. It is represented in Fig. 153 and its symbol is (100).

Fig. 151.

Macrodome and Braehypinacoid.

Brachydome and Macropinacoid.

6. Braehypinacoid. This is a form consisting of two parallel faces, each of which intersects the b axis and is parallel to the a (brachy) and the c axes. It is represented in Fig. 153 and its symbol is (010).

Fig. 153.

Macropinacoid, Braehypinacoid, and Basal Pinacoid.

7. Basal Pinacoid. The basal pinacoid is a form consisting of two horizontal faces. It is represented in Fig. 153 and its symbol is (001).

Combinations. Practically all orthorhombic crystals consist of combinations of two or more forms. Characteristic combinations of the various forms are given in Figs. 154-164.

Orthorhombic System

Fig. 154. Sulphur.

Fig. 157. Topaz.

Fig. 155. Sulphur.

Fig. 156. Staurolite.

Fig. 161. Anglesite.

Fig. 164. Celestite.

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Hemimorphic Class

The only orthorhombic mineral of importance belonging to this class is calamine. When its crystals are doubly terminated they show different forms at either end of the vertical axis. Fig. 165 represents a characteristic crystal.

Fig. 165. Calamine.

Characteristics of Orthorhombic Crystals

The most distinguishing characteristics of ortho rhombic crystals are as follows: The three chief directions at right angles to each other are of different lengths. These three directions are axes of binary symmetry. The crystals are commonly prismatic in their development and show usually cross sections that are either rectangles or truncated rectangles.

Ix. Monoclinic System

Crystallographic Axes. The crystallographic axes of the Monoclinic System are three in number. They are of unequal lengths. The axes a and b, and b and c, make 90° angles with each other, but a and c make some oblique angle with each other. The relative lengths of the axes and the angle between the a and c axes vary for each monoclinic mineral and have to be determined in each case from appropriate measurements. The a axis is known as the clino-axis, while the b axis is known as the ortho-axis. The length of the b axis is taken as unity and the lengths of the a and c axes are expressed in terms of it. When properly orientated the c axis is vertical, and b axis is horizontal and parallel to the observer, and the a axis is inclined downward toward him. The smaller of the two supplementary angles that a and c make with each other is designated as p. Fig. 166 represents the crystallographic axes of the monoclinic mineral orthoclase, the axial constants of which are expressed as follows: a :b :c 0.658; 1 : 0.555; /3 63° 57'.

In any monoclinic crystal the position of the b axis and that of the plane in which the a and c axes lie is fixed by the symmetry (see

Monoclinic System

Figs. 167 and 168). The directions which shall serve as the a and c axes, however, are matters of choice and will depend customarily upon the crystal habit. If the crystals of the substance show an elongated development (prismatic habit) parallel to some direction

Fig. 166. Monoclinic Axes.

in the a-c plane, that direction often serves as the c axis, see Figs. 175-177, p. 60. Further if there is a prominent sloping plane or planes, such as planes c in Figs. 180-182, or planes r in Figs. 177- 178, these may be taken as parallel to the inclined axis a. It is quite possible that there may be two, or even more, different

Fig. 167.

Fig. 168.

Symmetry of Monoclinic System.

choices as to the directions of the a and c axes in a monoclinic erystal that are equally good. Naturally once established, the orientation of the crystals of a given substance is followed in sub sequent descriptions.

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Normal Class

Symmetry and Forms. The symmetry of the Normal Class of the Monoclinic System is as follows: The crystallographic axis b is an axis of binary symmetry and the plane of the a and c axes is a plane of symmetry (see Figs. 167 and 168). The forms are as follows:

1. Pyramid. A monoclinic pyramid is a form consisting of four triangular faces, each of which intersects all three of the crystallo graphic axes. There are different pyramids, depending upon vary ing axial intercepts. There are, further, two independent types of

Monoclinic Pyramids.

monoclinic pyramids, depending upon whether the two faces on the upper half of the crystal intersect the positive or the negative end of the a axis. A unit pyramid of the first of these types is shown in Fig. 169 and has for its symbol (111). A unit pyramid of the second of these types is represented in Fig. 170 and has for its symbol (Ill). Fig. 171 shows these two types in combination with each other. It should be emphasized that a monoclinic pyramid consists of only four faces, two of which are to be found intersecting the upper end of the c axis and the other two inter secting its lower end. The two types described above are entirely independent of each other.

2. Prism. The monoclinic prism has four vertical faces, each of which intersects the a and b axes. There are various prisms with different axial intercepts. A unit prism is represented in Fig. 172 and has for its symbol (110).

3. Orlhodome. An orthodome consists of two parallel faces, each of which intersects the a and c axes and is parallel to the b or ortho-

Monoclinic System

axis. Its name is derived from that of the axis to which it is parallel. There are different orthodomes with different axial intercepts. There are also two distinct and independent types of orthodomes, depending upon whether the face upon the upper end of the crystal intersects the positive or negative end of the a axis. These two types of orthodomes are represented in combination in Fig. 173, but it should be emphasized that they are entirely inde pendent of each other. The symbol of the unit orthodome in front is (101) and that of the one behind is (101).

Orthopinacoid.

4. Clinodome. The clinodome is a form having four faces, each of which intersects the b and c axes and is parallel to the a or clinoaxis. There are various clinodomes with differing axial intercepts. A unit form is represented in Fig. 174 and would have for its symbol (Oil).

5. Orthopinacoid. The orthopinacoid has two parallel faces, each of which intersects the a axis and is parallel to the b and c axes. It derives its name from the fact that it is parallel to the b or ortho-axis. It is represented in Fig. 174 and its symbol is (100).

6. Clirwpinacoid. The clinopinacoid consists of two parallel faces, each of which intersects the b axis and is parallel to the a (clino) and the c axes. It is represented in Fig. 173 and its symbol is (010).

7. Basal Pinacoid. The basal pinacoid is a form consisting of two parallel faces, each of which intersects the vertical axis and is

Manual Of Mineralogy

parallel to the a and b axes. It is represented in Fig. 172 and its symbol is (001).

It should be noted that the only monoclinic form that is abso lutely fixed in its designation is the clinopinacoid. The other forms may vary with a variation in the choice of the directions of the a

Fig. 175. Fig. 176.

Pyroxene.

Fig. 177.

Fig. 178.

Amphibole.

Gypsum.

Fig. 181. Fig. 182.

Orthoclase.

and c axes. For instance the orthopinacoid, basal plane and orthodome maybe converted into each other by a change in orienta tion and the same is true of the prism, pyramid and clinodome.

Monoclinic Combinations. Characteristic combinations of the forms described above are given in Figs. 175-182.

Triclinic System

Characteristics of Monoclinic Crystals

Monoclinic crystals are to be distinguished chiefly by their low symmetry. The fact that they possess but one plane of sym metry and one axis of binary symmetry at right angles to it would serve to differentiate them from the crystals of all other systems and classes. Usually the inclination of the crystal faces which are parallel to the clino-axis is marked.

X. Triclinic System

Crystallographic Axes. The crystallographic axes of the Triclinic System are three in number. They are of unequal lengths and make oblique angles with each other. The axial directions for each triclinic mineral are chosen arbitrarily, but in such a way as to yield the simplest relations. Any one of them may be taken as c, the vertical axis. The longer of the other two is designated as the b or macro-axis, while the shorter is called a or the brachy-axis. The relative lengths of the three axes and the angles which they make with each other have to be calculated for each mineral from appropriate measurements. The angles which the different axes make with each other are designated respectively as a, 0 and y (see Fig. 183). For example, the crystal constants of the triclinic mineral axinite are as follows: a :b :c 0.492 : 1 : 0.480; a 82° 54'; p 91° 52'; y 131° 32'.

Normal Class

Symmetry and Forms. The symmetry of the Normal Class of the Triclinic System consists only in a center of symmetry (see Fig. 7, page 11). It has no axes or planes of symmetry. All forms of the Triclinic System consist of two similar and parallel faces. In this respect all triclinic forms might be spoken of as pinacoids. They are, however, usually designated as pyramids when their faces intersect all three axes, as prisms or domes when they inter sect two axes and as pinacoids when they intersect but one axis. It is to be noted, however, that by a change in the choice of axial directions any one of these forms could be converted into any other.

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1. Pyramid. A tri clinic pyramid consists of two parallel faces, each of which intersects all three crystallographic axes. There are four possible types, depending upon the octants in which the faces lie. Fig. 184 shows a combination of four unit pyramids.

Fig. 183. Triclipic Axes.

Fig. 184. Fig. 185.

Pyramids. Prisms and Basal Pinacoid.

2. Prisms. A triclinic prism consists of two parallel faces, each of which intersects the a and b axes and is parallel to the c axis. There are two possible types, a combination of which is shown in Fig. 185.

3. Domes. A triclinic dome consists of two similar parallel faces, each of which intersects the c axis and either the a or b axes

Macrodomes and Brachydomes and Macropinacoid, Brachypin-

Brachypinacoid. Macropinacoid. avoid, and Basal Pinacoid.

and is parallel to the other. They are spoken of as either macro- or brachydomes, depending upon the axis to which they are parallel. There are two types of each. Fig. 186 represents a combination of the two types of macrodome and Fig. 187 a combination of the two brachydomes.

4. Pinacoids. A triclinic pinacoid is a form consisting of two parallel faces, each of which intersects one crystallographic axis

Triclinic System

and is parallel to the other two. They are designated as the macropinacoid with the symbol (100), as the brachypinacoid with the symbol (010), and as the basal pinacoid with the symbol (001). A combination of the three forms is shown in Fig. 188.

Triclinic Combinations. Figs. 189-191 represent characteristic triclinic crystals.

Characteristics of Triclinic Crystals

There are only a few triclinic minerals and they seldom show distinct and well-developed crystals. When such crystals do occur they are to be recognized by the fact that they have no plane or axis of symmetry and by the fact that each form consists of only two similar and parallel faces.

Ii. General Physical Properties Of Minerals

I. Structure Of Minerals

If by the phrase "structure of minerals" is meant their internal or molecular structure, all minerals may be included in one of two classes: (1) Crystalline; (2) Amorphous. With only a few excep tions, minerals are crystalline in their structure. This does not signify, however, that these minerals necessarily occur in distinct crystals, but only that their internal structure is such that they may under favorable circumstances definitely crystallize. The few mineral species that are classified as amorphous possess no regular internal structure and therefore cannot crystallize.

Commonly, however, the expression "structure of minerals" refers to their outward shape and form. Various descriptive terms are used in this connection that will need short definitions.

1. When a mineral consists of distinct crystals the follow ing terms may be used:

a. Crystallized. In definite crystals (see A, pi. II)

b. Acicular. In slender needlelike crystals.

c. Capillary. In hairlike crystals.

d. Filiform. In threadlike crystals.

e. Dendritic. Arborescent, in slender divergent branches, somewhat plantlike, made up of more or less distinct crystals.

f. Reticulated. Latticelike groups of slender crystals.

g. Divergent or Radiated. Radiating crystal groups (see C, pi. II).

h. Drusy. A surface is drusy when covered with a layer of very small crystals.

2. When a mineral consists of columnar individuals the following terms may be used :

a. Columnar. In stout columnlike individuals.

b. Fibrous. In slender columnar individuals. The fibers may be parallel or radiated (see D, pi. II).

Plate Ii.

A. Crystallized — Quartz.

B. Stalac title — Litnonite.

C . Radiated — Natrolite.

D. Fibrous — Serpentine.

Plate Iii.

t

B.

A. Mammillary or Reniform — Hematite. B. Botryoidal — Chalcedony. C. Concentric — Malachite.

Structure Of Minerals

c. Stellated. When the radiating individuals form starlike or circular groups.

d. Globular. When the radiating individuals form spherical or hemispherical groups.

e. Botryoidal. When the globular forms are in groups. The word is derived from the Greek for a "bunch of grapes" (see B

pi. III).

f. Reniform or Mammillary. When a mineral is in broad rounded masses resembling hi shape either a kidney or mammal (see A, pi. III).

3. When a mineral consists of scales or lamallae.

a. Foliated. When a mineral separates easily into plates or leaves.

b. Micaceous. Similar to foliated but the mineral can be split into exceedingly thin sheets, as in the micas.

c. Lamellar or tabular. When a mineral consists of flat platelike individuals superimposed upon and adhering to each other.

d. Plumose. Consisting of fine scales with divergent or feather like structure.

4. When a mineral consists of grains.

Coarse to fine granular. When a mineral consists of an aggregate of large or small grains.

5. Miscellaneous.

a. Compact — Earthy. A uniform aggregate of exceedingly minute particles.

b. Stalactitic. When a mineral has the shape of cylinders or cones which have been formed by deposition from mineral-bearing waters dripping from the roof of some cavity (see B, pi. II).

c. Concentric. Consisting of more or less circular layers super imposed upon one another about a common center (see C, pi. III).

d. Banded. When a mineral occurs in narrow parallel bands of different color or texture.

e. Geodes. When a cavity has been lined by the deposition of mineral material but not wholly filled, the more or less spherical mineral shell is called a geode. The mineral is often banded owing to successive depositions of the material, and the inner surface is frequently covered with projecting crystals.

Manual Of Mineralogy

f. Massive. When a mineral is composed of compact material with an irregular form and does not show any peculiar structure like those described above, it is said to be massive.

Ii. Cleavage, Parting And Fracture

1. Cleavage. If a mineral, when the proper force is applied, breaks so that it shows definite plane surfaces, it is said to possess a cleavage. These cleavage surfaces resemble natural crystal faces. They are always parallel to some possible crystal face, and usually to one having simple relations to the crystallographic axes. They may be perfect, as in the cases of the micas, calcite, gypsum, etc., or they may be more or less obscure. Cleavage is due to the fact that in the mineral structure there is a certain plane or planes perpendicular to which the molecular cohesion is weaker than in other directions. All minerals do not show cleavage, and only a

comparatively few show it in an eminent degree. The quality of the cleavage and its crystallographic di rection are often important aids in the identification of a mineral. The cleavage of a mineral is described'ac-

cording to the crystal face to which

itisjarailel, as cubic cleavage (galena,

halite) (see Fig. 192), octahedral cleavage (fluorite), dodecahedral

Fig. 192. Cubic Cleavage — Galena.

cleavage (sphalerite), rhombohedral cleavage (calcite), prismatic cleavage (amphibole), basal cleavage (topaz), pinacoidal cleavage (stibnite), etc.

2. Parting. Certain minerals when subjected to a strain or pressure develop planes of molecular weakness along which they may subsequently be broken. Crystals may also contain twinning lamellae along whose surfaces the crystal may break. When plane surfaces are produced on a mineral in this way it is said to have a parting. This phenomenon resembles cleavage, but is to be distinguished from it by the facts that not every specimen of a certain mineral will exhibit it, but only those specimens which

Hardness Of Minerals

have been subjected to the proper pressure, and that even in these specimens there are only certain planes in the given direction along which the mineral will break. In the case of cleavage, every specimen of the mineral will in general show it, and it can be pro duced in a given direction in all parts of a crystal. Familiar ex amples of parting are the cases of the octahedral parting of mag netite, the basal parting of pyroxene and the rhombohedral parting of corundum.

3. Fracture. By the fracture of a mineral is meant the way in which it breaks when it does not show plane surfaces as in cleavage or parting. The following terms are commonly used to designate different sorts of fracture:

a. Canchoidal. When the fracture has smooth, curved surfaces like the interior surface of a shell it is said to be conchoidal (see Fig.

193). This is most com monly observed in such sub stances as glass, quartz, etc.

b. Fibrous or Splintery.

"When the mineral breaks showing splinters or fibers.

c. Hackly. When the mineral breaks with a jagged, irregular surface wTith sharp edges.

d. Uneven or Irregular. When the mineral breaks into rough and irregular surfaces.

m. HARDNESS OF MINERALS

Minerals vary quite widely in their hardness, and a determina tion of their degree of hardness is often an important aid to their identification. A series of minerals has been chosen as a scale by comparison with which the relative hardness of any mineral may be told. The scale consists of crystallized varieties of the following minerals, each species being harder than those preceding it in the scale.

Fig. 193. Conchoidal Fracture — Vol canic Glass.

Manual Of Mineralogy

1. Talc.

2. Gypsum.

3. Calcite.

Scale of Hardness.

4. Fluorite. 8. Topaz.

5. Apatite. 9. Corundum.

6. Orthoclase. 10. Diamond.

7. Quartz.

In order to determine the relative hardness of any mineral in terms of this scale, it is necessary to find which ones of these minerals it can and which it cannot scratch. In making the determination the following precautions should be observed: Sometimes when a mineral is softer than another, portions of the first will leave a mark on the second which may be mistaken for a scratch. It can be rubbed off, however, while a true scratch will be permanent. Some minerals are frequently altered on the surface to material which is much softer than the original mineral. A fresh surface of the specimen to be tested should therefore be used. Sometimes the physical structure of a mineral may prevent a cor rect determination of its hardness. For instance, if a mineral is pulverulent, granular or splintery in its structure, it may be broken down and apparently scratched by a mineral much softer than it self. It is always advisable when making the hardness test to confirm it by reversing the order of procedure.

The following materials may serve in addition to the above scale: The finger nail is a little over 2 in hardness, since it can scratch gypsum and not calcite. A cent is about 3 in hardness, since it can just scratch calcite. The steel of an ordinary pocketknife is just over 5, and ordinary window glass has a hardness of 5.5.

Crystals frequently show different degrees of hardness, depend ing upon the direction in which they are scratched. Ordinarily the difference is so small that it can be detected only by the use of delicate instruments.

Iv. Tenacity Of Minerals

The following terms are used to describe various kinds of tenacity in minerals:

1. Brittle. When a mineral breaks or powders easily.

Specific Gravity Of Minerals

2. Malleable. When a mineral can be hammered out into thin sheets.

3. Sectile. When a mineral can be cut into thin shavings with a knife.

4. Flexible. WTien a mineral bends but does not resume its original shape when the pressure is released.

5. Elastic. When, after being bent, the mineral will resume its original position upon the release of the pressure.

V. Specific Gravity Of Minerals

The specific gravity of a mineral is a number which expresses the ratio existing between its weight and the weight of an equivalent volume of water. If a mineral has a specific gravity of 2, it means that a given specimen of that mineral weighs twice as much as the same volume of water. The specific gravity of a mineral which does not vary in its composition is a constant factor, the deter mination of which is frequently an important aid to its identifica tion.

After a little experience one can frequently judge quite accu rately the specific gravity of a mineral by weighing it in the hand. Minerals containing the heavy metals like lead, copper, iron, etc., can be at once differentiated from those containing lighter ele ments by this means. And by practice one can become expert enough to be able to distinguish from each other minerals that have comparatively small differences in specific gravity; for instance, topaz (sp. gr. 3.52) from orthoclase (sp. gr. 2.57), and fluorite (sp. gr. 3.18) from quartz (sp. gr. 2.6).

In order to accurately determine the specific gravity of a min eral, the following conditions must be observed: The mineral must be pure. It must also be solid, with no cracks or cavities within wliich bubbles or films of air could be imprisoned. The fragment used should be reasonably large, about one cubic inch being a con venient size. If these conditions cannot be met, it is of little use to attempt a specific gravity determination by any rapid and simple method.

The necessary steps in making an ordinary specific gravity

Manual Of Mineralogy

determination are briefly as follows: The mineral is first weighed in air. Let this weight be represented by x. It is then immersed in water and weighed again. Under these conditions it weighs less, since any object immersed in water is buoyed up by a force equiva lent to the weight of the water displaced. Let the weight in water be represented by y. Then x — y equals the loss of weight caused by immersion in water, or the weight of an equal volume of water.

The expression - will therefore yield a number which is the

x — y

specific gravity of the mineral.

The specific gravity of a mineral may be determined in various ways, those most commonly used being described below.

1. By Means of a Chemical Balance. The most accurate method of determining the specific gravity of a mineral is by the use

of a chemical balance. To one beam of the balance is suspended a wire basket which is so arranged that it can be immersed in a beaker of water (see Fig. 194). The basket is hung in the water and then counterbalanced by weights on the opposite pan of the balance. The mineral specimen to be tested, having been first weighed on the balance in the ordinary fashion, is now placed in the basket under the water and weighed again. These two weights are the necessary data for calculat ing the specific gravity as explained above.

2. By Means of a Jolly Balance.

Fig. 195 represents the balance of Jolly, by which the specific gravity is measured through the stretching of a spiral wire spring. From the spring is suspended two small metal pans (c and d), one above the other. The ap paratus is so arranged that the lower pan ( d ) is always immersed in

Specific Gravity Of Minerals

a beaker of water which, resting upon the adjustable platform B, can be placed at any required height. On the side of the upright A, which faces the spiral wire, there is a mirror with a graduated scale engraved upon it. The position of the balance is determined by means of a small bead (m) which is strung on the wire above the upper pan and which serves as an indicator, into such a position that the bead exactly covers its image in the mirror, and its posi tion is then determined by means of the scale.

Three readings must be taken: first, simply the position of the balance with the lower pan in the water, x; second, its position when the mineral is placed in the upper pan, y; and third, its position when the mineral is in the lower pan and covered with water, z. The platform B with the beaker of water must be properly adjusted for each of these read ings so as to always have the lower pan im mersed in the water. The expression x — y will give a number representing the weight of the mineral in air, while x — z will yield a number corresponding to its weight in water.

From these values the specific gravity of the mineral can be calculated as described above.

3. By Means of a Beam Balance. This is a very convenient and quite accurate method of determining specific gravity. The balance illustrated in Fig. 196 was devised by S. L. Penfield, who describes its operation as follows:

"The beam of wood is supported on a fine wire, or needle, at b and must swing freely. The long arm be is divided into a decimal scale, commencing at the fulcrum 6; the short arm carries a double arrangement of pans so suspended that one of them is in the air and the other in water. A piece of lead on the short arm serves to almost balance the long arm, and, the pans being empty, the beam is brought to a horizontal position, marked upon the upright, near c, by means of a rider d. A number of counterpoises are needed,

The eye is brought

Fig. 195.

Manual Of Mineralogy

which do not have to be of any specific denomination, as it is their position on the beam and not their actual weight which is recorded. The beam being adjusted by means of the rider d, a fragment of the mineral is placed in the upper pan and a counterpoise is chosen, which, when placed near the end of the long arm, will bring it into a horizontal position. The weight of the mineral in air is given by the position of the counterpoise on the scale. The mineral is next

transferred to the lower pan, and the same counterpoise is brought nearer the fulcrum b until the beam becomes again horizontal, when its position gives the weight of the mineral in water." From these two values the specific gravity of the mineral can be calcu lated.

Vi. Properties Depending Upon Light

A. Luster

The luster of a mineral is its appearance due to the effect of light upon it. In general we divide minerals into three classes depending upon their luster, namely, metallic luster, submetallic luster and nonmetallic luster. A mineral having the appearance of a metal like lead or copper is said to have a metallic luster. The term is further defined by saying that a mineral with a metallic luster is strictly opaque to light when examined on its thinnest edges. The metallic luster of a mineral can be proved by observing the color of its powder. If the powder is black or very dark in color, it means that each little particle of the mineral is still opaque to

Properties Depending Upon Light 73

light, and therefore the mineral has a metallic luster. This test is made usually by the aid of what is called a streak plate. This consists of a piece of unglazed white porcelain upon which the mineral is rubbed so that a streak of its powder is formed upon the plate. The color of this "streak" of the mineral, as it is called, will determine its luster and also frequently will materially help in its identification. Examples of minerals with metallic luster would be, galena, PbS, with a bluish gray streak ; pyrite, FeS2, with a black streak; chalcopyrite, CuFeS2, with a greenish black streak; and hematite, Fe203, with a dark reddish brown streak.

Nonmetallic Luster. Minerals with a non metal lie luster are transparent to light on their thin edges. In general they are light colored, but not necessarily so. When a streak is obtained from a nonmetallic mineral, it is either colorless or very light in color. Various descriptive terms are used to further describe the ap pearance of nonmetallic minerals, the more common being as follows:

Vitreous. Having the luster of glass. Example, quartz.

Resinous. Having the appearance of resin. Example, sphal erite.

Pearly. Having the iridescent appearance of a pearl. This is usually observed in minerals on surfaces that are parallel to cleav age planes. Example, basal plane on apophyllite.

Greasy. Looking as if covered with a thin layer of oil. Ex amples, some specimens of sphalerite and massive quartz.

Silky. Like silk. It is the result of a fine fibrous structure. Examples, fibrous malachite, serpentine, etc.

Adamantine. Having a hard, brilliant luster like that of a diamond. It is due to the mineral's high index of refraction (see p. 77). The transparent lead minerals, like cerussite and anglesite, show it.

Submetallic Luster. There is no sharp divisional line be tween minerals with metallic and those with nonmetallic luster, and the group of minerals lying between is said to have a submetallic luster. They show a colored streak, but one which is not black or very dark in color. Examples of minerals with submetallic luster are limonite and some of the darker varieties of sphalerite.

Manual Of Mineralogy

B. Color of Minerals

The color of minerals is one of their most important physical properties. In the case of many minerals, especially those showing a metallic luster, color is a definite and constant property and will serve as an important means of identification. For example, the brass-yellow color of chalcopyrite, the blue-gray of galena, the black of magnetite, the green of malachite, etc., is in each case a striking property of the mineral. It is to be noted, however, that surface alterations may change the color even in minerals whose color is otherwise constant. This is shown in the yellow tarnish frequently observed on pyrite and marcasite, the purple tarnish on bornite, etc. In noting the color of a mineral, therefore, a fresh surface should be examined. Many minerals, however, do not show a constant color in their different specimens. This variation in color in the same species may be due to different causes. A change in color is often produced by a change in composition. The pro gressive isomorphous replacement of zinc by iron in sphalerite (see page 84) will change its color from white through yellow and brown to black. The minerals of the Amphibole Group show a similar variation in color. The amphibole tremolite, which is a silicate with only calcium and magnesium as bases, is very light in color, at times almost white; while actinolite and hornblende, which are amphiboles that contain increasing amounts of iron, range in color from green to black. Again, a mineral may show a wide range of color without any apparent change in composition. Fluorite is a striking example of this, since it is found in crystals that are colorless, white, pink, yellow, blue, green, etc. Such extreme cases are, however, rare. Minerals are also frequently colored by various impurities. The red variety of quartz, known as jasper, is colored by small amounts of hematite. From the above it is seen that, while the color of a mineral is one of its im portant physical properties, it is not always constant, and must therefore often be used with some caution in the identification of a species.

Play of Colors. Iridescence, Opalescence, etc. A mineral

is said to show a play of colors when on turning it several prismatic

Properties Depending Upon Light 75

colors are seen in rapid succession. This is to be seen especially in the diamond and precious opal. A mineral is said to show a change of color when on turning it the colors change slowly, being different for varying positions. This is observed in labradorite. A mineral is iridescent when it shows a series of prismatic colors in the interior of the crystal or on the surface. It is usually caused by the presence of small fractures or cleavage planes which serve to break up the light into the prismatic colors. Opalescence is a milky or pearly reflection from the interior of a specimen. It is observed at times in opal and cat's-eye. A mineral is said to show a tarnish when the color of the surface differs from that of the interior.

Asterism. Some crystals, especially those of the Hexagonal System, when viewed in the direction of the vertical axis, present starlike rays of light. This arises from peculiarities of texture along the axial directions, or from some inclusions. A remarkable example is the star sapphire.

Phosphorescence. Several minerals when rubbed or heated give out light. This property is known as phosphorescence. Fluorite often shows phosphorescence when fragments are gently heated. The color of the emitted light may be green, purple, rose, yellow, etc.

C. Refraction of Light in Minerals

When light comes into contact with a transparent mineral, part of it is reflected from the surface of the mineral and part enters the mineral. The light which enters the mineral is in general re fracted. When light passes from a rarer into a denser medium, as in the case of passing from air into a mineral, its velocity is retarded. This change in velocity is accompanied by a corresponding change in the direction in which the light travels, and it is this change in direction of propagation that is known as refraction of light. The amount of refraction of a given light ray is directly proportional to the ratio existing between the velocity of light in air and in the mineral. The ratio between these two velocities is known as the index of refraction of the mineral and is designated by n. That is, if the index of refraction, or n, of a mineral is 2, light will travel in it with one-half the velocity it has in air.

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In Fig. 197 let M-M represent the surface of a crystal of fluorite. Let N-0 be normal to that surface. Let A-0 be one of a number of parallel light rays striking the surface M-M in such a way as to make the angle i (angle of incidence) with the normal N-O. Let 0-P be at right angles to the rays and representing the wave front of the light in air. As the crystal is the denser medium the light will travel in it more slowly. Therefore, as each ray in turn strikes the surface M-M, it will be retarded and the direction of its path be changed proportionately. In going from a rarer into a denser

medium, the direction of the ray will be bent toward the normal N-0. To find the direction of the rays and line of wave front in the crystal, proceed as follows: Since the index of refraction of fluorite is 1.43, ray A will travel in the crystal, in the time it takes ray C to

travel from P to R, of that distance, or to some point on the circular arc the length of whose radius OA' is — the distance

P-R. Similarly, ray B will travel in the mineral during the period of time in which ray C travels from S to It a distance equal to yyy

of the distance S-R, or the radius TB'. The same reasoning will hold true for all other rays. The wave front in the crystal can then be determined by drawing a tangent — the line A'B'R to these

Properties Depending Upon Light

various circular arcs; and lines perpendicular to this wave front will represent the direction in which the light travels in the mineral, and the angle NOA' or r will be the angle of refraction. Fig. 198 shows the same construction as that of Fig. 197, only in this case the mineral in question is assumed to be diamond. Since the index of refraction of diamond (n 2.42) is much greater than that of fluorite, light will travel in it with a still slower velocity. Conse quently in diamond the amount of refraction will be greater. This is shown in the two figures, in both of which the angle of incidence is the same.

The refractive power toward light which a mineral possesses has often a distinct effect upon the appearance of the mineral. For example, a mass of cryolite may almost always be told at sight, though, as is generally the case, there is no crystal shape to aid in the identification. The mass has a peculiar appearance, something like that of wet snow, and quite different from that of ordinary white substances; and this is due to the fact that the index of re fraction of cryolite is unusually low for a mineral. An instructive experiment may be tried by finely pulverizing some pure white cryolite and throwing the powder into water, when it will appar ently disappear, as if it had instantly gone into solution. The powder, however, is insoluble, and may be seen indistinctly as it settles to the bottom of the vessel. The reason for this disappear ance of the cryolite is that its index of refraction (about 1.34) is near that of water (1.335), hence the light travels almost as readily through the mineral as through water, and consequently it under goes little reflection or refraction.

Substances having an unusually high index of refraction have an appearance which it is hard to define, and which is generally spoken of as adamantine luster. This land of luster may be com prehended best by examining specimens of diamond ( n 2.419) or of cerussite (n about 3.2). They have a flash and quality, some diamonds almost a steel-like appearance, which is not pos sessed by minerals of low index of refraction; compare, for example, cerussite and fluorite (n 1.434). It is their high index of re fraction that gives to many gem minerals their great brilliancy and charm.

78 Manual Of Mineralogy

In the majority of cases the index of refraction of a mineral is not far from 1.5, and gives to minerals a luster which is designated as vitreous. Quartz (n 1.55), feldspar (n 1.52) and calcite (n 1.57) are good examples.

D. Double Refraction in Minerals

All minerals except those belonging to the Isometric System show in general a double refraction of light. That is, when a ray of light enters such a mineral it is broken up into two rays, each of

-.It

' 1

" - n

Wm 1

fafl

Fig. 199. Double Refraction in Calcite.

which travels with a different velocity through the mineral. Since each ray has its own characteristic velocity, it follows that the angle of refraction will be different in each case and the paths of the two rays will be divergent. In other words, the light has undergone double refraction. In the majority of cases the amount of this double refraction is small, and the fact that it exists can only be demonstrated by special and delicate instruments. Calcite, how ever, shows such a strong double refraction that it can be easily observed. Take a cleavage block of clear calcite (Iceland spar), for instance, and place it over an image marked on paper. The image will appear double (see Fig. 199).

The amount of double refraction, or in other words the amount of divergence of the two rays, shown by any mineral depends, first, upon the refracting power of the mineral, or its strength of bire-

Pyroelectricity

fringence, as it is called; second, upon the thickness of the block of the mineral; and lastly, upon the crystallographic direction in which the light is traveling in the mineral. In the case of tetragonal and hexagonal minerals, there is one direction (that of the vertical crystallographic axis) in which no double refraction takes place. As soon as a ray of light in the mineral diverges from this direction it is doubly refracted, and the amount of double refraction in creases as the path of the light becomes more oblique, and attains its maximum when it is at right angles to the vertical axis. Such minerals belong to the optical class known as uniaxial. In the case of orthorhombic, monoclinic and triclinic minerals, there are two directions similar to the one described above, in which no double refraction takes place, and the minerals of these systems are there fore spoken of as optically biaxial.

In addition to doubly refracting light, all minerals except those of the Isometric System polarize it as well. Ordinary light is conceived as made up of vibrations taking place in all planes. Light is polarized when it vibrates in a single plane. In the case of both uniaxial and biaxial crystals, each of the two rays into which a beam of light is refracted is polarized and in planes which are perpendicular to each other. For a fuller consideration of the opti cal properties of minerals, the reader must be referred to books of a more detailed character.

Vii. Pyroelectricity

Crystals of certain minerals, on cooling after being heated to about 100° C., will develop upon different portions a positive and a negative electric charge. This can be proved by the power that such minerals showr under these conditions to attract and hold to themselves small pieces of paper, etc. Minerals which are hemimorphic in their crystallograpliic character, like calamine, tourma line, etc., exhibit this property.

Iii. Chemical Mineralogy

A mineral may be defined as a naturally occurring substance having a definite chemical composition. The chemical composition of a mineral is the most fundamentally important fact about it, for upon this all its other properties must in great measure be de pendent. It should be added that the characters of a mineral depend upon not only the chemical nature of its ultimate particles but very definitely also upon the arrangement of these particles in the crystalline structure. The physical characteristics of a mineral may sometimes serve as means of its positive identification, and in the great majority of cases they will be of material assistance; but the final proof of its identity will more often lie in the deter mination of its chemical character by means of chemical tests. Consequently the study of the chemistry of minerals is the most important single division of the subject. This section will, there fore, be devoted to a brief and elementary discussion of chemical mineralogy. First some general aspects of the subject 'will be presented, followed by a short description of the methods of testing for the different elements most commonly observed. The scope and size of this book necessitate the assumption that the reader is familiar with at least the essentials of chemical fact and nomen clature.

Scientists up to the present time have established the occurrence of more than eighty different elements. The greater part of these, however, are extremely rare and are only of scientific interest. Some forty-four elements are found in sufficient amount, or because of their properties are of sufficient importance, to warrant a discus sion of them here. A considerable proportion of this list also must be considered as rare in occurrence. The following table gives the names and symbols of the eighteen most common elements ar ranged in the approximate order of their importance as constituents of the earth's crust:

Chemical Groups

Oxygen

Sodium

Na.

Phosphorus

P.

Silicon

Si.

Potassium

K.

Sulphur

S.

Aluminum

Al.

Hydrogen

H.

Barium

Ba.

Iron

Fe.

Titanium

Ti.

Manganese

Mn.

Calcium

Ca.

Carbon

Strontium

Sr.

Magnesium

Mg.

Chlorine

Fluorine

F.

It is to be noted that the above list fails to include such important elements as copper, lead, zinc, silver, gold, tin, mercury, nickel, antimony, arsenic, etc., all of which form much less than onehundredth of one per cent of the rocks of the earth's crust.

These elements occur alone or in various chemical combinations in the form of minerals. Below is given a brief discussion of the various classes of chemical compounds in which the majority of minerals occur.

Chemical Groups

Elements. There are a few minerals that consist of single elements alone. For example, gold, Au.

Sulphides. A very important group of minerals, consisting of combinations of the various metals with the element sulphur, are known as sulphides. They include the majority of the metallic ore minerals. For example, pyrite, FeS2.

Sulpho-salts. This group of minerals includes a series which mostly contain lead, copper or silver in combination with sulphur and either antimony or arsenic. For example, tetrahedrite, Cu8Sb2S7.

Haloids. This group includes minerals that are salts of the halogen acids, chiefly hydrochloric or hydrofluoric acids. Ex amples are halite, NaCl, and fluorite, CaF2.

Oxides. The minerals of this group contain a metal in com bination with oxygen. For example, hematite, Fe203.

Hydroxides. An hydroxide is a mineral that contains the hydroxyl group, OH, as an important radical. For example, limonite,

Carbonates. The carbonates are salts of carbonic acid, H2C03. For example, calcite, CaC03.

Manual Of Mineralogy

Silicates. The silicates form the largest chemical group among minerals. They contain various elements as bases, the most com mon of which are sodium, potassium, calcium, magnesium, alu minum and ferrous and ferric iron. They are frequently very com plex in their chemical structure. They are salts of a number of different silicic acids, the most important of which are as follows:

Orthosilicate acid H4Si04, which is represented by almandite,

Metasilicic acid H4Si206 or H2Si03, represented by leucite,

Polysilicic acid H4Si308, represented by orthoclase, KAlSi308.

Niobates and Tantalates. These are combinations of various metals with the rare niobic and tantalic acids. For example, columbite, FeNb206, and tantalite, FeTa206.

Phosphates. The phosphates are salts of some phosphoric acid. The most common member of the group is the mineral apatite,

Sulphates. The sulphates are salts of sulphuric acid, H2S04. For example, gypsum, CaS04.2H20.

Tungstates. These are salts of the rare tungstic acid H2W04. For example, scheelite, CaW04.

Derivation of a Chemical Formula from the Analysis of

a Mineral

The chemical formulas which are assigned to minerals have in every case been calculated from chemical analyses. An analysis gives the percentage composition of a mineral, or, in other words, the parts by weight in one hundred of the different elements or radicals present. Consider the following analysis of chalcopyrite :

Percentages

S 34.82 Cu 34.30 Fe 30.59

Atomic weights

Ratio

1.086 2.00 0.539 0.99 or 1.00 0.547 1.00

The percentage numbers given indicate the proportions by weight of the different elements in the mineral. But as these elements

Calculation Of The Percentage Composition 83

have different atomic weights, the numbers do not represent the ratio of the different atoms to each other in the chemical molecule. In order to derive the relative proportions of the atoms of the different elements to each other, the percentages as given are divided in each case by the atomic weight of the element. This gives a series of numbers which does represent the ratio of the atoms to each other in the molecule. In the analysis of chaleopyrite this ratio becomes S : Cu : Fe 2 : 1 : 1. Consequently CuFeS2 will constitute the chemical formula for the mineral.

If the mineral is an oxygen compound the results of the analysis are given as percentages of the oxides present, and by a calculation similar to that outlined above the ratio of these oxide radicals to each other in the molecule is determined; the only difference in the process being that in this case the percentage numbers are divided by the sum of the atomic weights of the elements present in the different radicals. As an example consider the following analysis of gypsum:

Percentages

SO, 46.61 CaO 32.44 II20 20.74

From this it is seen that the ratio of the radicals to each other in the molecule is S03 : CaO : H20 1:1:2, and consequently the composition of gypsum can be represented by the formula CaO.S03. 2H20 or CaS04.2H20.

Molecular weights Ratio

83.06 0.583 1.00

56.1 0.578 0.99 or 1.00

18.0 1.152 1.98 or 2.00

Calculation of the Percentage Composition of a Mineral from Its Chemical Formula

It frequently happens that it is desirable to determine what the theoretical composition of a mineral is, having given its formula. The process of calculation is the reverse of that described in the preceding division. Take,- for example, the mineral chalcopyrite, CuFeS2; what are the proportions by weight of the different ele ments in one hundred parts of the mineral? The process consists in first adding up the atomic weights of the different elements pres-

Manual Of Mineralogy

ent and so obtaining the molecular weight of the compound, as follows:

Atomic weights

Cu 63.6

Fe 55.9

S 32.06 X 2 64.12 Molecular weight CuFeSi 183.62

It is obvious from the above that in 183.62 parts by weight of chalcopyrite there are 63.6 parts of copper, etc. In order to find the parts of copper in 100 parts of the mineral, or in other words, its percentage, the following proportion is made :

183.62 : 63.6 100 : x.

When this equation is solved, x becomes 34.64, or the percentage of copper in chalcopyrite. The percentages of the iron and sulphur are to be obtained in a similar manner.

Isomorphism

It is to be noted frequently that the results of a mineral analysis do not agree with the theoretical composition of the mineral as calculated from its formula. Further, it often happens that the analyses of different specimens of the same mineral will show marked variations in the proportions of the different elements present. If the material analyzed was pure and the analysis accurately made, these variations are commonly to be explained by the principle of isomoryhim, (derived from two Greek words mean ing "same'' and "form"). To make clear what is meant by this term, it will be best to consider some illustrative examples. Sghalerite, for instance, is a mineral which shows in its different speci mens a wide range in color, from white through brown to black,

At. Rawt. tio.

At. Rawt. tio.

At. Rawt. tio.

S =32,22 Zn =67.40 Fe .

32.06=1.00 65.4 =1.03

32.06=1.04 =1.00 65.4 =0.96 1 m

55.9 =0.06 )

32 06=1.037 =1.0 65.4 0.7641

55.9 =0.276 I.

112.4 0.002 1 1 010

206.9 =0.004 J

Cd .

Pb .

Total 99. 68

Isomorphism

with a corresponding variation in composition. In column I is given an analysis of white sphalerite from Franklin Furnace, N. J., in column II is given an analysis of a brown sphalerite from Roxbury, Conn., and hi column III that of a black sphalerite from Felsobanya, Rumania.

It will be noted that in the three analyses there is a progressive increase in the percentages of iron present and a corresponding decrease in the amount of zinc. It would appear as if the iron had replaced a portion of the zinc in the mineral and was playing the same part as the zinc in the molecule. Further, if the atomic ratios are derived from each analysis by the method described in the preceding division, it will be found that in analyses II and III the series of numbers do not show any rational relations to each other. But, if the numbers derived in each case from the per centages of the different metals present are combined, their sum will equal the number derived from the percentage of the sulphur. In other words, the number of atoms of zinc plus those of iron, lead, and cadmium equals the number of atoms of sulphur. The for mula of sphalerite could therefore be written R"S, where R" equals chiefly zinc, with smaller amounts of iron and other metals. Another way of expressing the same thing would be Ip this case the iron is said to be isomorphous with the zinc since-it. has the power to replace the zinc in the mineral in varying nronortions without changing its molecular structure or crystal form

The garnets form a series of minerals with the same crystalliza tion and general physical properties, but show quite a wide varia tion in chemical composition. Consider the following analysis of an almandine garnet :

Percentages

Molecular weights

Ratio

Si02

35.92

0.594

3.00

19.18

-4- 102.2

0.187-

► 0.217 1.09

Fe203

4.92

-4- 159.8

0.030

FeO

29.47

-4- 71.9

0.409

MnO

4.80

-4- 71.0

0.067

0.609 3.02

MgO

3.70

-4- 40.36

0.091

CaO

2.38

0.042

Manual Of Mineralogy

It is a silicate containing chiefly ferrous and aluminum oxides but with smaller amounts of manganese, magnesium, calcium and ferric oxides. If the ratio of the series of oxides to each other in the molecule is obtained, it is seen that it is not a rational one. But if the ratio numbers of the similar oxides are combined, — that is, the number from the A1203 with that from the Fe203, and that from the FeO with those from the MnO, MgO and CaO, — it will be found that the relationship of the different groups of radicals can be expressed as Si02 : A1203 + Fe203 : FeO + MnO + MgO + CaO =3:1:3. From this it is seen that some of the possible A1203 has been replaced by isomorphous Fe203, and that a part of the FeO has been replaced by the isomorphous oxides of MnO, MgO and CaO. The formula for this garnet might be written, therefore, as 3R"0.lR2'"03.3Si02 or R3/,R*/,'(Si04)*, in which R" Fe, Mn, Mg and Ca, and It'" A1 and Fe.

Isomorphous Groups. A series of compounds which have analogous chemical compositions and closely similar crystal forms are said to make an isomorphous group. The artificial compounds known as the alums form a striking example. They are double salts of sulphuric acid, similar to the following, which is known as potash alum. They may vary in their composi tion by the substitution of Na, Li, NH4, etc., for the potassium and of Fe'" and Cr for the aluminum. All these compounds have, therefore, different but analogous compositions, and it is found also that they all crystallize in the Isometric System with an octahedral habit. Further, if a crystal of one alum is suspended in a saturated solution of another member of the series, the crystal will continue to grow, from this it is proved that, the molecules of the different

for each other in any proportion. Therefore this series of com pounds is said to be an Isomorphous Group.

Many such groups are to be found in minerals, and attention is called to them in various places in Section IV. Reference might be made to one of the most prominent of these in the case of the Calcite Group (see page 217). This is a series of minerals all of which are carbonates of similar bivalent metals, and therefore they can be said to have analogous chemical compositions. Further,

Dimorphism, Trimorphism, Etc.

they all crystallize in the same crystal system and class, and have closely agreeing angles between similar crystal faces. Conse quently they conform to the second requirement for an Isomorphous Group, namely, that the minerals of it should show similar crystal forms.

Dimorphism, Trimorphism, Etc.

A number of cases are well known among minerals in which two or three different species have the same chemical composition but distinctly different physical properties. When one compound appears in two different forms, it is said to be dimorphous: when in three different forms, trimorphous. Carbon in the forms of graphite and diamond, calcium carbonate as calcite and aragonite, iron sulphide as pyrite~ancl hinrcnsitp, familiar examples" of dimorphism. The two minerals in each case differ from each other in such physical properties as crystallization, hardness, specific gravity, color, reactions with acids, etc. Titanium g-ndr, rp;r> r trimorphous, since it occurs in the three distinct minerals, rutile, octahedrite and brookite. These instances furnish proof oT the statement that the physical characters of a mineral depend not only upon its chemical composition but upon its crystalline struc ture as well.

Solid Solution in Minerals. In certain minerals small variations in composition occur that cannot be accounted for by the presence of impurities or by the isomorphous replacement of one element or radical by another similar element or radical. These ext raordinary cases have been explained by the assumption that the mineral on crystallizing has formed a solid homogeneous solution with a small amount of foreign material. The relationship be tween the true mineral and the foreign matter can be compared to that between a dissolved salt and its solvent. Examples of solid solution in minerals are furnished by nephelite, NaAlSi04, the analyses of which always show a varying excess of silica, and by pyrrhotite, FeS, whose analyses show a small and varying excess of sulphur present.

Gel Minerals or Colloidal Minerals. There are a number of mineral substances analyses do not, yield n definite chemiml-

Manual Of Mineralogy

formula and further show no signs of a crystal structure. These are thought to he solid p1™*™* mnt.prin.1_n.nd have been

called "ac1-'wiv'*™1* - Minerals may exist in a crystalloid phase with a definite composition and molecular structure or, formed under different conditions, practically the same substance may occur as a mineral gel. The mineral pels are uadef-conditions of low pressure and temperature and are commonly sub stances of secondary origin formed during the process of weathering of the materials of the earth's crust. They characteristically occur in mammillary, botryoidal, stalactitic and similar forms. The power of these minerals to adsorb other substances to a consider able extent accounts for their often wide variations in chemical composition. Limonite and opal are familiar examples of-vel minerals.

Instruments, Reagents and Methods of Testing

The Blowpipe and Its Use. Many of the chemical tests made on minerals are performed by aid of an instrument known as a blowpipe. The blowpipe consists essentially of a tapering tube ending in a small and symmetrical opening through which air can be forced in a thin stream at high pressure. This current of air, when directed into a luminous flame, converts it into a small and very hot flame, by means of which many important tests can be made.

Fig. 200 represents a common type of blowpipe. The air is forced from the lungs into the mouthpiece, c, which fits into the upper end of the tube and issues from the small opening at the other end. The tip of the blowpipe, b, is placed just within a flat flame which is rich in carbon, such as is obtained from a candle or ordinary illuminating gas. A convenient method of producing a blowpipe flame is to use illuminating gas in a Bunsen burner, in which an inner tube, e (Fig. 201), has been placed so as to shut off the supply of air at the base of the burner and thus convert the flame into a luminous one. The upper end of this tube is flattened and cut at an angle, as is shown in Fig. 201. The gas flame is ordinarily adjusted so that it measures about 1 inch in height and j inch in breadth. The blowpipe is introduced into this flame as

Instruments, Reagents, Etc.

shown in Fig. 202. The resulting blowpipe flame should be nonluminous, narrow, sharp-pointed and clean-cut. If illuminating gas is not available, a candle with a flat wick or even an ordinary

Fig. 200

Fig. 201.

Fig. 202.

candle can be used. The latter require, however, more skill in manipulation.

The Art of Blowpiping. It usually requires some practice before one can produce a steady and continuous blowpipe flame.

Manual Of Mineralogy

Many tests can be made by means of a flame produced by exhaust ing the supply of air in the lungs simply once. But frequently an operation takes a longer time than this would give, and the inter ruption necessary in order to fill the lungs afresh would materially interfere with the success of the experiment. Consequently it often becomes important to be able to maintain a steady stream of air from the blowpipe for a considerable time. This is accom plished by distending the cheeks so as to form a reservoir of air in the mouth. When the supply of air in the lungs is exhausted, the passage from the mouth into the throat is closed by lifting the root of the tongue and while a new supply is being obtained by breathing in through the nose a steady stream of air is also being forced out of the reservoir in the mouth. In this way a constant flame may be obtained. It requires, however, considerable practice to do this skillfully.

The Character of the Blowpipe Flame. Fig. 202 represents a typical blowpipe flame. The inner cone, c, which is light blue in color and the most distinct part of the flame, is composed of un burned gas mixed with air from the blowpipe. There is no com bustion taking place in this part of the flame. Around this cone is a narrow pale- violet cone, b, which is almost invisible and in which the combustion does take place. Any gas that is used for the production of the flame will consist of some combination of carbon and hydrogen. These elements when the gas is burned are con verted into their respective oxides. The hydrogen burns directly to water vapor, H20. The carbon burns first to its lower oxide, CO, known as carbon monoxide. Later this oxide will be changed by the addition of another atom of oxygen to the higher oxide, C02, carbon dioxide. The final products of the combustion will, therefore, be the gases H20 and C02. In cone b, where combustion is taking place, there will necessarily be considerable amounts of the lower oxide of carbon, CO. Surrounding cone b there will be an invisible cone, a, consisting of the final products of combustion, C02 and H20.

Fusion by Means of Blowpipe Flame. A good blowpipe flame may reach a temperature as high as 2000° C. When skill fully handled small pieces of fine platinum wire may be melted in it.

Instruments, Reagents, Etc.

The determination of the degree of fusibility of a mineral is an important aid to its identification. In order to make the test, a small and if possible a sharply pointed fragment of the mineral should be inserted into the blowpipe flame just beyond the tip of the inner cone, where the combustion is most rapid and the tem perature the highest. The fragment should be held as illustrated in Fig. 203, so that it projects beyond the end of the forceps by which it is held in such a manner that the entire heat of the flame can be concentrated upon it. If it melts and rounds over, losing its sharp outline, it is said to be fusible in the blowpipe flame.

Fig. 203.

Minerals can therefore be divided into two classes, as to whether they are fusible or infusible in this flame. The minerals which are fusible can be further classified according to the degree of ease with which they fuse. To assist in this classification, a series of six minerals which show different degrees of fusibility has been chosen as a scale to which all fusible minerals may be approximately referred. For instance, when a mineral is said to have a fusibility of 3, it means that it will fuse with the same degree of ease as the mineral which is listed as 3 in the scale. In making such com parative tests, it is necessary to use fragments of the same size and to have the conditions of the experiments uniform. The minerals of the scale of fusibility are as follows:

1. Stibnile. Very easily fusible. A small splinter will readily melt in a candle flame.

Manual Of Mineralogy

2. Chalcopyrite. Easily fusible. A small fragment will fuse in the Bunsen burner flame.

3. Almandine Garnet. Infusible in the Bunsen burner flame but fuses easily in the blowpipe flame.

4. Actinolite. A sharp-pointed splinter fuses without much difficulty in the blowpipe flame.

5. Orthoclase. The edges of a fragment are rounded at the high est heat of the blowpipe flame.

6. Enstatite. Practically infusible in blowpipe flame, only the fine ends of sharp-pointed fragments being rounded.

Reducing and Oxidizing Flames. Reduction consists essen tially in taking oxygen away from a chemical compound, and oxidation consists in adding oxygen to it. These two opposite chemical reactions can be accomplished by means of a blowpipe flame. Cone b, Fig. 202, as explained above, contains CO, or car bon monoxide. This is what is known as a reducing agent, since, because of its strong tendency to take up oxygen in order to be come C02, or carbon dioxide, it will, if possible, take oxygen away from another substance in contact with it. For instance, if a small fragment of the ferric oxide of iron, hematite, Fe203, is held in this part of the blowpipe flame, it will be reduced by the removal of one atom of oxygen to the ferrous oxide, FeO, according to the following equation:

Fe203 + CO 2FeO + C02.

This change can be proved by noting that the ferric oxide is red in color and nonmagnetic, while the ferrous oxide is black and strongly magnetic. This cone b is therefore known as the reducing part of the blowpipe flame, and when it is wished to perform a reduction test the mineral fragment is placed at r, as shown in Fig. 202.

On the other hand, if oxidation is to be accomplished, the min eral must be placed entirely outside of the flame, where the oxygen of the air can have free access to it, but where it can still get in large degree the heat of the flame. Under these conditions, if the reaction is possible, oxygen will be added to the mineral and the

Instruments, Reagents, Etc.

substance will be oxidized. The oxidizing part of the blowpipe flame is at o (Fig. 202). Pyrite, FeS2, for instance, if placed in the oxidizing flame, would be converted into ferric oxide, Fe203, and sulphur dioxide, S02, according to the following equation :

2FeS2 + 110 Fe203 + 4S02.

The ferric oxide would form a dark-red residue, while the sulphur dioxide would come off as a pungent-smelling gas.

Use of Charcoal in Blowpiping. Small charcoal blocks, that should best be about 4 inches long, 1 inch wide and ) inch thick, are employed in a number of blowpipe tests. They are used as a support upon which various reactions are accomplished. For instance, metals like lead, silver, copper, etc., may be reduced from their minerals by means of the blowpipe flame, the experi-

Fig. 204. An Oxide Coating on Charcoal.

ment being performed upon charcoal. Characteristic oxide coat ings also may be obtained upon the surface of a charcoal block (see Fig. 204). The charcoal should be of a fine and uniform grain. It should not be so soft as to readily soil the fingers, nor should it be so hard as not to be easily cut and scraped by a knife. The following table gives a list of the elements which yield character istic oxide coatings when their minerals are heated in the oxidizing flame on charcoal. In some cases more characteristic coatings are obtained when the assay has had some chemical reagent added to it. The most important reagent is either hydriodic acid or the so-called bismuth flux, which consists of a mixture of potassium iodide and sulphur. When these reagents are used colored iodide coatings may result.

Manual Of Mineralogy

Composition of coating.

Color and character of coating on charcoal.

Remarks.

Arsenious Oxide. AS2O3.

White and volatile, depositing at some distance from the mineral.

Usually accompanied by garlic odor.

Antimony Oxides.

Sb203, Sb204.

White and volatile, depositing close to the mineral.

Heavier than arsenic oxide.

Selenium Oxide.

Volatile white, tinged with red on outside; to gray near assay.

Accompanied by . a peculiar odor. Coat ing touched with R. F. gives blue flame.

Tellurium Oxide. TeCb.

Dense white; volatile. On out side gray to brownish.

In R. F. coating gives bluish green flame color.

Zinc Oxide.

ZnO.

Yellow when hot, white when cold. Nonvolatile in the oxidizing flame. Deposits very close to mineral.

If coating is moistened with cobalt nitrate and heated intensely, it turns green.

Tin Oxide.

Faint yellow when hot, white when cold. Nonvolatile in the ox idizing flame.

Molybdenum Oxide. M0O3.

Pale yellow when hot, white when cold. Sometimes crystalline.

Volatile in the oxidizing flame.

If the coating is touched for a mo ment by a reducing flame, it becomes dark blue.

Lead Oxide.

PbO.

Yellow near the mineral and white farther away.

Coating at times is composed of white sulphite and sul phate of lead in ad dition to the oxide.

Lead Iodide.

PbR.

Chrome-yellow.

Volatile.

Bismuth Oxide. Bi203.

Yellow near the mineral and white farther away.

To be told from the lead-oxide coating by iodine tests (see p. 106).

Bismuth Iodide.

Bil3.

Bright red with yellow ring near assay.

Use of Plaster of Paris Tablets. In some cases it is preferable

to collect sublimates on the surface of a Plaster of Paris tablet rather than on charcoal. Such tablets can be easily made by spreading a thin layer of the wet plaster upon a glass plate, the surface of which has been oiled. While the plaster is still moist it should be cut into rectangular strips measuring about one and onehalf by four inches. After the plaster has hardened these can be

Instruments, Reagents, Etc. 95

broken out into the desired tablets. The material to be tested is placed in a small depression made near one end of the tablet and then heated before the blowpipe exactly as in the case with char coal. The iodide coatings are especially marked on the plaster tablet. The important tests are summarized in the table below.

Composition of coating.

Color and character of coating on plaster tablet.

Remarks.

Selenium Oxide. SeO*.

Red to crimson.

Volatile giving reddish fumes and char acteristic odor.

Tellurium Oxide. TeO a.

Dark brown.

Volatile.

Cadmium Oxide. CdO.

Greenish yellow with brown both tow'ard assay and at distance.

Nonvolatile.

Lead Iodide.

.

Chrome-yellow.

Bismuth Iodide.

Bii*

Chocolate-brown with underlying red.

Subjected to ammonia fumes coating be comes first orangeyellow then red.

Molybdenum Iodide. M0I4.

Deep ultramarine-blue.

Antimony Iodide. Sbl,.

Orange to red.

Disappears when sub jected to ammonia fumes.

Open Tube Test. Glass tubing of hard glass is used in making what are known as open tube tests. The tubing should be cut into approximately 8-inch lengths and have an internal diameter of inch- An open tube is used ordinarily for making oxidation tests. A small amount of the mineral to be tested is commonly powdered and placed in the tube at a point about one-third of its length from one end. A narrow strip of paper folded into a shal low trough will serve as a boat to introduce the powder into the tube. The tube is then inclined at as sharp an angle as possible, with the mineral lying nearer the lower end. The tube is then held over a Bunsen burner flame in such a way that the flame plays on the upper part of the tube. This serves to convert the inclined tube into a chimney, up which a current of air flows. After a moment the tube is shifted so that the flame heats it at a point

Manual Of Mineralogy

just above the mineral, or in some cases the flame may be directly beneath the mineral. The mineral is being heated under these conditions in a steady current of air, and it will be oxidized if such a reaction is possible. Various oxides may come off as gases and either escape at the end of the tube or be condensed as sublimates upon its walls. The following table gives a list of those elements which yield characteristic reactions when heated in open tubes:

Element Description of Test

Sulphur. Sulphur dioxide, S02, comes out of upper end of tube as a gas with a pungent and irritating odor. If a moistened strip of blue litmus paper is placed at the upper end of the tube, it becomes red, due to the acid reaction caused by the sulphurous acid.

Arsenic. Arsenious oxide, As203, condenses at a considerable distance above the heated portion as a volatile coating of small colorless octahedral crystals.

Antimony. Antimonious oxide, Sb203, deposits as a volatile white ring closer to the heated portion of the tube than the arsenious oxide. Antimony sulphides yield also a dense nonvolatile white sublimate of antimonate of antimony, Sb204, which collects along the bottom of the tube.

Molybdenum. Molybdenum trioxide, M0O3, collects near the heated portion as a network of pale yellow to white crystals.

Mercury. Collects in minute gray globules which can be rubbed together.

Note. Other reactions may be obtained from some of the above elements if the mineral is heated too rapidly -or without the es tablishment of a strong current of air flowing through the tube Closed Tube Test. Frequently a small glass tube which has been closed at one end is useful in testing minerals. The tube is made out of soft glass and should have a length of about 31 inches and an internal diameter from to rs of an inch. Two closed

Instruments, Reagents, Etc.

tubes can easily be made by fusing the center of a piece of tubing 7 inches in length and pulling it apart. The closed tube test is used to determine what takes place when a mineral is subjected to heat practically out of contact with the air. Ordinarily there is no chemical reaction involved. In general, in the closed tube the mineral will break down into simpler parts if that is possible, but otherwise nothing will take place except possibly a fusion of the mineral. The following table gives a list and brief description of the important closed tube tests :

Substance Description of Test

Water, H20. All minerals containing water of crystallization or the hydroxyl radical will give on moderate heating a deposit of drops of water on the cold upper walls of the tube.

Sulphur, S. All sulphides which contain an excess of sulphur will give a sublimate of sulphur, which is red when hot and yellow when cold.

Arsenic, As. Native arsenic and some arsenides will give a de posit of metallic arsenic. This consists of two rings, one being composed of a black and amorphous material, the other lying nearer the bottom of the tube, of a silver-gray and crystalline material.

Oxysulphide of antimony, Sb2S20. Sulphide of antimony and some sulphantimonites give this sublimate in the form of a slight coating which deposits close to the bottom of the tube. It is black when hot and red when cold. It is accompanied by a faint deposit of sulphur further up the tube.

Sulphide of mercury, HgS. A black amorphous sublimate which forms when cinnabar is heated.

Mercury, Hg. Gray globules of metallic mercury are obtained when native mercury or amalgams are heated or when the sulphide is mixed with diy sodium carbonate and heated.

Manual Of Mineralogy

Flame Test. Certain elements may be volatilized when min erals containing them are heated intensely before the blowpipe and so impart characteristic colors to the flame. The flame color to be obtained from a mineral will often serve as an important means of its identification. A flame test may be made by heating a small fragment of the mineral held in the forceps, but a more decisive test is usually obtained when the fine powder of the mineral is introduced into the Bunsen burner flame on a piece of fine platinum wire. The following table gives a list of the important elements which yield flame colors. It is to be noted that a mineral may contain one of these elements, but because of the nonvolatile character of the chemical combination will fail to give a flame color.

Element Color of Flame Remarks

Strontium.

Crimson.

Strontium minerals which give the flame color also give alkaline residues after being heated.

Lithium.

Crimson.

Lithium minerals which give the flame color do not give alkaline residues after being heated.

Calcium.

Orange.

In the majority of cases a dis tinct calcium flame will be ob tained only after the mineral has been moistened with HC1.

Sodium.

Intense yellow.

A very delicate reaction. The flame should be very strong and persistent to indicate the pres ence of sodium in the mineral as an essential constituent.

Barium.

Yellow green.

Minerals which give the barium flame also give alkaline residues after ignition.

Molybdenum.

Yellow green.

Obtained from the oxide or sul phide of molybdenum.

Instruments, Reagents, Etc.

Boron.

Yellow green.

Minerals giving a boron flame rarely give alkaline residues after ignition.

Emerald-green.

Obtained from the oxide of

Copper.

Azure-blue.

copper.

Obtained from the chloride of

copper.

Zinc.

Bluish green.

Appears usually as bright streaks and threads in the flame.

Lead.

Pale azure-blue.

Tinged with green in the outer parts.

Color Reactions with the Fluxes. Some elements, when dissolved in certain fluxes, give a characteristic color to the fused mass. The fluxes that are most commonly used are borax, NaJOj.lOlEO, sodium carbonate, Na2C03, and salt of phosphorus, HNaNH4P04.4H20. The Q

operation is best performed by first fusing the flux on a small loop of platinum wire into the form of a lens-shaped bead. The loop on the wire should best have the shape and size shown in Fig. 205. After the flux has been fused into a bead on the wire, a small amount of the Wire for Bead

powdered mineral is introduced into it and is Tests,

dissolved by further heating. The color of the resulting bead may depend upon whether it was heated in the oxidizing or reducing flame and whether the bead is hot or cold. The following table gives a list of the important bead tests:

Manual Of Mineralogy

Table of Color Reactions with the Fluxes.

Oxides of

Borax Bead.

Phosphorus Salt Bead.

Oxidizing flame.

Reducing

flame.

Oxidizing flame.

Reducing

flame.

Chromium.

Hot.

Yellow.

Green.

Dirty green.

Dirty green.

Cold.

Yellowish green.

Green.

Fine green.

Fine green.

Vanadium.

Hot.

Yellow.

Dirty green.

Yellow.

Dirty green.

Cold.

Yellowish green almost color less.

Fine green.

Yellow.

Fine green.

Uranium.

Hot.

Deep yellow to orange-red.

Pale green.

Yellow.

Pale dirty green.

Cold.

Yellow.

Pale green to nearly colorless.

Pale greenish yellow.

Fine green.

Iron.

Hot.

Deep yellow to orange-red.

Bottle-green.

Deep yellow to brownish red.

Red-yellow to yellowgreen.

Cold.

Yellow.

Pale bottlegreen.

Yellow to al most colorless.

Almost color less.

Copper.

Hot.

Green.

Colorless to green.

Green.

Brownish

green.

Cold.

Blue.

Opaque red with much oxide.

Blue.

Opaque red.

Cobalt.

Hot.

Blue.

Blue.

Blue.

Blue.

Cold.

Blue.

Blue.

Blue.

Blue.

Nickel.

Hot.

Violet.

Opaque gray.

Reddish to browTiish red.

Reddish to brownish red.

Cold.

Reddish brown.

Opaque gray.

Yellow to red dish yellow.

Yellow to red dish yellow.

Manganese.

Hot.

Violet.

Colorless.

Grayish violet.

Colorless.

Cold.

Reddish violet.

Colorless.

Violet.

Colorless.

Sodium carbonate with oxide of manganese gives when heated in the oxidizing flame an opaque bead, green when hot, bluish green

Reagents

when cold. When heated in the reducing flame the bead is color less.

Dry Reagents

The following paragraphs give a brief description of the more important dry reagents used in testing minerals :

Sodium Carbonate, Na2C03, is a white salt that is used chiefly as a flux to decompose minerals by fusion on charcoal and more rarely as a flux in a bead test.

Borax, Na2B.iO7-10lI>(), is a white salt that is used chiefly in making bead tests and more rarely as a flux on charcoal.

Microcosmic Salt or Salt of Phosphorus, HNaNH4P04.4H20, is a white salt used in making bead tests.

Acid Potassium Sulphate, HKS04, is a white salt that is used in making a test for fluorine (see page 109).

Acid Potassium Sulphate and Fluorite Mixture is a mixture of three parts of the former and one part of the latter. It is used in making a test for boron (see page 107).

Potassium Iodide and Sulphur Mixture. A mixture of equal parts of these two materials is used in making a test for bismuth (see page 106).

Tin and Zinc are used in granulated form to make certain re duction tests in hydrochloric acid solutions.

Test Papers. Blue litmus paper is a test paper which changes in color from blue to red when exposed to the action of an acid. It is most commonly used in the open tube test for sulphur (see page 1 19) . Yellow turmeric paper is a test paper that turns brown when exposed to the action of an alkali. It is most commonly used in making a test for the presence of an alkali or alkaline earth in a mineral (see under sodium, page 118, calcium, page 107, etc.). Red litmus paper can be substituted for the yellow turmeric. It turns blue when exposed to the action of an alkali.

Wet Reagents

The following paragraphs give a brief description of the more important wet reagents used in testing minerals:

Hydrochloric Acid, Muriatic Acid, HC1, is an acid which is commonly used for the solution of minerals, etc. It is a non-

Manual Of Mineralogy

oxidizing acid. The ordinary laboratory acid is diluted with three parts of water.

Nitric Acid, HN03, is a strong solvent and oxidizing agent. It is commonly used in its concentrated form.

Sulphuric Acid, H2S04, is less commonly used than the others as a solvent. It may be used in its concentrated form, but usually is diluted with four parts of water. When water is added to the acid a large amount of heat is generated. Water should never be added to the hot acid. The acid boils at 337° C.

Ammonium Hydroxide, NH4OH, is a strong alkali used chiefly to neutralize acid solutions and as a precipitant for alu minum and ferric hydroxides (see pages 104 and 111). For labo ratory use it is commonly diluted with three parts of water.

Ammonium Carbonate, and Ammonium Oxa late, are chiefly used in the form of aqueous solutions to precipitate the alkaline earths, calcium, strontium and barium, from their solutions (see page 107).

Hydrogen Sodium Phosphate, HNa2P04, is used in the form of an aqueous solution to test for the presence of magnesium (see page 112); Barium Hydroxide, in testing for carbon dioxide (see page 108); Barium Chloride, BaCl2, for sulphuric acid (see page 120); Ammonium Molybdate, for phosphoric acid (see page 115); Silver Nitrate, AgN03, for chlorine (see page 108).

Potassium Ferrocyanide, KJCNVStBO, and Potassium Ferricyanide, are used in dilute solutions to test for ferric and ferrous iron respectively (see page 111). Ammoni um Sulphocyanate, NH4CNS, is also used to test for ferric iron. Cobalt Nitrate, is used in the form of a dilute solution in blowpipe tests for aluminum and zinc (see pages 104 and 123).

Tests for the Elements

On the following pages will be given brief descriptions of the more important blowpipe and chemical tests for the elements as they occur in minerals. In order to facilitate reference to this section, the different elements will be treated in alphabetical order.

Tests For The Elements

Under each element the tests will be given in the approximate order of their importance. For a fuller discussion of this part of the subject reference must necessarily be made to the textbooks that treat of it alone. Below is a list of the elements whose tests are discussed, with their chemical symbols, valence and atomic weights.

Element.

bol.

Valence.

Atomic

Weight.

A1

Sb

Ba

Be

Bi

B

Ca

Cr

Co

Columbium, see Niobium.

Cu

F

Glucinum, see Beryllium. Gold .

Au

H

Fe

Pb

Mg

Mn

Manganese .

Bivalent, trivalent and tetra valent.

Hg

Mo

Ni

Nb

P

Pt

K

Si

Ag

Na

Sr

s

Ta

Te

Tin

Sn

Ti

W

u

Tetra valent and sexi valent .

Zn

Manual Of Mineralogy

Aluminum

1. Precipitation by Ammonium Hydroxide. Aluminum is

precipitated in the form of aluminum hydroxide, when an excess of ammonium hydroxide is added to an acid solution. The precipitate is flocculent in form and colorless or white. It is precipitated under the same conditions as ferric hydroxide (see page 111), and since the latter has a dark color a small amount of aluminum hydroxide might be overlooked in a mixture of the two. To make a further test under these conditions, filter off the precipitate and treat it with a hot solution of sodium hydroxide, which will dissolve any aluminum hydroxide present but will not affect the ferric hydroxide. Filter, and to the filtrate add hydrochloric acid in slight excess, and then make alkaline with ammonium hydroxide again. This will precipitate any aluminum that may be present as pure aluminum hydroxide.

2. Blowpipe Test with Cobalt Nitrate. Light colored and infusible aluminum minerals when moistened with a drop of cobalt nitrate and heated intensely before the blowpipe assume a dark blue color. Zinc silicates will also yield a blue color under similar conditions.

Antimony

1. Oxide Coating on Charcoal. When an antimony mineral is heated in the oxidizing flame on charcoal, a heavy white coating of antimony oxide settles on the charcoal at a short distance from the mineral. The coating is readily volatile when heated.

2. Open Tube Test. When metallic antimony or a compound of antimony with sulphur is heated in the open tube, a white powdery sublimate of antimony oxide, Sb203, forms in a ring on the inner wall of the tube, a short distance above the mineral. It is a volatile coating. If the mineral contains sulphur, as is usually the case, a second coating will form as a white powder along the bot tom of the tube. It is another oxide of antimony, Sb204. It is nonvolatile and is usually more conspicuous than the first.

3. Sublimate on Plaster Tablet. Mixed with a mixture of potassium iodide and sulphur yields in the oxidizing flame an orange to red sublimate of Sbl3.

Arsenic

Arsenic

The test to be used for arsenic depends upon whether the min eral contains oxygen. In the majority of cases an arsenic com pound does not contain oxygen, and then tests 1, 2, 3 and 4 will serve. If, on the other hand, the mineral is an oxygen compound, test 5 must be used.

1. Oxide Coating on Charcoal. When an arsenic mineral is heated in the oxidizing flame on charcoal, a white coating of arsenious oxide, As203, is deposited on the charcoal at some distance from the mineral. The coating is very volatile. Its formation is usually accompanied by a characteristic odor of garlic.

2. Sublimate on Plaster Tablet. When mixed with a mix ture of potassium iodide and sulphur arsenic minerals yield in the oxidizing flame an orange-yellow coating of Asl3.

3. Open Tube Test. When an arsenic mineral is carefully heated in the open tube a colorless or white crystalline sublimate of arsenious oxide, As203, forms in a ring on the inner wall of the tube at a considerable distance above the mineral. It is very volatile. When examined with a lens the coating will usually show well-defined octahedral crystals. If the mineral is heated too rapidly, metallic arsenic may sublime instead of the oxide (see the next test).

4. Closed Tube Test. Many arsenic minerals when heated in a closed tube yield a sublimate of metallic arsenic, known as the arsenic mirror. This sublimate shows an amorphous black band above and a silver-gray crystalline band below. If the bottom of the tube be broken off and the metallic arsenic volatilized by heat, the characteristic garlic odor will be obtained.

5. Closed Tube Test for an Arsenate. When arsenic occurs in a mineral in the form of an arsenate, i.e., an oxidized com pound, none of the above tests will serve. In this case place the mineral in a closed tube with a splinter of charcoal and then heat. The charcoal will act as a reducing agent and set metallic arsenic free, which will condense on the wall of the tube as an arsenical mirror similar to that described under test 4.

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Barium

1. Flame Test. Barium minerals, with the exception of barium silicates, when heated intensely give a yellowish green flame color.

2. Precipitation as Barium Sulphate. Barium is precipi tated as barium sulphate, BaSCh, from an acid solution by the addition of dilute sulphuric acid. The precipitate is white and finely divided and being very insoluble will form in a quite dilute solution (distinction from calcium and strontium).

3. Alkaline Reaction. Barium is an alkaline earth metal. When a mineral contains barium in combination with a volatile acid, it will give, after ignition, a residue which will react alkaline on a piece. of moistened turmeric paper.

Beryllium or Glucinum

Beryllium is a rare element which has no simple blowpipe or chemical test.

Bismuth

1. Charcoal Tests. When heated with sodium carbonate on charcoal in the reducing flame, a bismuth mineral will yield a metallic globule and an oxide coating. The metal is easily fusible, lead-gray when hot, but becomes covered with an oxide coating on cooling. It is only imperfectly malleable, for when hammered out it flattens at first but later breaks into small grains. The oxide coating, Bi,0:, is white with a yellow ring next the mineral. These bismuth reactions are quite similar to those for lead (see page 112), consequently the following modification is useful. If the bismuth mineral is fused on charcoal with a mixture of potassium iodide, KI, and sulphur (see page 101), a characteristic and distinctive coating is obtained. This sublimate is yellow next to the mineral and brilliant red on the outside. Under similar conditions with lead a solid yellow coating would be obtained.

2. Sublimate on Plaster Tablet. When mixed with a mix ture of potassium iodide and sulphur and heated a bismuth mineral will give a sublimate that is chocolate-brown with underlying red in

Calcium

color. Subjected to ammonia fumes the coating becomes first orange-yellow, then red.

Boron

1. Flame Test. Some boron minerals give a yellow-green flame when heated alone. Most boron minerals, however, will only yield the flame color when their powder is mixed with acid potassium sulphate and fluorite mixture (see page 101) and then introduced on a platinum wire into a Bunsen burner flame. As the mixture fuses, a momentary but distinct green flame is obtained.

Calcium

1. Flame Test. When calcium occurs in a mineral in such a state that it can be volatilized by heat, it will yield a characteristic orange flame color. Frequently the mineral has to be moistened by hydrochloric acid before heating. The flame should not be confused with the crimson and more persistent flame of strontium or lithium.

2. Alkaline Reaction. Calcium is an alkali-earth metal. When a mineral contains calcium in a combination with a volatile acid, it will give, after ignition, a residue which will react alkaline on a piece of moistened turmeric paper.

3. Precipitation as Calcium Oxalate or Carbonate. Cal cium is readily and completely precipitated from alkaline solu tions as calcium oxalate, CaC204, or calcium carbonate, CaC03, by the addition of ammonium oxalate, or ammonium carbonate, Both precipitates are white and finely divided.

4. Precipitation as Calcium Sulphate. Calcium is precipi tated from a concentrated hydrochloric acid solution as calcium sulphate on the addition of a little dilute sulphuric acid. The precipitate is quite readily soluble in water and therefore will not form in a dilute solution (distinction from barium and strontium).

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Carbon

Carbon exists in minerals chiefly in the form of carbonic acid in the carbonates.

1. Test for Carbon Dioxide with an Acid. All carbonates when treated with a strong acid (best hydrochloric) dissolve with a vigorous effervescence of carbon dioxide gas. In some cases (for example, dolomite, the acid needs to be heated to start the reaction, and in others (for example, cerussite, PbC03) a dilute acid is necessary. Carbon dioxide gas is colorless and odor less. It will not support combustion, as is shown when a lighted match is placed in a test tube that contains it. The gas is heavier than air and can be poured from the test tube in which it has been generated into another in which some barium hydroxide solution has been placed. When the contents of the latter tube are shaken together, the carbon dioxide reacts with the barium hydroxide to form a white precipitate of barium carbonate, BaC03.

Chlorine

1. Precipitation as Silver Chloride. Chlorine is precipi tated from a dilute nitric acid solution as silver chloride, AgCl, by the addition of a small amount of silver nitrate, AgN03. The test is very delicate, traces of chlorine being shown by a milky appear ance of the solution. When in any quantity the precipitate is curdy in form. It is white on precipitation but darkens on exposure to light. It is soluble in ammonium hydroxide. The rare elements, bromine and iodine, would give similar reactions.

Chromium

1. Bead Tests. Chromium is usually tested for by the color it gives to the fluxes (see page 100). The salt of phosphorus bead when fused in the oxidizing flame yields a fine green color. This is the most characteristic chromium bead.

Cobalt

1. Bead Tests. A cobalt mineral when fused in either a borax or salt of phosphorus bead yields a distinctive dark blue color. The test is very delicate.

Fluorine

Columbium, see Niobium Copper

1. Flame Tests. An oxidized compound of copper when introduced into the flame gives it a vivid green flame color due to the copper oxide volatilized. When the mineral is moistened with hydrochloric acid and then heated, the flame color is an intense blue. If the mineral is a sulphide, it must be roasted in the oxidiz ing flame before moistening with hydrochloric acid.

2. Blue Solution with Ammonium Hydroxide. If an acid solution containing copper is made alkaline with ammonium hydroxide, it will assume a deep blue color.

3. Reduction to Metal on Charcoal. When a small amount of a copper mineral is mixed with a flux (best equal parts of sodium carbonate and borax), placed on charcoal and heated intensely in the reducing flame, metallic globules of copper will be formed. They are difficultly fusible, bright when hot, but become coated with an oxide coating on cooling. They are malleable and show the characteristic copper color. Sulphides of copper must first be roasted in the oxidizing flame in order to remove the sulphur before mixing with the flux.

Fluorine

1. Etching Tests. The ordinary test for fluorine consists in converting it into hydrofluoric acid and observing the latter's etching effect upon glass. A watch glass or other piece of glass may be covered with paraffin and then the coating removed in spots. Upon this is placed the powdered mineral with a few drops of concentrated sulphuric acid. The action of the acid upon the fluoride will serve to liberate hydrofluoric acid, which will in turn etch the glass where it has been exposed. The action should be allowed to continue for some time, when on cleaning the glass the etched spots will be visible.

A modification of the above test can be made in a closed tube. Take a closed tube of about inch diameter and made preferably of hard glass. Into this introduce a powdered mixture of the min eral, glass, and acid potassium sulphate, and then heat in the

Manual Of Mineralogy

Bunsen burner flame. When heated, acid potassium sulphate is converted into the normal potassium sulphate with the liberation of sulphuric acid. The acid attacks the fluoride and sets free hydrofluoric acid. This in turn acts upon the glass present and etches it. The etching, however, is not readily apparent on ac count of the conditions of the experiment. As a secondary re action, however, there will be formed in the upper part of the tube a white sublimate of silicon dioxide. This sublimate is volatile because of the presence with it of small amounts of hydrofluosilicic acid. If the bottom of the tube is broken off and its interior gently washed with water, this acid will be dissolved and removed. If the tube is now dried again, the white coating will prove to be no longer volatile. This silicon dioxide coating is a proof of the action of hydrofluoric acid in the bottom of the tube and therefore of the presence of fluorine in the mineral. A similar test may be made by substituting sodium metaphosphate for acid potassium sulphate. The sodium phosphate may be prepared by fusing salt of phos phorus to a glass.

Glucinum, see Beryllium Gold

There is no simple blowpipe or chemical test for gold. Ordi narily its physical characteristics are sufficient to identify it. For a discussion of the occurrence and tests for gold see page 137.

Hydrogen

1. Closed Tube Test for Water. Hydrogen exists in minerals either as water of crystallization (for example, gypsum, CaS04- 2H20) or as the hydroxyl radical (for example, brucite, In either case its presence may be detected by heating a fragment of the mineral in a closed tube and observing the water which con denses upon the upper cold wall of the tube. Water of crystalli zation is driven off more readily than water of hydroxyl, but the test is easily obtained in either case.

Iron

Iron

1. Magnetic Test. Any mineral that contains a sufficient amount of iron to permit it to be classified as an iron mineral will readily become magnetic when heated in the reducing part of the blowpipe flame. A comparatively small fragment should be used and the test made with a magnet after it has cooled.

2. Precipitation with Ammonium Hydroxide. Ferric iron is readily and completely precipitated as ferric hydroxide, from an acid solution by adding an excess of ammonium hydroxide. It is a flocculent precipitate with a reddish brown color. If there is any doubt as to the state of oxidation of the iron in the original solution, a few drops of nitric acid should be added and the solution heated in order to make certain that the iron is ferric.

3. Cyanide Tests for Ferrous and Ferric Iron. Occasion ally it may be important to determine whether the iron in a mineral is ferrous or ferric in its valence. This can be done only when the mineral is soluble in a nonoxidizing acid like hydrochloric and when it is not a sulphide. If these conditions can be fulfilled, then divide the solution into two parts. To one add a few drops of a dilute solution of potassium /m'cyanide, and if the solution contains any ferrous iron a heavy dark blue precipitate will form. If, on the other hand, it contained only ferric iron, there would be no pre cipitate but only a darkening of the color of the solution. To the second portion of the solution add a few drops of a dilute solution of potassium /erocyanide, and if there is any ferric iron present a heavy dark blue precipitate similar to the one in the previous case null form. But if the solution contained only ferrous iron, a light blue precipitate would be formed. The characteristic dark blue precipitate must contain both valences of iron and will only form when a cyanide is added containing the opposite kind of iron to that already in the solution.

Ammonium or potassium sulphocyanate is also used in making the ferric test. A few drops of one of these reagents added to a ferric iron solution will give it a deep red color. All of these tests are extremely delicate and wall give good results if only a trace of iron is present. They should never be used to determine the pres-

Manual Of Mineralogy

ence of iron in a mineral but only to differentiate ferrous from ferric iron.

Lead

1. Charcoal Test. Any lead mineral when powdered and mixed with sodium carbonate will yield a metallic globule when the mixture is heated on charcoal in the reducing flame. The globule is bright lead color when hot, but becomes covered with a dull oxide coating on cooling. It is very malleable and can be hammered out into a thin sheet. A coating on the charcoal of lead oxide, PbO, will also form, which varies in color from yellow next to the fused mass to white at a distance. It will be best obtained by removing the lead globule to a fresh piece of charcoal and heating it in the oxidizing flame.

2. Iodide Tests. When lead minerals are mixed with a mixture of potassium iodide and sulphur and heated on either charcoal or plaster they yield a chrome-yellow coating.

3. Acid Tests. Lead minerals as a rule are only slowly at tacked by acids. Dilute nitric acid is the best solvent to use. If to a nitric acid solution a few drops of hydrochloric or sulphuric acid are added, white precipitates will form, which are respectively lead chloride, PbCl2, and lead sulphate, PbS04. The latter is quite insoluble.

Lithium

1. Flame Test. Lithium is a rare element which is to be dis tinguished by the persistent and strong crimson color which it gives to the flame. In the case of silicates it is better to mix the powdered mineral with powdered gypsum before testing for the flame color. The flame is very similar to that obtained from strontium.

Magnesium

1. Precipitation as Ammonium Magnesium Phosphate.

The only common test for magnesium is to precipitate it in the form of ammonium magnesium phosphate, NH4MgP04, by the

Mercury

addition of hydrogen sodium phosphate, HNa2P04, to a strongly ammoniacal solution. The precipitate usually forms somewhat slowly, is white in color, and frequently is granular in texture. In order to make a decisive test certain precautions are necessary. As the precipitation is made in an ammoniacal solution, any pre cipitates formed by an excess of ammonium hydroxide must be first filtered off. It may be necessary before adding the ammonium hydroxide to add a few drops of nitric acid so as to make certain that any iron in the solution is in the ferric state. Also, before making the final test, any elements, such as calcium, strontium and barium, that are precipitated in ammoniacal solution by means of ammonium oxalate, must be removed. In any case their presence must be tested for before adding the hydrogen sodium phosphate, because, if present, they would be precipitated by that reagent along with the magnesium.

Manganese

1. Bead Tests, a. Manganese gives to the sodium carbonate bead when heated in the oxidizing flame a characteristic bluish green color. The bead is opaque when cold.

b. With the borax bead, when heated in the oxidizing flame manganese gives a purple or amethystine color. The bead is transparent when cold.

Both tests are very delicate.

Mercury

1. Closed Tube Tests. The powdered mineral is thoroughly mixed with dry sodium carbonate and placed in a closed tube and then heated. The sodium carbonate will decompose the mineral and liberate metallic mercury, which will volatilize and condense in the upper part of the tube.

2. Precipitation on Copper. Boil the powdered mineral with hydrochloric acid, into which some powdered pyrolusite, Mn02, has been placed. The chlorine evolved by the action of the acid on the manganese dioxide will serve to dissolve the mercury mineral. If into this solution a clean strip of copper is placed (a

Manual Of Mineralogy

cent which has been cleaned with a little nitric acid will serve), it will become covered by a thin coating of metallic mercury.

The chief and only common mineral of mercury is cinnabar, HgS, and for its distinctive physical and chemical tests see page

Molybdenum

The tests for the rare element molybdenum depend upon whether it is in combination with sulphur or in an oxygen com pound. See under molybdenite, page 148, and under wulfenite, page 325, for descriptions of the various tests.

Nickel

1. Borax Bead Test. When dissolved in a borax bead in the oxidizing flame, nickel will give it a brownish color. If the bead is heated in the reducing flame for some time, it will become opaque because of the separation in it of metallic nickel. The brown color due to nickel is often masked by the deep blue color due to the presence of cobalt, which is frequently associated with nickel in its occurrence. In this case there is no simple test for nickel.

2. In Ammoniacal Solution. A comparatively strong acid solution of nickel will on the addition of an excess of ammonium hydroxide become light blue in color. The test should not be confused with the similar but stronger test for copper.

3. Precipitation of Nickel by Dimethylglyoxime. Dissolve the mineral in nitric acid and neutralize with ammonium hydroxide. Filter if necessary. Add a little of a solution of dimethylglyoxime and a scarlet crystalline precipitate forms.

Niobium

Niobium, or columbium, as it is sometimes called, is a rare acid element that is associated with tantalum in the niobates and tantalates.

1. Reduction Test with Tin. The best test for niobium is to fuse some of the powdered mineral with several parts of sodium carbonate. The resulting mass is dissolved in a few cubic centi-

Phosphorus

meters of dilute hydrochloric acid and then a few grains of metallic tin are added. The solution is boiled and the hydrogen set free by the action of the acid on the tin serves as a reducing agent. The result is to form a compound of niobium which is dark blue in color. This color does not readily change to brown on continued boiling, and disappears on addition of water. This distinguishes the niobium test from a similar one for tungsten (see page 122).

Oxygen

While oxygen is one of the most common elements in minerals, its presence is ordinarily determined indirectly by testing for the different oxygen acids. In the case of a few oxides in which there is an excess of oxygen, a direct test may be made.

1. Closed Tube Test. The powdered oxide is placed in a closed tube with a small splinter of charcoal resting just above it. The tube is heated and if free oxygen is evolved the charcoal will at first glow and then burn with a bright light. It is to be noted that only a few oxides which contain an excess of oxygen will give this test.

2. Evolution of Chlorine. Oxides that contain an excess of oxygen when dissolved in hydrochloric acid will produce chlorine gas.

Phosphorus

1. Precipitation with Ammonium Molybdate. Phosphorus exists in minerals in the form of phosphoric acid in the phosphates. It is best tested for by forming a dilute nitric acid solution of the mineral and adding a few cubic centimeters of this to an excess of ammonium molybdate solution. A canary-yellow precipitate of ammonium phosphomolybdate will be formed. The precipitate forms slowly at first and comes down best in a warm solution.

2. Flame Test. Many phosphates when heated before the blowpipe give a pale bluish green flame color. This may frequently be obtained better when the mineral has previously been moistened with a drop of concentrated sulphuric acid.

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Platinum

There are no simple blowpipe or chemical tests for platinum. The physical characteristics of the metal are usually sufficient for its identification (see page 142).

Potassium

1. Flame Test. Volatile potassium salts give a characteristic pale violet flame color. The potassium flame will, however, com monly be obscured by the stronger yellow flame of sodium. This difficulty can be overcome by filtering the flame through a piece of blue glass. The sodium flame, being a mono-chromatic light, can not pass tin ough the blue glass, while the violet flame of potassium will be visible.

When the potassium does not exist in the mineral in a volatile state, as in the case with potassium silicates, the powdered min eral must be first thoroughly mixed with gypsum (CaS04.2H20) and the mixture introduced into the Bunsen burner flame on a platinum wire. There will be a reaction between the two, and the potassium will be liberated in the form of a sulphate, which, being a volatile salt, will give the flame color. It will be momentary in duration and must be viewed through the blue glass.

Silicon

Silicon exists as the acid element in the large group of minerals known as the silicates. Some of these are readily soluble in acids, but the greater part are quite insoluble. The tests employed differ somewhat in the two cases.

1. Test for a Soluble Silicate. If the silicate is soluble, it should be powdered and dissolved in boiling hydrochloric acid. When this solution is evaporated a jellylike material will separate out just before dryness is reached. This silica jelly, as it is called, is a form of silicic acid and proves the presence of silicon in the mineral. On continued evaporation it will be dehydrated and converted into a sandy and insoluble substance having the com position of silicon dioxide, Si02.

Silicon

2. Test for an Insoluble Silicate. In the case of an insoluble silicate, the mineral must be decomposed by fusion with sodium carbonate before treating it with an acid. Make a mixture of one part of the powdered mineral to three parts of sodium carbonate and fuse thoroughly before the blowpipe on a loop of platinum wire. It is best to make two or three such beads. The fusion serves to decompose the silicate and to render the resulting mass w'holly soluble in acids. The beads are powdered and dissolved in boiling dilute nitric acid. The evaporation is conducted as explained in experiment 1 and a similar silica jelly is obtained.

Frequently it is desirable to make tests for the bases which are present in the silicate. In this case, after the formation of the jelly, continue the evaporation to complete dryness. This con verts the silicon into the insoluble oxide but leaves the bases in the form of various soluble salts. Treat the residue in the test tube with a little water and hydrochloric acid, warm and filter from the insoluble silica. Add an excess of ammonium hydroxide to the filtrate to precipitate any aluminum or ferric iron as their re spective hydroxides. Filter if necessary, and to the filtrate add a little ammonium oxalate to precipitate any calcium as calcium oxalate. Filter again, and to the filtrate add more ammonium hydroxide if necessary and then a little hydrogen sodium phosphate, which will precipitate any magnesium present as ammonium magnesium phosphate.

3. Decomposition of Silicates by Acids. Certain silicates, when their powder is treated with boiling hydrochloric acid, are decomposed, the bases going into solution and the silicon separating as the dioxide, Si02. In this case there would be no jelly formed when the solution is evaporated. The mineral powder in such cases disappears, but the solution never becomes perfectly clear owing to the silica, w'hich remains in suspension in the solution. It gives the solution a translucent appearance. The surest proof that the mineral has been decomposed is to filter the solution and test for various bases in the filtrate in a similar manner to that described under test 2.

4. Test with the Salt of Phosphorus Bead. When the powder of a silicate is heated in a salt of phosphorus bead, the

Manual Of Mineralogy

bases are dissolved, leaving the silica present as an insoluble trans lucent skeleton.

Silver

1. Reduction to the Metal on Charcoal. Silver can fre quently be reduced to a metallic globule from its compounds by heating the powdered mineral on charcoal with sodium carbonate. The resulting globule is bright both when hot and cold. It is malleable. No accompanying coating is formed on the charcoal. This test for silver is frequently complicated by the presence of lead, arsenic or antimony in the mineral. Usually the mineral should be carefully roasted on charcoal in the oxidizing flame before attempting the reduction in order to remove the last two; otherwise a brittle globule will result. In many cases the only satisfactory test for silver is the fire assay.

2. Precipitation as Silver Chloride. When a silver mineral is dissolved in nitric acid and to the solution a few drops of hydro chloric acid is added, a white curdy precipitate of silver chloride, AgCl, is formed. The test is quite delicate, and if there is only a trace of silver in the solution its presence will be indicated by a milky-blue coloration. The precipitate is white at first but darkens on exposure to light. It is soluble in ammonium hydroxide. Frequently when a silver mineral is treated with nitric acid a precipitate will result at once. This may be metantimonic acid, lead sulphate, etc., and should be filtered off before making the silver test.

Sodium

1. Flame Test. Sodium compounds when heated give a strong and persistent yellow flame. The test is very delicate and must be used with care, for only a trace of sodium may yield a distinct flame. If the mineral contains sodium in any notable amount, it should give an intense and continuous flame color.

2. Alkaline Reaction. A compound of sodium with a volatile acid yields after ignition a residue that reacts alkaline on a mois tened test paper.

Sulphur

Strontium

1. Flame Color. Strontium compounds give a very strong and persistent crimson flame. The only other flame which is similar is that obtained from lithium. Strontium can be positively determined from lithium by the following tests.

2. Alkaline Reaction. When a mineral contains strontium m combination with a volatile acid, it will give, after ignition, a residue which will react alkaline on a piece of moistened turmeric paper.

3. Precipitation as Strontium Sulphate. Strontium is pre cipitated from a mediumly dilute solution as strontium sulphate, SrS04, on the addition of a little dilute sulphuric acid. The precipitate is somewhat soluble and will not form in very dilute solutions (distinction from calcium and barium, which see) .

Sulphur

Sulphur exists in minerals either without oxygen, as in the sul phides, or with oxygen, as in the sulphates. These two types of sulphur compounds require different tests.

Tests for Sulphur in Sulphides

1. Open Tube Test. Sulphides when heated in the open tube give off sulphur dioxide gas, which escapes with the current of air from the upper end of the tube. Its presence can be detected by its pungent and irritating odor. A piece of moistened blue litmus paper inserted into the upper end of the tube will turn red on account of the sulphurous acid formed.

2. Charcoal Test. The odor of sulphur dioxide may be ob tained when a sulphide is roasted on charcoal.

3. Fusion with Sodium Carbonate. When a sulphide is fused on charcoal with sodium carbonate, the residue, unless the heating has been too prolonged, will contain sodium sulphide. If the slag is removed and placed with a drop of water on a clean silver surface (a coin will serve), there will result a dark brown stain due to the formation of silver sulphide.

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4. Treatment with Nitric Acid. Some sulphides are com pletely soluble in nitric acid, yielding sulphuric acid in the solution. This can be proved by adding a little barium chloride solution and obtaining the white precipitate of barium sulphate. In other cases the sulphur does not go into solution but separates as a spongy mass, usually black in color, that floats on the solution. Its identity is easily established by removing it and burning it in a flame.

5. Treatment with Hydrochloric Acid. Some sulphides are soluble in hydrochloric acid yielding hydrogen sulphide gas.

Tests for Sulphur in Sulphates

The test for sulphuric acid depends upon whether the sulphate is soluble or insoluble in acids.

1. Test for a Soluble Sulphate. If the sulphate is soluble, treat it with hydrochloric acid, and to the resulting solution add a little barium chloride. A heavy white precipitate of barium sulphate will result.

2. Test for an Insoluble Sulphate. Powder the mineral,

mix with sodium carbonate and charcoal dust and fuse on charcoal in the reducing flame. The charcoal serves to reduce the sulphate to a sulphide, so that the resulting slag contains sodium sulphide. When the fused mass is placed with a drop of water on a clean silver surface, a dark brown stain of silver sulphide will form. It is to be noted that a sulphide would yield the same test (see above), so that it is necessary to make certain that the mineral being tested does not belong to that chemical group.

Tantalum

There is no simple test for tantalum. It is usually associated, however, with niobium (see page 114).

Tellurium

1. Test with Sulphuric Acid. When a telluride is heated in

concentrated sulphuric acid, it gives a deep crimson color to the solution. The color will disappear if the acid is heated too hot, or if after cooling it is diluted with water.

Titanium

2. Charcoal Test. When heated on charcoal a white sublimate of Te02 is formed which somewhat resembles antimony oxide. It is volatile and when touched with the reducing flame gives a pale greenish color to it.

3. Plaster Tablet Test. On a plaster tablet tellurium minerals when heated give a purplish brown sublimate.

Tin

1. Reduction to Metallic Globule. Take a small amount of the finely powdered mineral and mix it with five or six volumes of sodium carbonate and considerable charcoal dust and fuse in tensely on charcoal in the reducing flame. Small bright globules of metallic tin will result. They become covered with an oxide coating on cooling. A white and difficultly volatile tin oxide coating will form on the charcoal. If the tin globule is treated with a little concentrated nitric acid, it will be converted into a white powder, which is metastannic acid.

Titanium

1. Reduction Test in Hydrochloric Acid. A comparatively concentrated hydrochloric acid solution containing titanium will become pale violet in color when it is boiled with a few grains of metallic tin. The hydrogen liberated by the action of the acid on the tin is a reducing agent and forms TiCl3 in the solution which gives this color. The color is not a strong one, and the solution may have to be evaporated nearly to dryness in order to show it distinctly. Most titanium minerals are insoluble in hydrochloric acid and must first be thoroughly fused with sodium carbonate in order to bring the titanium into soluble form. The fusion is best done by introducing the finely powdered mineral into a sodium carbonate bead made on a platinum wire. Several such beads should be used.

2. Test with Hydrogen Peroxide. Fuse the mineral with sodium carbonate; dissolve in equal amounts of concentrated sulphuric acid and water. When cold, dilute the solution and add a few drops of hydrogen peroxide. The solution will become yellow to amber in color.

Manual Of Mineralogy

Tungsten

1. Reduction Test in Hydrochloric Acid. Treat a tungsten mineral with hydrochloric acid. If it is decomposed by the acid a yellow precipitate of tungstic oxide, W03, will result. Add to the acid a few grains of metallic tin and boil. The hydrogen set free by the action of the hydrochloric acid on the tin serves as a reducing agent and converts the yellow W03 to a blue precipitate which is a mixture of the two oxides W03 and W02. On continued reduction the oxide becomes all W02 and is brown in color. The test is similar to the one for niobium, but is to be distinguished from that, since the blue color in the tungsten test does not disappear on dilu tion of the solution; and further, it turns to brown on continued reduction.' If the tungsten mineral is not attacked by hydro chloric acid, its powder must first be thoroughly fused with sodium carbonate. The resulting mass is powdered and digested with water, which will dissolve the sodium tungstate formed during the fusion. After filtering the reduction test is made as described above.

Uranium

1. Bead Tests. The tests for uranium consist in the colors it imparts to the fluxes (see page 100). The yellowish green color given to the salt of phosphorus bead when heated in the oxidizing flame is the most characteristic.

Vanadium

1. Bead Tests. The tests for vanadium consist in the colors it imparts to the fluxes (see page 100). The amber color given to the salt of phosphorus bead when heated in the oxidizing flame is the most characteristic.

2. Test with Hydrogen Peroxide. To an acid solution of a vanadate add a little hydrogen peroxide and the solution will assume a reddish brown color, due to the presence of pervanadic acid.

Zinc

Zinc

1. Oxide Coating on Charcoal. Metallic zinc is easily ob tained from the zinc minerals by fusing them with sodium carbonate on charcoal in the reducing flame. But, since the metal is volatil ized at a temperature considerably below that of the blowpipe flame, no metallic globule can be formed. The metallic zinc is therefore all volatilized, and, meeting the oxygen of the surrounding air, is converted into the oxide, ZnO, which drops upon the charcoal as a nonvolatile coating, which is yellow when hot but white when cold. The coating deposits very close to the fusion. It may frequently be obtained in more distinct form by making the fusion on a loop of platinum wire, which is held about one-quarter of an inch from the surface of a charcoal block and the blowpipe flame so directed that the oxide coating is deposited upon the charcoal behind the bead. If the coating is moistened with a drop of cobalt nitrate and then heated intensely by the blowpipe flame, it will become dark green in color.

2. Flame Color. Some zinc minerals, when a fragment is held in the forceps and heated in the reducing flame, will show a char acteristic flame color. This is due to the burning in the flame of the metallic zinc which has been volatilized. It takes the form of momentary streaks or threads in the flame and has a pale greenish blue color.

Iv. Descriptive Mineralogy

Introduction

Descriptive Mineralogy should include first of all a description of the crystallographic, general physical and chemical characters of each mineral species, and should further give an account of its mode of occurrence and characteristic associations. The localities at which a mineral occurs in notable amount or quality should also be mentioned. In the case of minerals possessing an economic value, a brief statement of their uses is of interest. The order in which these various items are given under each mineral in this Section is as follows:

1. Chemical Composition.

2. Crystallization.

3. Structure.

4. General Physical Properties.

5. Tests.

6. Occurrence.

7. Use.

Descriptive Mineralogy should also point out the chemical and physical relationships existing between the different mineral species. It will be noted that many minerals fall into definite groups, the members of which have chemical and crystallographic features in common. The most scientific classification of minerals recognizes these facts and places the minerals having analogous chemical compositions together, and further groups them according to crystallographic and physical similarities. Short paragraphs will be found in various parts of this Section which explain more fully these relationships. The prominent chemical groups of this

Elements

classification and the order in which they are treated are given below:

1. Native Elements.

2. Sulphides, etc.

3. Sidpharsenites, etc.

4. Chlorides, etc.

5. Oxides.

6. Carbonates.

7. Silicates, Titanates.

8. Niobates, Tantalates.

9. Phosphates, etc.

10. Borates.

11. Uranates.

12. Sulphates, etc.

13. Tungstates, Molybdates.

At the end of the matter descriptive of individual species will be found small sections devoted to (a) Minerals of economic impor tance arranged according to the chief elements they contain; (b) Occurrence and association of minerals; (c) Table of minerals ar ranged according to the systems of crystallization.

Elements

Comparatively few of the elements are found in the native state, and moreover, these are in general rare in occurrence. The elements occurring as minerals may be divided into three classes: (1) Nonmetals, (2) Semimetals and (3) Metals. The important minerals among the nonmetals are diamond, graphite and sul phur. The semimetals — tellurium, arsenic, antimony and bis muth — belong together in a crystal group, all of them showing rhombohedral crystals with closely agreeing fundamental angles. The Gold Group is the most important one among the metals, including the isometric minerals, — gold, silver and copper. An other group contains the rare metals platinum and iron.

Manual Of Mineralogy

I. Nonmetals

Diamond

Composition. Pure carbon.

Crystallization. Isometric; normal. Crystals are usually octahedral in habit, but the faces are commonly curved or pitted (Fig. 206). Curved faces of the hexoctahedron are frequently observed (Fig. 207). Cubic and dodecahedral planes rare. Twins, with the octahedron as twinning plane (Fig. 208) ; often flattened.

Fig. 206.

Fig. 207.

Fig. 208

Fig. 209.

Structure. Usually in crystals, but commonly distorted into elongated and irregular forms. At times in spherical forms with radiating structure. Rarely massive.

Physical Properties. Perfect cleavage parallel to the octa hedral faces. H. 10 (hardest substance known). G. 3.5. Luster adamantine or greasy. Usually colorless or pale yellow.

Diamond

Also pale shades of red, orange, green, blue and brown. Rarely in deep shades of blue, red or green; at times black. Usually transparent but may be translucent or opaque. Very high index of refraction (diamond 2.42, quartz 1.55). Strong disper sion of light. Electrified by friction and becomes phosphorescent when rubbed with a cloth. Some stones after exposure to sunlight give off a phosphorescent glow in the dark.

Varieties. Ordinary. In rounded crystals, some of which are perfectly transparent and colorless (first water). Others are faintly colored in various shades and frequently contain inclusions and are flawed. Bort. In rounded spherical forms with radiating structure or made up of confused crystalline aggregates; usually gray, brown or black in color and translucent to opaque. Frag ments of crystals that are unavailable for cutting are also frequently called bort. Carbonado or black diamond. Massive with crystal line structure or granular to compact without cleavage. Black or grayish black ; opaque.

Tests. To be distinguished by its great hardness, its adaman tine luster and its octahedral cleavage. Burns at a high tempera ture to C02 gas, leaving no ash. Will burn readily in oxygen gas, giving off a brilliant light.

Occurrence. The diamond is a rare mineral. It has been found in many different localities, but only a few have furnished the mineral in notable amount. Most commonly the diamond is found in the sands and gravels of stream beds, where it has been preserved by its great hardness"lmd fairly high specific gravity. In South Africa and recently in Arkansas it has been found embedded in masses of an igneous rock, known as peridotite. Three countries have up to the present furnished practically the entire world's output of dia monds, namely, India, Brazil, and South Africa.

The important diamond fields of India are located in the eastern and southern portions of the peninsula. Many of the famous old diamond fields in this region are now abandoned, but work is still carried on by the natives in the mines in a district lying to the south of Allahabad and Benares. Many of the world's famous diamonds were found in India, but at present the yield is small.

Diamonds were discovered in Brazil in the first half of the eight eenth century, and have been mined there ever since. At present, however, the production is comparatively small. They are found in the stream gravels in several different districts, the two most im-

Manual Of Mineralogy

portant being located in the provinces of Minas Geraes and Bahia. The city of Diamantina, Minas Geraes, is situated in the center of the most productive field, the diamonds being found chiefly in the gravels of the Rio Jequitinhonha and Rio Doce. Extensive upland deposits of diamond-bearing gravels and clays are also worked.

About 96 per cent of the world's output of diamonds comes at present from South Africa. The first diamonds were discovered in the gravels of the Vaal River in 1867. The diamond-bearing gravels covered a considerable area but were not very thick. Later the diamonds were discovered embedded in the rock of several volcanic necks located near the present town of Kimberly in Griqualand- West, south of the Vaal River, near the boundary of the Orange Free State. The diamonds in this district were first discovered in the soil resulting from the disintegration of the underlying diamond bearing rock. This soil- was colored yellow hv iron oxides, and was known as the "yellow ground." The underlying, undecomposed peridotite rock from which the diamonds are obtained at present is called the "blue ground." The principal mines are the Kimberly, Du Toitspan, De Beers and Bultfontein, near Kimberly, the Jagersfontein in the Orange Free State, and the Premier "in the Transvaal. The mines were originally worked as open pits, but, as they have increased in depth, underground methods have been adopted. The blue rock containing the diamonds is brought to the surface, crushed into coarse fragments and spread out on platforms to gradually dis integrate under atmospheric influences. The resulting gravel is washed over and concentrated, the diamonds being finally separated on shaking tables that have been coated with grease, to which the diamond crystals stick, while the rest of the material is washed away. Diamonds have also recently been discovered in alluvial deposits near Liideritz Bay, South West Africa.

Diamonds have been found sparingly in various parts of the United States. Small stones have occasionally been discovered in the stream sands along the eastern slope of the Appalachian Moun tains from Virginia south to Georgia. Diamonds have also been reported from the gold sands of northern California and southern Oregon. Sporadic occurrences of diamonds have been noted in the glacial drift in Wisconsin, Michigan and Ohio. In 1906 the first diamond was found at a new locality situated near Murfreesboro, Pike County, Aransas. The stones are found here not only in the detrital soil but also embedded in the underlying peridotite rock in a manner quite similar to that of the South African occurrence.

General. The diamond is the most important of the gem stones. Its value depends upon its hardness, its brilliancy, which is due to its high index of refraction, and to its "fire," which is due to its strong dispersion of light into the prismatic colors. In general the most

Diamond

valuable stones are those which are flawless and colorless or possess a "blue-white" color. A faint straw-yellow color, which diamond often shows, detracts much from its value. Deep shades of yellow, red, green or blue are greatly prized, and fine stones of these colors bring very high values.

The diamond is cut by first cleaving off any undesirable or flawed portions of the crystal and then grinding facets upon it by use of diamond powder. The crystal is fixed at the end of a stick by means of soft solder, leaving the part projecting which is to be cut. A cir cular plate of soft iron is then charged with diamond dust, and this by its revolution grinds and polishes the stone. Most diamonds are cut into the form known as the brilliant (see Fig. 209). This is a stone cut with a large eight-sided facet on top and a series of small inclined faces around it. The lower half consists of steeply inclined faces giving the stone on this side a pyramidal shape. The depth of a brilliant is nearly equal to its breadth, and it, therefore, can only be cut from a thick stone. Thinner stones, in proportion to the breadth, are cut into what is known as the rose diamond. This is a stone which has its upper surface covered with small triangular facets. Its lower surface may be one plane face, or the cutting of the upper half may be duplicated. With exceptional-shaped stones other cuttings are used.

The value of a cut diamond depends upon its color and purity, upon the skill with which it has been cut and upon its size. A onecarat stone weighs 205 milligrams, and if cut in the form of a brilliant would be 6.25 millimeters in diameter and 4 millimeters in depth. A two-carat stone of the same quality would have a value three or four times as great.

Faunous Stones. The older famous diamonds include the follow ing: the Kohinoor, weighing 106 carats, is one of the crown jewels of Great Britain; the Regent or Pitt, weighing 136 carats, belonging to France; the Orloff, which is mounted in the Russian imperial scepter, weighs 193 carats; Austria owns the Florentine yellow diamond, which weighs 139 carats; the Star of the South, weighing 125 carats, is said to be in India.

Large stones found more recently in South Africa include the following: the Victoria or Imperial, which weighed 457 carats when found, and 230 when cut. It was, however, later recut, its present weight being 180 carats. The Stewart weighed before and after cutting 288 and 120 carats respectively. The Tiffany diamond, which is of a brilliant yellow color, weighs 125 carats. The Colenso diamond, presented to the British Museum in 1887 by John Ruskin, weighs 129| carats. The Excelsior diamond, found at Jagersfontein in 1903, is now known as the Jubilee, and weighs 239 carats. The Cullinan or Premier diamond was found at the Premier Mine, Trans-

Manual Of Mineralogy

A'aal, and was the largest stone ever found, weighing 3024 carats or 1.7 pounds troy, and measured 4 by 2§ by 2 inches. This stone was presented to King Edward VII by the Transvaal Government and has been cut into 9 large stones, the larger ones weighing 516, 309 92 and 62 carats respectively, and into 96 smaller brilliants.

Name. The name diamond comes from the Greek word adamas, meaning "invincible."

Use. In addition to its wide use as a gem, the diamond is extensively used as an abrasive. Crystal fragments are used to cut glass. The fine powder is employed in grinding and polishing diamonds and other stones. The noncrystalline, opaque varieties, especially that known as carbonado, are used in the bits of diamond drills. These drills are frequently employed in mining operations to explore the rocks and to determine the position and size of ore bodies. Recently the diamond has been used in wiredrawing and in the making of tungsten filaments for electric lights.

Graphite

Composition. Carbon, like the diamond. Sometimes impure with iron oxide, clay, etc.

Crystallization. HexagQlIiombohedral. In tabular ciystals with hexagonal outline. Prominent basal plane. Distinct planes of other forms very rare. Rhombohedral symmetry some times shown by triangular markings on base.

Structure. In foliated masses; scaly; granular to compact; earthy. Sometimes in globular forms with radiated structure.

Physical Properties. Perfect basal cleavage. H. 1—2 (readily marks paper and soils the fingers). G. 2.2. Luster metallic, sometimes dull earthy. Black color with brownish tinge. Black streak. Greasy feel. Folia flexible but not elastic.

Tests. Infusible. Very refractory in its chemical nature. Recognized by its color, foliated structure and softness. Dis tinguished from molybdenite by the brownish tinge to its black coloi (molybdenite has a blue tone) and the lack of chemical tests.

Occurrence. Graphite most commonly occurs in metamorphic rocks, such as crystalline limestones, schists and gneisses. It mav

Graphite

occur as large crystalline plates inclosed in the rock or disseminated in small flakes in sufficient amount to form a considerable proportion of the rock. In these cases, it has probably been derived from carbon material of organic origin which has been converted into graphite during the metamorphism of the rock. Instances are known in which coal beds, under influence of strong metamorphic action, such as the intrusion into them of an igneous rock, have in a greater or less degree been converted into graphite. Examples of such an occurrence are to be found in the graphitic coals of RhodeIsland, and in the coal fields of Sonora, Mexu;o. Graphite also occurs in fissure veins associated with calcite, quartz, orthoclase, pyroxene, etc. An example of such veins is to be found in the deposits at Ticonderoga, NewYork. Here the veins traverse a gneiss and besides the graphite contain quartz, biotite, orthoclase, tourmaline, apatite, pyrite, titanite, etc. The graphite may have been formed in these veins from hydrocarbons introduced into them during the meta morphism of the region and derived from the surrounding carbon bearing rocks. Graphite occurs occasionally as an original constitu ent in igneous rocks. It has been observed in the basalts of Ovifak, Greenland, in a nepheline syenite from India, in a granite pegmatite from Maine, in meteorites, etc.

The most productive deposits of graphite at present are on the island of Ceylon, where it occurs in coarsely foliated masses in veins in gneiss. It occurs in large amounts in various localities in Austria, Italy, India, Mexico, etc. Graphite is found in quantity with schistose rocks in Madagascar. The chief deposits in the United States are in the Adirondack region of New York, in Essex, Warren and Washington counties, particularly at Ticonderoga.

Artificial. Artificial graphite is manufactured on a large scale in the electrical furnaces at Niagara Falls. Anthracite coal or petro leum coke with a small amount of evenly distributed ash is subjected to the intense heat of the electrical current and converted into graphite. The output of artificial graphite is considerably in excess of that of the natural mineral.

Name. Derived from the Greek work "to write."

Use. Used in the manufacture of refractory crucibles for the steel, brass and bronze industries. Most of the graphite used hi this way is imported from Ceylon. Used widely, when mixed with oil, as a lubricant. Mixed with fine clay, it forms the "lead" of pencils. Much of the graphite used in the United States for this purpose comes from Sonora, Mexico. Used in the manufac ture of a protective paint for structuraTiron and steel works. Used

Manual Of Mineralogy

in the coating of foundry facings, for electrodes, stove polishes, in electrotyping, etc.

Sulphur

Composition. Sulphur; often impure with clay, bitumen, etc. Crystallization. Orthorhombic. Pyramidal in habit (Fig. 210). Often with two pyramids, brachydome and base in com bination (Figs. 211 and 212).

Fig. 211.

Fig. 212.

Structure. Often in irregular masses imperfectly crystallized. Massive, renifonn, stalactitic, as incrustations, earthy.

Physical Properties. H. 1. 5-2.5. G. 2.05-2.09. Res inous luster. Color sulphur-yellow, varying with impurities to yellow shades of green, gray and red. Transparent to opaque. Imperfect conductor of heat. When a fragment is held in the hand close to the ear it will be heard to crack. This is due to the expansion of the surface layers because of the heat from the hand, while the interior, on account of the slow heat conductivity, is unaffected. Crystals of sulphur should, therefore, be handled with care.

Tests. Fusible at 1 and bums with a blue flame giving strong odor of sulphur dioxide. Sublimes in C.T. giving a red to dark yellow liquid when hot, yellow solid when cold. Told by its yellow color and the ease with which it bums.

Occurrence. Sulphur often occurs in connection with active or extinct volcanoes where it has been derived from the gases given off in fumaroles. These may furnish sulphur as a direct sublimation product or by the incomplete oxidation of hydrogen sulphide gas.

Arsenic

It is also formed by the reduction of sulphates, especially gypsum. At times it is deposited from sulphur-bearing waters by the action of the so-called sulphur bacteria. Sometimes in connection with sulphides in metallic veins and derived from their oxidation. It is most commonly found in the Tertiary sedimentary rocks and most frequently associated with gypsum and limestone; often in clay rocks; frequently with bituminous deposits. Found in large de posits and in fine crystals near Girgenti, Sicily, associated with celestite, gypsum, calcite, aragonite, etc.; also in connection with the volcanoes of Mexico, Hawaii, Japan, etc. In the United States the most productive deposits are in Louisiana and Texas. In Calsasieu Parish, Louisiana, a bed of sulphur 100 ft. thick is found at a depth of between 300 and 400 ft. It is underlain by beds of gyp sum and salt. Similar deposits occur at Freeport and at Gulf, Texas. Sulphur also occurs in Wyoming, Utah and California.

Use. Used in the manufacture of sulphuric acid, in the manu facture of matches, gunpowder, fireworks, insecticides, foi vul canizing rubber, in medicine and in the preparation of wood pulp for paper manufacture.

Ii. Semimetals

Tellurium

Native tellurium with sometimes a small amount of selenium, gold, iron, etc. Hexagonal-rhombohedral. Crystals rare; usually minute hexagonal prisms with rhombohedral terminations. Com monly massive, columnar to fine granular. Perfect prismatic cleav age. H. 2-2.5. G. 6. 1-6.3. Metallic luster. Tin-white color. Gray streak. Wholly volatile B. B. Fusible at 1. On charcoal tinges reducing flame green and gives a white oxide coating. Heated with concentrated sulphuric acid gives deep red color to solution. A rare species, found usually associated with the rare tellurides of gold and silver. Occurs with sylvanite near Zalatna, Rumania; at various localities in Colorado. Tellurium has little commercial value.

Arsenic

Composition. Arsenic, often with some antimony and traces

of iron, silver, gold, bismuth, etc.

Crystallization. Hexagonal-rhombohedral . Crystals rare.

Manual Of Mineralogy

Structure. Usually granular massive, sometimes reniform and stalactitic.

Physical Properties. Perfect basal cleavage. H. 3.5. G. 5.7. Metallic luster. Color tin-white on fresh fracture, tarnishes on exposure to dark gray. Gray streak.

Tests. Volatile without fusion. B. B. on charcoal gives white volatile coating of arsenious oxide and odor of garlic. In O. T. gives volatile crystalline deposit of arsenious oxide. In C. T. gives arsenic mirror.

Occurrence. A comparatively rare species found in veins in crys talline rocks associated with silver, cobalt or nickel ores. Found in the silver mines of Freiberg, etc., in Saxony, at Andreasberg in the Harz Mts., in Bohemia, Rumania, Alsace, etc. Sparingly in the United States.

Name. The name arsenic is derived from a Greek word mean ing masculine, a term first applied to the sulphide of arsenic on account of its potent properties.

Use. Very minor ore of arsenic.

Antimony

Composition. Antimony, with (at times) small amounts of arsenic, iron or silver.

Crystallization. Hexagonal-rhombohedral. Distinct crystals rare.

Structure. Usually in granular masses showing distinct cleavage; radiated; botryoidal.

Physical Properties. Perfect basal cleavage. H. 3-3.5. G. 6.G-6.7. Metallic luster. Tin-white color. Gray streak.

Tests. Easily and completely volatile. Fusibility 1. When heated on charcoal gives a dense white coating of antimony trioxide. Heated in O. T. gives a white, slowly volatile sublimate of anti mony trioxide.

Occurrence. A rare species, found usually in connection with silver veins and associated with arsenic and antimony compounds. Occurs at Sala, Sweden; Andreasberg, Harz Mountains; at Pribram,

Bismuth

Bohemia; Allemont, France; Borneo; Chile; South Ham, Quebec; York County, New Brunswick, etc.

Use. Minor ore of antimony.

Bismuth

Composition. Bismuth, with sometimes small amounts of arsenic, sulphur, tellurium.

Crystallization. H exagonal-rhombohedrah Distinct crystals rare.

Structure. Usually laminated and granular; sometimes re ticulated or arborescent.

Physical Properties. Basal and rhombohedral cleavage. H.

2-2.5. G. 9.8. Sectile. Brittle. Metallic luster. Color silver-white with decided reddish tone. Streak silver-white, shining.

Tests. Fusible at 1. B. B. on charcoal gives metallic globule and yellow to white coating of bismuth oxide. The globule is somewhat malleable but cannot be hammered into as thin a sheet as in the case of lead. Mixed with potassium iodide and sulphur and heated on charcoal gives a brilliant yellow to red coating and under same conditions on a plaster tablet gives a chocolate-brown sublimate with underlying red. Recognized chiefly by its lami nated structure, its reddish silver color and its sectility.

Occurrence. A comparatively rare mineral, occurring usually in connection with ores of silver, cobalt, nickel, lead and sometimes tin. Found in the silver veins of Saxony; in Norway and Sweden; Corn wall, England. Important deposits occur in Australia and Bolivia. With the -silver and cobalt minerals at CnhaU, Ont.'irin Pann/ln; only sparingly in the United States.

Use. Ore of bismuth. The greater part of the bismuth of commerce is produced from the sulphide, bismuthinite, or from other ores that contain a small per cent of the metal. It is chiefly employed in the manufacture of low-fusing alloys which are used as safety plugs in boilers and in automatic fire sprinklers, etc. Its salts are used in medicine.

Manual Of Mineralogy

Iii. Metals

Gold Group. Isometric

Gold

Composition. Gold, commonly alloyed with small amounts of silver and at times with traces of copper and iron. Ordinarily, native gold contains varying amounts of alloyed silver up to 16 per cent. California gold contains between 10 and 15 percent of silver. The greater part of native gold is about 90 per cent "fine" or contains 10 per cent of other metals. Gold containing un usually high percentages of silver (25 to 40 per cent) is known as eleclrum. .

Crystallization. Isometric. Crystals are commonly octahe dral in habit, showing also at times the faces of the dodecahedron, cube, etc. (see Figs. 213, 214 and 215). Often in arborescent

Fig. 215.

Cube and Octahedron.

Fig. 214. Dodecahedron.

Fig. 213. Octahedron.

crystal groups with crystals elongated in the direction of an octahedral axis. Crystals irregularly distorted and passing into filiform, reticulated and dendritic shapes.

Structure. Usually in irregular plates, scales or masses. Seldom definitely crystallized.

Physical Properties. H. 2.5-3. G. 15.6-19.3 (becomes greater as the percentages of the other metals present decrease). Very malleable and ductile. Color various shades of yellow, de pending upon purity, becoming paler with increase in the percent age of silver present.

Gold

Tests. Easily fusible at 2.5-3. Insoluble in ordinary acids but soluble in a mixture of hydrochloric and nitric acids. To be distinguished from certain yellow sulphides (particularly pyrite and chalcopyrite) and from yellow flakes of altered micas by its malleability, its insolubility. and its great weight.

Occurrence. Although gold is a rare element, it is to be found widely distributed in nature, occurring in small amounts. Its presenea as a primary constituent of igneous rocks, more particularly of the acidic type, haTEeen abundantly proved. It is to be found most commonly in cmartz veins. It occurs in detrital sands and gravels in what are known as placer deposits. It is present in small amounts in sea water. It is important to note that gold occurs almost wholly as__tlie native metal, the only class of compounds which it forms in nature hong the tellurides .

The chief source of gold is the gold-quartz veins. It occurs in these veins usually as very small specks scattered uniformly through out the quartz gangue. The contents of these veins are in general considered to have been deposited from ascending mineral-bearing solutions. That gold is capable of solution and subsequent precipi tation by means of underground waters has been repeatedly demon strated. In the, ma j ority -o£ veins-the gold-is- so finely divided and uniformly -distributed that its presence in the ore cannot be detected with, the eye. It is interesting to note that with the value of gold at $20.67 a troy ounce, ore which contains one per cent of gold by weight would be worth $6028 to the ton, while an ore containing only 0.01 per cent of gold would still be a rich ore, having a value of $60 per ton. Ores are mined at a profit sometimes which contain only 0.001 per cent of gold and yield but $6 to the ton. So it might be quite impossible to detect the presence of gold in a valuable ore by any ordinary tests. A definite estimation of the amount of gold present by means of a careful assay is the only way usually to deter mine the value of an ore. But occasionally, under favorable con ditions, the gold may collect in larger amounts, in nests and pockets in the veins, occurring usually as irregular plates and masses between the crystals of quartz. In the quartz veins the gold is frequently associated with sulphides, particularly with pyrite. It is thought that the gold does not exist in any chemical combination with the pyrite, but has the same mechanical relation to it that it has to the quartz. The upper portions of the gold-quartz veins as a rule have been enriched in their values. The gold present in this upper zone was in part deposited contemporaneously with the formation of the vein, but frequently the greater part has been transported, either in solution or by mechanical settling, from that upper portion of the vein which has been gradually eroded away. And so the gold in

Manual Of Mineralogy

this part of the vein represents the concentration in a small space of the original gold content of a much greater length of vein. By the oxidation of the gold-bearing sulphides originally deposited in this portion of the vein the gold embedded in them has been set free, rendering the gold easy of extraction. Ores that contain the gold free from intimate association with sulphides are known as "freemilling" because their gold content can be recovered by amalgamation with the mercury of the plates over which the finely crushed ore runs from the stamp mill. Where sulphides are present in any quantity all of the gold cannot be recovered by amalgamation and a chemical process, either the cyanide or chlorination process, must be used, either alone, or in addition to the amalgamation.

In addition to occurring with quartz and pyrite, gold has been found associated with chalcopyrite, sphalerite, galena, stibnite, cinnabar, arsenopyrite, limonite, calcite, etc.

Gold, on account of its great weight, is mechanically sorted in running water from the lighter material of the sands and gravels in which it may occur. In this way a concentration frequently takes place in stream beds and gold placer deposits are formed. In general these deposits will be found where the current of the water has been suddenly checked and the heaviest particles of its load dropped in the bottom of the stream. Sand bars, etc., formed in this way may contain rich placer deposits. Irregularities in the bottom of a stream frequently act as natural riffles and catch behind them the heavier gold traveling along the bottom of the stream. In general, also, such deposits will be richer as the stream is ascended and the original veins from which the gold has been derived are approached. The larger masses of gold whieh have been rolled together by the action of the stream are called nuggets. These sometimes attain considerable size. The very fine gold which is known as float gold may be carried by the streams for long distances.

In California, at the close of the glacial epoch, large amounts of gold-bearing gravels were deposited in the stream beds. Subse quent changes in the elevation of the country and extensive lava flows have caused a rearrangement of the drainage, and in places these old gravel beds are to be found to-day upon the hillsides and are known as the hill gravels. In places they have been covered over with lava flows and so preserved from erosion. At Cape Nome, Alaska, the beach sands contained gold, where by the action of the waves the gold has been concentrated to form placer deposits.

The important gold-producing states and territories of the United States, are Colorado, Alaska, California, Nevada, South Dakota, Utah, Montana, Arizona and Idaho. There are several other states that also produce the metal, but in comparatively small amounts. The most important gold-producing districts of California are those of

Silver

the series of gold-quartz veins known as the Mother Lode which Lie along the western slope of the Sierras in Nevada, Amador, Calaveras, Eldorado, Tuolumne and Mariposa counties. Between one-third and one-half of California's gold production comes from placer de posits, mostly worked by dredging operations in Butte and Yuba counties. The gold of Alaska has been derived chiefly from placer deposits, but recently the vein deposits have been of increasing im portance. The chief producing districts are the Yukon Basin, the Fairbanks District and the Seward Peninsula, including Nome. Al though Colorado is one of the first states in the production of gold, a large part of its output comes from the Cripple Creek District in Teller County, where the gold occurs only sparingly native, but chiefly in the form of the tellurides, sylvanite and calaverite. The other chief producing counties are San Miguel and Ouray in the San Juan District, and Lake County, containing the Leadville District, and Gilpin, Clear Creek and Boulder counties in the Clear Creek District. The chief gold districts of Nevada are in Elko, Storey, Nye, and Esmeralda counties. The gold from South Dakota comes from the Black Hills, the Homestake Mine at Lead being the largest producer. The gold-producing districts of Utah are the Tintic and Bingham districts in Juab and Salt Lake counties respectively, and the Mercur District in Tooele County.

Important foreign gold-producing countries are as follows: South Africa, Australia. Russia. Mexico and Canada. The region known as the Rand, near .Johannesburg in t he Transvaal, South Africa, is the most productive gold district in the world. The gold occurs here scattered throughout inclined beds or "reefs" of a quartzose conglomerate, which has been mined in enormous amounts and to great depths. Australia has the following chief gold districts: Kalgoorlie in western Australia (largely tellurides), Ballarat and Bendigo in Victoria, Mount Morgan in Queensland and various fields in New South Wales. In Russia gold is mined in western Siberia and the Urals, in the Irkutsk Province, in Transbaikalia and Amur. The production of Mexico comes chiefly from the districts of Guana juato, El Oro and Dolores.

Silver

Composition. Silver, frequently containing small amounts of alloyed Conner and gold, more rarely traces of platinum, anti mony, bismuth, mercury.

Crystallization. Igometric. Crystals commonly distorted and in branching, arborescent or reticulated groups.

Manual Of Mineralogy

Structure. Commonly in irregular masses, plates, scales, etc.; at times as coarse or fine wire.

Physical Properties. H. =2.5-3. G. 10.1-11.1, pure 10.5. Malleable and ductile. Color silver-white, often tarnished to brown or gray-black.

Tests. Easily fusible at 2 to bright globule. No oxide coating on charcoal. Easily soluble in nitric acid, giving on addition of hydrochloric acicla curdy white precipitate of silver chloride, which turns dark on exposure to light. Deposited from its solution by action of a clean copper plate.

Occurrence. Occurs usually as small irregular flakes and masses disseminated through various vein minerals, often invisible. Found associated with native copper, galena, argentite, chalcocite, the ruby silvers, tetrahedrite, calcite, barite, etc. While native silver is not an uncommon mineral, the larger part of the world's output of the metal is obtained from its various compounds with sulphur, anti mony, arsenic, etc. Most of the native silver occurring in nature is probably secondary in its origin, having been derived by reduction from some of its compounds.

Native silver has been found in the United States with native copper in the copper mines of Lake Superior; in crystal groups at the Elkhorn Mine, Montana; in large masses in the silver mines at Aspen, Colorado. Is found, at present, in large quantit.ie.s-as- platy masses, associated with various cobalt and nickel minerals, aLCobalt, Ontario, Canada. An important silver ore in the mines of Chihua hua, Guanajuato, Durango, and Sonora, Mexico. Was found in large masses, one of which weighed 500 pounds, in the mines at Kongsberg, Norway. One of the ores of the silver mines of Saxony and Bohemia.

Use. Silver is used for ornamental purposes, for coinage, plat ing, etc. It is usually alloyed with copper. The standard silver coin in the United States containsmne part of copper to nine parts of silver.

Copper

Composition. Copper, often containing small amounts of silver, bismuth, mercury, etc.

Crystallization. Isometric. Tetrahexahedron faces common on crystals (see Fig. 216). Also cube and dodecahedron. Crys-

Copper

tals usually distorted and in branching and arborescent groups (see PI. IV).

Structure. Usually in irregular masses, plates, scales, etc. In twisted and wirelike forms.

Physical Properties. H. 2.5-3.

G. 8. 8-8.9. Highly ductile and mal leable. Color copper-red, usually dark and with a dull luster on account of tarnish.

Tests. Fuses at 3 to a globule, which becomes covered with an oxide coating on cooling. Dissolves readily in nitric acid, and the solution is colored a deep blue on addition of ammonium hydroxide in excess.

Occurrence. A mineral found widely distributed in copper veins, but usually in small amount. Associated with various copper min erals, most commonly with the oxidized ores, cuprite, malachite and azurite. Ordinarily is strictly a secondary mineral and is to be found only in the upper parts of copper veins.

The most notable deposit of native copper known in the world is on Keweenaw Peninsula in northern Michigan, on the southern shore of Lake Superior. The region is occupied by a series of igneous flows of trap rock interbedded with sandstone conglomerates. The whole series dips toward the north. The copper is found in veins intersecting this rock series; in the amygdaloidal belts at the top of the various trap flows; and as a cementing material in the sand stone couglomor.itp This last type has furnished the most impor tant ore deposits, some of which have been worked for considerably over a mile in vertical depth. Not only does the copper act as a ce ment to bind the conglomerate together, but it has often penetrated the quartz boulders of the rock to a depth of a foot or more. It is associated with such minerals as opidotc. datolite. calcite and various zeolites. The mines were worked superficially by the Indians, and have been actively developed since the middle of the eighteenth century. Most of the copper of the district occurs in very small irregular specks, but notable large masses have been found, one weighing 420 tons being discovered in 1857.

Sporadic occurrences of copper similar to that of the Lake Superior District have been found in the sandstone areas of the eastern United States, notably in New Jersey, and in the glacial drift over-

Fig. 216. Cube and Tetrahexahedron.

Manual Of Mineralogy

lying a similar area in Connecticut. Native copper occurs in small amounts, associated with the oxidized ores of Arizona, New Mexico and northern Mexico.

Use. The most important uses to which the metal is put are as an electrical conductor; in the manufacture of brass (an alloy of copper and zinc), of bronze (an alloy of copper and tin with frequently zinc) ; for sheet copper; and as copper sulphate, which is used in calico printing, in galvanic cells, etc.

Mercury, Amalgam (Ag,Hg) and Lead are rare metals.

PLATINUM-IRON GROUP Platinum

Composition. Platinum, usually alloyed with several per cent of iron and with smaller amounts of iridium, osmium, etc. The amount of metallic platinum present seldom exceeds 80 per cent.

Crystallization. Isometric. Crystals very rare. Commonly distorted.

Structure. Usually in small grains or scales. Sometimes in irregular masses and nuggets of larger size.

Physical Properties. H. 4-4.5 (unusually high for a metal) . G. 14-19 native; 21-22 when chemically pure. Malleable and ductile. Color steel-gray, with bright luster.

Tests. B. B. infusible. Unattacked by ordinary reagents; soluble in a mixture of hydrochloric and nitric acids. Deter mined by its high specific gravity, infusibility and insolubility.

Occurrence. Platinum is a rare metal which occurs almost ex clusively native (only one rare compound, sperrylite, PtAs2, being known). It is found in quantity in only a few localities, and then only in the stream sands, as placer deposits, where it has been pre served on account of its great weight and hardness. Occurs in the alluvial deposits associated with the rarer metals of the Platinum Group, gold, iron-nickel alloys, chromite, etc. Its original source is probably usually in peridotite rocks or the serpentine rocks resulting from their metamorphism. It occurs so sparingly dissemi nated thiuugh such itcEs7 however, that it is only after their disin tegration and the subsequent concentration of the platinum in the

Plate Iv.

Arborescent Cooper. Lake Superior.

Iron

resulting sands that workable deposits of the metal are formed. Placer deposits of platinum are therefore to be Iooked_JflJi.in the tnnimt.y nf rocksT

Practically the entire world's supply of platinum at present comes from the TTra] Mountains in Russia. The central and northern end of this range has large masses of altered peridotite rocks, and in the sands of the streams descending from it, chiefly on the eastern slope in Siberia, platinum is found in considerable quantity. The chief districts are near Nizhne Tagilsk, and farther to the north, Bogoslovsk.

Platinum was first discovered in the United States of Colombia, South America, where it received its name platina from plata (silver). It is to be found there in two districts near the Pacific coast. The chief district covers the greater part of the intendencia of Ghoc6, department of Cauca. The platinum occurs here with gold in placer deposits, and, while the fields are not largely productive at present, they may become so.

The only platinum found in the United States comes from the gold placer deposits of Oregon ancL-Califemia, but the yearly yield amounts to only a few thousand dollars in value.

Use. The uses of the metal depend chiefly upon its insolubility, infusibility and superior hardness. It is used for various scientific instruments such as crucibles, dishes, etc., in the chemical labora tory; to line the distilling apparatus in the manufacture of sul phuric acid; in the electrical industry for contacts, etc.; in jewelry, chiefly as the setting for diamonds; as anodes in the electrolytic chemical industry; for electric heating apparatus; for the measure ment of high temperatures by the use of thermoelectricity; for sparking plugs in explosive motors; in incandescent electric lights, in the manufacture of false teeth and in fillings for teeth; and in various chemical reactions which are facilitated by the use of finely divided platinum.

Iron

Native iron, with always some nickel and usually small amounts of cobalt and frequently traces of copper, manganese, sulphur, car bon, phosphorus, etc. Isometric. Practically always massive. H. 4-5. G. 7.3-7.8. Malleable. Metallic luster. Color steelgray to black. Strongly magnetic. Occurs very sparingly as terres trial iron, and in the form of meteorites. ound, included in basalt,

Manual Of Mineralogy

on the west coast of Greenland, varying in size from small dissemi nated grains to large masses. Has been noted in a few other locali ties with a similar association. Nickel-iron alloys have been found in the gold sands of New Zealand ( awaruite ), from Josephine County, Oregon ( josephinite ), and from the Fraser River, British Columbia ( souesite ). Most meteorites contain native iron. The metal some times forms practically the entire body of the meteorite, while at other times it forms a cellular mass, inclosing grains of chrysolite, etc. In the stony meteorites, iron is found disseminated through them in the shape of small grains. Meteorites are to be recognized usually by their fused and pitted exterior. At first they are coated with a film of iron oxide, which disappears, however, on continued exposure to the weather.

Iridium, Iridosmine, an alloy of iridium and osmium, and Palladium are rare metals in the Platinum-Iron Group.

Sulphides

The sulphides form an important group of minerals which in cludes the majority of the ore minerals. With them are classed the similar but rarer selenides, tellurides, arsenides and antimonides. The sulphides may be divided into two groups depending upon the character of the metal present: (1) Sulphides of the Semimetals, (2) Sidphides of the Metals.

SULPHIDES OF THE SEMIMETALS Realgar

Composition. Arsenic monosulphide, AsS Sulphur 19.9, arsenic 70.1.

Crystallization. Monoclinic. Short prismatic crystals, ver tically striated. (See Fig. 217.)

Structure. In crystals, coarse to fine granular, often earthy and as an incrustation.

Physical Properties. Cleavage parallel to clinopinacoid. H. 1.5-2. G. 3.55. Resinous luster. Color and streak red to orange. Transparent to opaque.

Orpiment

Tests. Fusible at 1. Easily volatile. Heated on charcoal yields a volatile white sublimate of arsenious oxide with character istic garlic odor. Roasted in 0. T. gives volatile crystalline subli mate of arsenious oxide and odor of sulphur dioxide. Characterized chiefly by deep red color and resinous luster.

Occurrence. A rare mineral, occurring usually with orpiment, As2S3. Also associated with other arsenic minerals, stibnite, and with lead, silver, and gold ores. Also occurs as a volcanic sublima tion product or as a deposit from hot springs.

Found associated with silver and lead ores in Hungary, Bohemia, Saxony, etc. Found in good crystals at Nagydg, Transylvania; Binnenthal,

Switzerland; Allchar, Macedonia. Occurs at Mercur, Utah and at Manhattan, Nevada. Found deposited from the geyser waters in Yellowstone Park.

Name. The name is derived from the Arabic, Rahj al ghar, powder of the mine.

Use. Was used in fireworks to give a brilliant white light when mixed with saltpeter and ignited. Artificial arsenic sulphide is at present used for this purpose.

Orpiment

Composition. Arsenic trisulphide, As2S3 Sulphur 39, arse nic 61.

Crystallization. Monoclinic. Crystals small and rarely distinct.

Structure. Usually foliated.

Physical Properties. Very perfect cleavage parallel to clinopinacoid. Folia flexible but not elastic. Sectile. H. 1.5-2. G. 3.4-3. 5. Resinous luster, pearly on cleavage face. Color lemon-yellow. Translucent.

Tests. Same as for realgar (which see). Characterized by its yellow color, perfect cleavage and foliated structure.

Occurrence. A rare mineral, associated usually with realgar and formed under similar conditions. Found in various places in Ru-

Manual Of Mineralogy

mania; in Kurdistan; in Peru, Japan, etc. Occurs at Mercur, Utah and at Manhattan, Nevada. Deposited from geyser waters in the Yellowstone Park.

Name. Derived from the Latin, auripigmenlum, "golden paint."

Use. For a pigment, in dyeing and in a preparation for the removal of hair from skins. Artificial arsenic sulphide is largely used in place of the mineral.

Stibnite

Composition. Antimony trisulphide, Sb2S3 Sulphur 28.6, antimony 71.4. Sometimes carries gold or silver.

Fig. 218. Fig. 219.

Crystallization. Orthorhombic. Slender prismatic habit, prism zone vertically striated. Crystals often steeply terminated. (See Fig. 219). Often in radiating groups. Crystals sometimes curved or bent (Fig. 218).

Structure. In radiating crystal groups or in bladed forms with prominent cleavage. Massive, coarse to fine columnar.

Bismuthinite

Physical Properties. Perfect cleavage parallel to brachypinacoid. H. 2. G. 4.55. Metallic luster, splendent on cleavage surfaces. Color and streak lead-gray.

Tests. Very easily fusible at 1. B. B. on charcoal gives dense white coating of antimony trioxide and odor of sulphur dioxide. When roasted in 0. T. gives nonvolatile white sublimate on bottom of tube and a white volatile sublimate as ring around tube. Heated in C. T. gives a faint ring of sulphur and below a red (when cold) deposit of oxysulphide of antimony. Characterized by its bladed structure, perfect cleavage in one direction, its lead-gray color and soft black streak.

Occurrence. Deposited by alkaline waters in connection usually with quartz. Found in quartz veins or beds in granite and gneiss. Sometimes occurs as a replacement in limestones and shales, probably owing its origin to hot spring deposits. Often associated with in trusive rocks. Associated with other antimony minerals, as the products of its decomposition, and with galena, cinnabar, sphalerite, barite and sometimes gold. Found in various mining districts in Saxony, Rumania, Bohemia, Tuscany, central France, etc. Occurs in magnificent crystals in Province of Iyo, island of Shikoku, Japan. Important deposits occur in the Province of Hunan, China; also in Borneo, Peru, Mexico. Found in quantity only sparingly in the United States, the chief deposits being in California, and Idaho.

Use. Used in various alloys, as antimonial lead for storage batteries, as type, pewter, babbitt and britannia metals and anti friction metal. The sulphide is employed in the manufacture of fireworks, matches, percussion caps, etc. Used in vulcanizing rubber. Used in medicine as tartar emetic and other compounds. Antimony trioxide is used as a pigment and for making glass.

Bismuthinite

Composition. Bismuth trisulphide, Bi2S3 Sulphur 18.8, bis muth 81.2.

Crystallization. Orthorhombic. In acicular crystals.

Structure. Usually massive, foliated or bladed.

Physical Properties. Perfect cleavage parallel to brachypinacoid. H. 2. G. 6. 4—6. 5. Metallic luster. Color and streak lead-gray.

Manual Of Mineralogy

Tests. Easily fusible (1). Roasted in 0. T. or B. B. on char coal gives odor of sulphur dioxide. Mixed with potassium iodide and sulphur and heated on charcoal gives characteristic yellow to red coating and treated similarly on a plaster tablet gives a choc olate-brown coating underlain by red. Resembles stibnite; rec ognized by the test for bismuth.

Occurrence. A rare mineral occurring commonly in veins that show definite relations to igneous rocks. Found in Cornwall and Cumberland, England; in Saxony, Sweden. Important deposits associated with tin and tungsten ores occur in Bolivia. From Beaver County in Utah, etc.

Use. An ore of bismuth. See under native bismuth.

Molybdenite

Composition. Molybdenum disulphide, MoS2 Sulphur 40, molybdenum 60.

Crystallization. Hexagonal. Crystals in hexagonal-shaped plates or short, slightly tapering prisms.

Structure. Commonly foliated massive or in scales.

Physical Properties. Perfect basal cleavage. Eaminm flex ible but not elastic. Sectile. H. 1. G. 4.75. Greasy feel. Metallic luster. Color lead-gray. Grayish black streak.

Tests. Infusible. Heated B. B. gives yellowish green flame. Roasted in O. T. gives odor of sulphur dioxide and deposit of thin plates of molybdenum oxide, crossing the tube above the mineral. Heated on charcoal in 0. F. gives a white coating of molybdenum oxide; when this coating is touched with R. F. turns to deep blue color. When heated with potassium iodide and sulphur on a plaster tablet gives a deep blue sublimate. Resembles graphite but is distinguished from it by having a blue tone to its color, while graphite has a brown tinge, and by its reactions for sulphur and molybdenum.

Occurrence. In pneumatolytic contact deposits with cassiterite, scheelite, wolframite, fluorite, etc. Also found in pegmatite and quartz veins associated with granite, gneiss, syenite, etc.; more rarely in limestones. Occurs with the tin ores of Bohemia; from various

Argentite

places in Norway; from New South Wales. Found in the United States in many localities, but usually not in commercial quantity. Found at Blue Hill, Maine; Westmoreland, New Hampshire; in Okanogan County, Washington. From various places in Ontario, Canada.

Use. An ore of molybdenum. See under wulfenite.

Sulphides, Etc., Of The Metals

The sulphides of the metals are divided into the following groups: A. Basic Division; B. Monosulphide Division; C. In termediate Division; D. Disulphide Division.

A. Basic Division

This division includes several rare compounds of silver or cop per with antimony or arsenic such as dyscrasite, Ag3Sb to Ag6Sb; domeykite, CujAs; algodonite, Cu&As; whitneyite, Cu9As.

B. Monosulphide Division

1. Galena Group. Isometric

Argentite. Silver Glance

Composition. Silver sulphide, Ag2S Sulphur 12.9, silver

Crystallization. Isometric. Cube, dodecahedron and octa hedron the most common forms. Crystals often distorted and arranged in branching or reticulated groups.

Structure. Commonly massive, platy, earthy or as a coating. More rarely in crystals.

Physical Properties. H. 2-2.5. G. 7.3. Easily sectile, can be cut with a knife like lead. Metallic luster. Color and streak blackish lead-gray. Streak shining. Bright on fresh surface but on exposure becomes dull black, due to the formation of an earthy sulphide.

Tests. Easily fusible at 1.5 with intumescence. When fused alone on charcoal in 0. F. gives off odor of sulphur dioxide and

Manual Of Mineralogy

yields a globule of pure silver. Distinguished by these tests and by its color, sectility and high specific gravity.

Occurrence. Argentite is the most important primary mineral of silver, although it may also have a secondary origin. Usually found in silver veins as small masses, often earthy or as a coating. Asso ciated with native silver, the ruby silvers, polybasite, stephanite and other silver minerals; also galena. In the United States it was an important ore in the mines of the Comstock Lode, Nevada; at present found in Nevada at Tonopah and elsewhere. Found also in some of the silver districts of Colorado. An important ore in the silver mines of Guanajuato. and elsewhere in Mexico; in Peru, Chile and Bolivia. Important European localities for its occurrence are Freiberg in Saxony, Joachimsthal in Bohemia, Schemnitz and Kremnitz in Czechoslovakia, Kongsberg in Norway.

Use. An important ore of silver.

Galena. Galenite

Composition. Lead sulphide, PbS Sulphur 13.4, lead 86.6. Almost always carries traces of silver sulphide, frequently enough to make it a valuable silver ore. At times also contains small amounts of selenium, zinc, cadmium, antimony, bismuth and copper.

Crystallization. Isometric. Most common form is the cube, octahedron sometimes as truncations to cube, more rarely as the simple form (Figs. 220, 221 and 222; see also A, pi. V). Dodec ahedron and trisoctahedron rare.

Fig. 220. Cube.

Fig. 221.

Cube and Octahedron.

Fig. 222.

Octahedron and Cube.

Structure. Commonly crystallized or massive cleavable; coarse or fine granular.

Physical Properties. Perfect cubic cleavage. H. 2.5-2.75. G. 7.4-7.6. Bright metallic luster. Color and streak lead-gray.

Plate V.

A. Galena with Dolomite, Joplin, Missouri.

B. Fluorite, Cumberland, England.

Galena

Tests. Easily fusible at 2. Reduced on charcoal to lead globule with formation of yellow to white coating of lead oxide. "When heated rapidly in the 0. F. the coating is heavier and con sists chiefly of a white volatile combination of oxides of lead and sulphur, which resembles the antimony oxide coating. Odor of sulphur dioxide when roasted on charcoal or in 0. T. When treated with strong nitric acid is oxidized to white lead sulphate. Determined chiefly by its high specific gravity, softness, black streak and cubic cleavage.

Alteration. By oxidation it is converted into the sulphate, anglesite, the carbonate, cerussite, or other compounds.

Occurrence. A very common metallic sulphide, associated with sphalerite, pyrite, marcasite, chalcopyrite, cerussite, anglesite, dolo mite, calcite, quartz, barite, fluorite, etc. The veins are commonly in igneous rocks or show a close connection with such rocks. Frequently found with silver minerals, often containing that metal itself and so becoming an important silver ore. A large part of the supply of lead comes as a secondary production from ores mined chiefly for their silver. Occurs most commonly in connection with limestones, either as veins or irregular deposits, or as replacement deposits. The re placement deposits in limestone are commonly accompanied by a dolomitization of the rock and may or may not be associated with igneous rocks. Galena is also found in contact metamorphic deposits.

The following are the important lead producing localities in the United States: Southeastern Missouri, in which the ore occurs in the form of beds with the mineral disseminated through the lime stone; southwestern Missouri, where it is associated with zinc ores, and is found in irregular veins and pockets in limestone and chert; and similarly but in smaller amount in Illinois, Iowa, and Wisconsin, rnm wharf the lead is derived chiefly from lead-silver de

posits, the greater part of which come from in Shoshone County; Utah, in connection With the sdver deposits of the Tintic and Park City districts; Colorado, chiefly from the lead-silver ores of the Leadville District.

The most famous foreign localities are, Freiberg, Saxony; the Harz Mountains; from Westphalia and Nassau; Pribram, Bohemia in Czechoslovakia; Cornwall, Derbyshire and Cumberland, England.

Name. The name galena is derived from the Latin galena, a name originally given to lead ore.

Use. Practically the only source of lead and an important ore of silver. Metallic lead is used chiefly as follows: for conver-

Manual Of Mineralogy

sion into white lead (a basic lead carbonate), winch is the principal ingredient of the best white paints, or into the oxides used in mak ing glass and in giving a glaze to earthernware; as pipe and sheets; for shot ; it is one of the ingredients of solder (an alloy of lead and tin), of type metal (an alloy of lead and antimony) and of lowfusion alloys consisting of lead, bismuth and tin.

The following rare tellurides belong in this group; hessile, Ag2Te; petzite altaile, PbTe.

2. Chalcocite Group. Orthorhombic

Chalcocite. Copper Glance

Composition. Cuprous sulphide, Cu2S Sulphur 20.2, cop per 79.8.

Crystallization. OrflmrfcypKi'p Usually in small tabular crystals with hexagonal outline. Striated parallel to the brachyaxis (Fig. 223). Often twinned in pseudohexagonal forms (Fig. 224).

Structure. Massive. Crystals very rare.

Physical Properties. Conchoidal fracture. H. 2.5-3. G. 5.5-5.8. Metallic luster. Color shining lead-gray, tarnishing on exposure to dull black. Streak grayish black.

Tests. Easily fusible at 2-2.5. In 0. T. or B. B. on charcoal gives odor of sulphur dioxide. Roasted mineral, moistened with hydrochloric acid, gives azure-blue flame. Soluble in nitric acid;

Sphalerite

and the solution with an excess of ammonia turns dark blue. Recognized by its massive structure, its high specific gravity, its color, softness, and black streak.

Occurrence. Chalcocite is a very valuable ore of copper and is widespread in its occurrence. In the majority of cases it is to be found in the enriched sulphide zone of copper veins and is clearly secondary in origin. It has been formed in various ways by the action of descending copper-bearing solutions upon the original sulphide minerals of the veins. In other cases, however, chalcocite is primary and has been deposited as a direct precipitation from ascend ing waters. Associated with bornite, chalcopyrite, covellite, tetrahedrite, enargite, malachite, pyrite, etc. Found in crystals in Corn wall, England, and Bristol, Connecticut. Found as an ore at Monte Catini, Tuscany; from Tsumeb, South West Africa; French Congo, Mexico, Peru, Chile, etc. Occurs in immense deposits at Butte, Montana. Found in Alaska at Kennecott, Copper River District.

Use. An important copper ore.

Stromeyerite

A sulphide of silver and copper or Ag2S.Cu2S. Ortho rhombic. Commonly massive. H. 2.6-3. G. 6.15-6.3. Me tallic luster. Color and streak grayish black. Fusible at 1.5. In O. T. gives odor of sulphur dioxide. Roasted mineral with hydro chloric acid gives azure-blue flame. Nitric acid solution with hydro chloric acid gives precipitate of silver chloride. A rare silver mineral found with other silver and copper ores.

3. Sphalerite Group. Isometric, Tetrahedral

Sphalerite. Zinc Blende, Black Jack

Composition. Zinc sulphide, ZnS Sulphur 33, zinc 67. Al most always contains at least a small percentage of iron replacing the zinc, but the amount of iron may rise as high as 15 to 18 per cent. Also frequently contains small amounts of manganese, cadmium, mercury, etc. (see p. 84).

Crystallization. Isometric; tetrahedral. Tetrahedron (Fig. 225), dodecahedron and cube common forms, but the crystals frequently highly complex and usually distorted or in rounded forms. Often twinned.

Manual Of Mineralogy

Structure. Usually massive cleavable, coarse to fine granular. Compact, botryoidal. Also in rounded crystal masses.

Physical Properties. Perfect dodecahedral cleavage. H. 3.5-4. G. 4-4.1. Nonmetallic and resinous to submetallic luster; also adamantine. Color white when pure, and green when nearly so. Commonly yellow, brown to black, darkening with increase in the amount of iron present. Transparent to translu cent. Streak white to yellow and brown.

Fig. 225.

Fig. 226.

Tests. Infusible with pure zinc sulphide to difficultly fusible with increase in amount of iron. Gives odor of sulphur dioxide when heated on charcoal or in 0. T. Decomposed in powder by warm hydrochloric acid with evolution of hydrogen sulphide gas, which may be detected by its disagreeable odor. Wien heated on charcoal gives a coating of zinc oxide (yellow when hot, white when cold) which is nonvolatile in oxidizing flame. Recognized usually by its striking resinous luster and perfect cleavage. The dark varieties (black jack) can be told by noting that a knife scratch leaves a reddish brown streak.

Occurrence. Sphalerite, the most important ore of zinc, is an extremely common mineral, especially as a constituent of metallic veins. In its occurrence and mode of origin it is closely allied with galena with which it is most commonly associated. Found widely distributed, but chiefly in veins and irregular masses in limestone rocks where the ore bodies have been formed largely by replacement processes. It is also found in veins in eruptive rocks; in contact metamorphic deposits; etc. Associated with galena, pyrite, marcasite, chalcopyrite, smithsonite, calcite, dolomite, siderite, etc.

Pentlandite

May carry silver or gold. Large deposits are found in the United States in Missouri, Colorado, Montana, Wisconsin, Idaho and Kansas. The chief locality for its production is the Joplin District in southwestern Missouri and in adjacent districts in Kansas and Oklahoma. Noteworthy European localities are at Alston Moor and other places in the lead-mining districts of northern England; Binnenthal, Switzerland, in fine crystals; at Schemnitz and other localities in the gold and silver-mining districts of Czechoslovakia and Rumania.

Name. The name blende is from the German, blind or decep tive, because while often resembling galena it yielded no lead. Sphalerite, for the same reason, is derived from a Greek word meaning treacherous.

Use. The most important ore of zinc. The chief uses for metallic zinc, or spelter, are in galvanizing iron, making brass, an alloy of copper and zinc, in electric batteries, and as sheet zinc. Zinc oxide, or zinc white, is used extensively for making paint. Zinc chloride is used as a preservative for wood. Zinc sulphate is used in dyeing and in medicine. Sphalerite also serves as the most important source of cadmium.

Alabandite

Manganese sulphide, MnS. Isometric; tetrahedral. Usually granular massive. Cubic cleavage. H. 3.5-4. G. 3.95. Submetallic luster. Color iron-black, tarnished to brown on exposure. Streak olive-green. Fusible at 3. Gives odor of sulphur dioxide when roasted in O. T. Soluble in hydrochloric acid with evolution of hydrogen sulphide gas. With sodium carbonate in O. F. gives opaque greenish blue bead (manganese). A rare mineral, occurring usually with gold or silver ores.

Pentlandite

A sulphide of iron and nickel Isometric. Massive granular. Octahedral cleavage. H. 3.5-4. G. 4.55-5. Me tallic luster. Yellowish bronze color. Black streak. Fusible at 1.5-2. Gives odor of sulphur dioxide in O. T. Magnetic on heating in R. F. Roasted mineral in O. F. colors borax bead reddish brown (nickel). Closely resembles pyrrhotite in appearance but to be flwtingnishcH hv the ontahedral cleavage. A rare mineral, found with chalcopyrite near Lillehammer, Norway, and with pyrrhotite and chalcopyrite in the nickel deposits at Sudbury, Canada.

Manual Of Mineralogy

Other minerals which are rare in occurrence that belong in this group are, melacinnabarite, HgS; tiemannite, HgSe; onofrite, ; color adoite, HgTe.

4. Cinnabar-Millerite Group. Hexagonal

Cinnabar

Composition. Mercuric sulphide, HgS Sulphur 13.8, mer cury 86.2. Usually impure from admixture of clay, iron oxide, etc.

Crystallization. Hexagonal-rhombohedral ; trapezohedral. Crystals usually rhombodedral7 often in penetration twins. Trapezohedral faces rare.

Structure. Usually fine granular massive; also earthy and as incrustations. Crystals rare.

Physical Properties. H. 2-2.5. G. 8.10. Adamantine luster when pure, to dull and earthy when impure. Color ver milion-red when pure, to brownish-red when impure. Scarlet streak. Transparent to opaque.

Tests. 'Wholly volatile when free from gangue. Gives black sublimate of mercury sulphide when heated alone in C. T. When carefully heated in C. T. with dry sodium carbonate gives globules of metallic mercury. Carefully roasted in 0. T. gives odor of sulphur dioxide and sublimate of metallic mercury. Recognized usually by color, streak and high specific gravity.

Occurrence. The most important ore of mercury, but found in quantity at comparatively few localities. Occurs filling: fissures, cavities, etc., usually in sedimentary rocks; frequently as impregna tions and "replacements m sandstone or limestone. Associated with pyrite, marcasite, sulphides of copper, stibnite, realgar, gold, calcite, barite, quartz, fluorite, etc. Alwaysiauad4n- the neighb'Mmod -pf igneous rock masses from which n is thought that the mercury was nCTfved. Deposited probably through the agency of ascending hot waters. The important-localities for the occurrence of cinnabar are at Almaden, Spain; Idria in Gorizia, Italy; Huancavelica in southern Peru; .Provinces of Kweichow and Hunan, China; New Idria in San Benito County, Napa County, and New Almaden in Santa Clara County, California; Terlingua, Brewster County, Texas. Hepatic

Greenockite

cinnabar is an inflammable variety with liver-brown color and some times a brownish streak, usually granular or compact.

Name. The name cinnabar is supposed to have come from India, where it is applied to a red resin*

Use. The only important source of mercury.

Covellite

Cupric sulphide, CuS. Hexagonal. Rarely in tabular hexagonal crystals with prominent basal plane. Usually massive. Perfect basal cleavage. H. 1.5—2. G. 4.59. Metallic luster. Color indigo-blue. Fusible at 2.5. Gives odor of sulphur dioxide in O. T. and much sulphur in C. T. The roasted mineral, moistened with hydrochloric acid and ignited, gives a blue flame (copper). When moistened with water shows a strong purple color. A rare mineral, found only in the enriched sulphide zone of copper deposits, associated with chalcocite, bornite, chalcopyrite, tetrahedrite, etc.; and in most cases, if not always, is secondary in its origin.

Greenockite

Composition. Cadmium sulphide, CdS Sulphur 22.3, cad mium 77.7.

Crystallization. Hexagonal; hemimorphic. Crystals hemimorpliic, showing prism faces and terminated usually below with ba-se and above with pyramids.

Structure. Usually pulverulent, as thin powdery incrusta tions. Crystals small and rare.

Physical Properties. H. 3-3.5. G. 4.9-5. Luster adaman tine to resinous, earthy. Color yellow.

Tests. Infusible. Yields odor of sulphur dioxide when heated B. B. or in 0. T. Decomposed by hydrochloric acid with the evolution of hydrogen sulphide gas, which may be detected by its disagreeable odor. Gives a reddish brown coating of cadmium oxide when heated with sodium carbonate on charcoal. Char acterized by its yellow color and pulverulent form.

Occurrence. Most common mineral containing cadmium but found only in a few localities and in small amount. Associated usually with zinc ores, often as a coating on sphalerite and smith-

Manual Of Mineralogy

sonite. Found in crystals at Bishopton, Renfrewshire, Scotland; with the zinc ores of southwestern Missouri and in Arkansas, also in Bohemia and Carinthia.

Use. A source of cadmium. Cadmium-bearing zinc ores fur nish the greater part of the metal produced. Cadmium is used in alloys for dental and other purposes. The sulphide serves as a yellow pigment.

Millerite. Capillary Pyrites

Composition. Nickel sulphide, NiS Sulphur 35.3, nickel

Crystallization. Hexagonal-rhombohedral.

Structure. Usually in hairlike tufts and radiating groups of slender to capillary crystals. Sometimes in velvety incrustations.

Physical Properties. Cleavage rhombohedral. H. 3-3.5. G. 5.65. Metallic luster. Pale brass-yellow; with a greenish tinge when in fine hairlike masses. Streak black, somewhat greenish.

Tests. Fusible at 1.5-2 to magnetic globules. Gives odor of sulphur dioxide when heated on charcoal or in 0. T. The roasted mineral colors the borax bead reddish brown in 0. F.

Occurrence. Occurs in various localities in Saxony, Westphalia and Nassau and in Bohemia; with hematite and siderite at Antwerp, N. Y.; with pyrrhotite at the Gap Mine, Lancaster County, Pennsyl vania; in calcite at St. Louis, Missouri, Keokuk, Iowa, etc.

Use. A subordinate ore of nickel.

Niccolite. Copper Nickel

Composition. Nickel arsenide, NiAs Arsenic 56.1, nickel 43.9. Usually with a little iron, cobalt and sulphur. .Arsenic frequently replaced in part by antimony.

Crystallization. Hexagonal; hemimorphic (?).

Structure. Usually massive. Crystals rare.

Physical Properties. H. 5-5.5. G. 7.5. Metallic lus ter. Color pale copper-red, (hence called copper-nickel) with gray to blackish tarnish. Brownish black streak.

Pyrrhotite

Tests. Fusible (2). When heated B. B. on charcoal a white volatile deposit of arsenious oxide forms and a garlic-like odor is given off. Gives to borax bead a reddish brown color (nickel). Characterized chiefly by its color.

Occurrence. Associated usually with cobalt, silver and copper minerals. Not very common. Found in the silver mines of Saxony, the Harz Mts., in Hessen-Nassau; at Cobalt, Canada, etc.

Use. A minor ore of nickel.

Pyrrhotite. Magnetic Pyrites

Composition. A ferrous sulphide containing variable amounts of dissolved sulphur and so varying in composition from Fe5S6 up to FeieSiy. FeiiSi2 is the usually accepted formula. Often carries a small amount of nickel.

Crystallization. Hexagonal. Crystals usually tabular, or sometimes pyramidal.

Structure. Practically always massive with granular or lamel lar structure.

Physical Properties. H. =4. G. 4.65. Metallic luster. Brownish bronze color. Black streak. Usually slightly magnetic, but sometimes scarcely at all so.

Tests. Easily fusible. Strongly magnetic after heating. B. B. or in 0. T. gives odor of sulphur dioxide. Little or no sulphur in C. T. Decomposed by hydrochloric acid, giving off hydrogen sulphide gas. Recognized usually by its massive struc ture and bronze color.

Occurrence. A common minor constituent of igneous rocks. Q L L i T i i" ' i" mnPi-in intimate association with haste igneous rocks from which it has been segregated by some form of magmatic differentiation. AnniiOwl with the ferromagnesian minerals of the rocks in which it occurs, and also with chalcopyrite, and ruclcel minerals~as pentlandite. millerite. etc. It is also found in contact metamorptuc deposits, in vein deposits, in pegmatites, etc. Found in large quantities in Norwray and Sweden, at Sudbury, Ontario, Canada. In Germany from Andreasberg in ffiS HiSFiT MtS. ; at Schneeberg, Saxony; Bodenmais, Bavaria. In the United States in crystals from Standish, Maine; was found at the Gap Mine,

Manual Of Mineralogy

Lancaster County, Pennsylvania; in considerable amount at Ducktown, Tennessee.

/"Name. Derived from a Greek word meaning reddish.

Use. Serves as an important ore of nickel, particularly at Sudbury, Ontario.

- ' In this group belongs also the rare mineral, wurtzite, ZnS, which differs from sphalerite, since it is hexagonal in crystallization.

C. INTERMEDIATE DIVISION Bornite. Purple Copper Ore, etc.

Composition. Cu5FeS4 Sulphur 25.5, copper 63.3, iron 11.2. Analyses of different specimens show quite a wide variation in the percentages of the elements present, copper ranging from 55 to 71 per cent. Analyses of the purest material, however, agree with the above formula.

Crystallization. Isometric. Crystals rare. Usually in rough cubes, sometimes in penetration twins. Dodecahedron and octa hedron at times.

Structure. Commonly massive.

Physical Properties. H. =3. G. 4.9-5.4. Metallic lus ter. Color brownish bronze on fresh fracture but quickly tarnish ing on exposure to variegated purple and blue and finally to almost black. Streak grayish black.

Tests. Easily fusible at 2.5. Gives odor of sulphur dioxide on charcoal or in 0. T. Yields only a very little sulphur in C. T. Becomes magnetic in R. F. If, after roasting, it is moistened with hydrochloric acid and heated, it gives an azure-blue flame (copper). Easily soluble in nitric acid with separation of sulphur; solution neutralized with ammonia gives red-brown precipitate of ferric hydroxide and blue color to filtrate. Characterized chiefly by its purple tarnish.

Occurrence. An important and widely occurring ore of copper, but usually with other copper minerals and in subordinate amount. It has been found as a primary constituent in igneous rocks and in pegmatite veins. Bornite and chalcopyrite are the two common

Lin N Mite

original copper minerals, from which other copper minerals have been derived through secondary action. It is also frequently, itself, a secondary mineral, formed in the upper, enriched zone of copper veins through the action of descending copper-bearing solutions, upon clialcopyrite. The minerals with which it is commonly asso ciated are chalcopyrite, chalcocite, enargite, malachite, azurite, pyrite, etc. It frequently occurs in intimate mixture with chal copyrite and chalcocite. Found in the United States at Butte, Montana. It was found in unusual crystals, associated with crys tallized chalcocite at Bristol, Connecticut. Occurs at Actom, Quebec, Canada. Found in Cornwall; Monte Catini, Tuscany, and in various other European countries. An important ore in Chile, Peru, Bolivia and Mexico.

Name. Bornite was named after the mineralogist von Born (1742-1791). Sometimes called horseflesh ore in reference to the color on the fresh fracture, or variegated copper ore or peacock ore because of its purple tarnish. Called for the latter reason erubescite by English mineralogists.

Use. An important ore of copper.

Linnasite

A sulphide of cobalt, Co3S4 or CoS.Co2S3 with the cobalt replaced in varying amount by nickel. Isometric. In small octahedral crystals or granular massive. H. 5.5. G. 4.9. Metallic lus ter. Color pale steel-gray. Grayish black streak. Fusible at 2. Gives odor of sulphur dioxide in 0. T. Fuses in R. F. to a magnetic globule. Roasted mineral colors the borax bead blue (cobalt). A rare mineral, found with chalcopyrite near Riddarhyttan, Sweden; with barite and siderite at Miisen, Prussia; with lead ores at Mine La Motte, Missouri.

Chalcopyrite. Copper Pyrites. Yellow Copper Ore

Composition. A sulphide of copper and iron, CuFeS2 Sul phur 35, copper 34.5, iron 30.5.

Crystallization. Tetragonal; sphenoidal. Crystals usually in unit sphenoids (Fig. 227), which because the vertical axis is close to unity (c 0.985) are very near to the isometric tetrahedron in angles. Steeper sphenoids (Fig. 228), and other more complex forms occasionally observed.

Manual Of Mineralogy

Structure. Usually massive, compact; at times in crystals. Physical Properties. H. 3.5. G. 4.2-4.3. Metallic lus ter. Color brass-yellow; often tarnished to bronze or iridescent. Streak greenish black.

Fig. 228.

Tests. Easily fusible to a magnetic globule. Gives odor of sulphur dioxide when heated B. B. or in 0. T. Gives sulphur in C. T. After roasting, and moistening with hydrochloric acid, gives an azure-blue flame. Readily decomposed by nitric acid, giving separated sulphur; solution made ammoniacal gives redbrown precipitate of ferric hydroxide and blue filtrate (copper). Recognized by its brass-yellow color, greenish black streak and its softness. Distinguished from pyrite by its being softer than steel and from gold by its being brittle. Known sometimes as "fool's gold," a term which is also applied at times to pyrite.

Occurrence. The most common ore of copper. Occurs widely distributed in metallic veins associated with pyrite, pyrrhotite, bornite, chalcocite, tetrahedrite, malachite, azurite, sphalerite, galena, quartz, calcite, dolomite, siderite, etc. It is commonly of primary origin and from it, by various alteration processes, many other copper minerals are derived. Also occurs as an original con stituent of igneous rocks; in pegmatite veins; in contact metamorphic deposits; disseminated in schistose rocks; etc. May carry gold or silver and become an ore of those metals. Often in subordinate amount with large bodies of pyrite, making them serve as low-grade copper ores. Chief ore of copper mines at Cornwall, England; Falun, Sweden; Rio Tinto, Spain; Sudbury, Canada: in South Africa, Chile, etc. Found widely in the- United States but usually in connection with other copper minerals in equal or greater amount; found at Butte, Montana; Bingham, Utah; various districts in California, Colorado, Arizona, etc.

Pyrite

Name. Derived from Greek word meaning brass and from pyrites.

Use. Most important ore of copper.

Stannite

A sulphide of copper, tin and iron, Cu2S.FeS.SnS2. Zinc at times also present. Tetragonal, sphenoidal, but pseudo-isometric through twinning. Practically always massive. H. —4. G.

4.4. Metallic luster. Color steel-gray. Streak black. Fusible at

1.5. Slightly magnetic after heating in R. F. After roasting, and moistening with hydrochloric acid, gives when ignited a blue flame (copper). Fused alone on charcoal gives a nonvolatile white coating of tin oxide. A rare mineral, found in various places in Cornwall and with the tin ores of Bolivia.

D. Disulphide Division

1. Pyrite Group. Isometric; Pyritohedral.

Pyrite. Iron Pyrites

Composition. Iron disulphide, FeS2 Sulphur 53.4, iron 46.6. Sometimes contains small amounts of nickel, cobalt and copper. Frequently carries minute quantities of gold (auriferous pyrite).

Fig. 229. Striated Cubes.

Fig. 230. Pyritohedron.

Crystallization. Isometric: pyritohedral. Most common crystal forms are the cube, the faces of which are usually striated, the stria? on adjacent faces being perpendicular to each other (Fig. 229); the octahedron, and the pentagonal dodecahedron,

Manual Of Mineralogy

known commonly as the pyritohedron (Fig. 230). Figs. 231 to 233 show characteristic combinations of these forms. Fig. 234 shows a penetration twin that is at times observed.

Structure. Often in crystals. Also massive, granular, reniform, globular and stalactitic.

a

Fig. 231.

Cube

and Pyritohedron.

Fig. 232. Octahedron and Pyritohedron.

Octahedron and Pyritohedron.

Physical Properties. Brittle. H. 6-6.5 (unusually hard for a sulphide). G. 4.95-5.10. Luster metallic, splendent. Color pale brass-yellow, becoming darker at times on account of tarnish. Streak greenish or brownish black.

Tests. Easily fusible (2.5-3) to a magnetic globule. Yields much sulphur in C. T. Gives off sulphur dioxide in 0. T. or B. B. on charcoal. Insoluble in hydrochloric acid. Fine powder completely soluble in nitric acid, but may yield separated sulphur when too rapidly decomposed. Distinguished from chalcopyrite by its paler color and the fact that it cannot be scratched by steel; from gold by its being brittle.

Fig. 234. Twinned Occurrence. Pvrite is the most com-

Pyntohedrons. mon 0f f sulphides. It has been formed

in neutral or alkaline solutions and at high temperatures (cf. marcasite, p. 167). It is a common vein mineral, occurring in rocks of all ages and types, being most common in the metamorphic and sedimentary rocks. It is associated with many minerals being found most frequently with chalcopyrite, sphalerite,

Smaltite-Chloanthite

galena, etc. Is widely distributed as an accessory rock mineral in both igneous and sedimentary rocks being either primary or sec ondary in its origin. Frequently widely disseminated in the sedi mentary rocks, also in contact metamorphic deposits. Important deposits of pyrite in the United States are in Prince William, Louisa and Pulaski counties, Virginia, where it occurs in large lenticular masses which conform in position to the foliation of the inclosing schists; in St. Lawrence County, New York; at the Davis Mine, near Charlemont, Massachusetts; in various places in California. Large deposits occur at Rio Tinto and other mines in Spain, also in Portugal.

Alteration. Pyrite is easily altered to oxides of iron, usually limonite. It is, however, in general much more stable than marcasite. Pseudomorphic crystals of limonite after pyrite are com mon. Pyrite veins are usually capped by a cellular deposit of limonite, termed gossan. Rocks that contain pyrite are unsuitable for structural purposes because the ready oxidation of the pyrite in them would serve both to disintegrate the rock and to stain it with iron oxide.

Name. The name pyrite is from a Greek word meaning fire, in allusion to the fact that when struck with steel it gives off brilliant sparks.

Use. Pyrite is often mined for the gold or copper associated with it. Because of the large amount of sulphur present in the mineral it is never used as an iron ore. It is chiefly used to furnish sulphuric acid and copperas (ferrous sulphate). Sulphuric acid is perhaps the most important of all chemicals, being used for many different purposes, some of the more important being in the puri fication of kerosene and in the preparation of mineral fertilizers. The gas S02 derived either through burning sulphur or by roasting pyrite is used extensively in the preparation of wood pul]) for manu facture into paper. Copperas is used in dyeing, in the manufacture of inks, as a preservative of wood, and for a disinfectant.

Smaltite-Chloanthite

Smaltite is cobalt arsenide, CoAs2; chloanthite, nickel arsenide, NiAs2. The two molecules are isomorphous and all gradations

Manual Of Mineralogy

between the two species occur. Isometric pyritohedral. Usually massive, granular. Octahedral cleavage. H. 5.5-6. G. 6.3- 6.8. Metallic luster. Color tin-white. Streak black. Fusible at 2-2.5. Roasted on charcoal give a volatile coating of arsenious oxide with characteristic garlic odor. In borax bead in O. F. give blue color (cobalt). Rare species, occurring with other cobalt and nickel minerals, often associated with silver and copper ores.

Cobaltite-Gersdorffite

Cobaltite is a sulpharsenide of cobalt, CoAsS; gersdorffite a sulpharsenide of nickel, NiAsS. The two molecules are isomorphous with each other, and may occur together in varying amounts. Usually, however, any specimen will be found to be near one or the other ends of the series. Iron is frequently present, replacing the cobalt or the nickel, and sometimes in considerable amount. Iso metric ; jjyritohedral. Cobaltite commonly in cubes, pyritohedrons and octahedrons, also massive. Gersdorffite usually massive. Cubic cleavage. H. 5.5-6. G. 5. 8-6.2. Metallic luster. Color, tinwhite, in cobaltite inclining to reddish tone. Streak black. Fusi ble 2-3. On charcoal give a voTaflftr white sublimate of arsenious oxide with characteristic garlic odor. In 0. T. give volatile crystal line sublimate of arsenious oxide with odor of sulphur dioxide. In O. F. in borax bead give deep blue color (cobalt); if gersdorffite con tains no cobalt, gives brown bead ( nickel). Rare minerals, cobaltite being the commoner. Found associated with other cobalt and nickel minerals and with silver and copper ores. Notable occur rences of cobaltite are at Tunaberg, Sweden, and Cobalt, Ontario, Canada.

Sperrylite

A platinum arsenide, PtAs2. Isometric; pyritohedral. Usually in small grains, or in almost microscopic crystal fragments. H. 6-7. G. 10.6. Metallic luster. Tin-white color. Black streak. Fusible at 2. Roasted on charcoal gives volatile white coating of arsenious oxide with characteristic garlic odor. Roasted in O. T., at first very gently, a platinum sponge is left, which is insoluble in any single acid. A very rare mineral and the only known compound of platinum occurring in nature. Found with chalcopyrite in a gold-quartz vein near Sudbury. Canada, and with coveliite at the Rambler Mine, Encampment, Wyoming. Found in large crystals at the Waterberg district in the Transvaal, South Africa.

Marcasite

2. Marcasite Group. Orthorhombic

Marcasite. White Iron Pyrites

Composition. Iron disulphide, like pyrite, FeS2 Sulphur 53.4, iron 46.6.

Crystallization. Orthorhombic. Crystals commonly tabular parallel to basal plane, showing also short prisms and low brachydomes (Fig. 235). The brachydomes usually striated parallel to the brachy-axis. Often twinned, giving coxcomb and spearshaped groups (Fig. 236). Closely related in crystal forms and habit to arsenopyrite.

Fig. 235.

Fig. 236.

Structure. Usually in radiating forms. Often stalactitic, having an inner core with radiating structure and covered on the outside with irregular crystal groups. Also globular, reniform, etc. More rarely in crystals.

Physical Properties. H. 6-6.5. G. 4.85-4.9. Metallic luster. Color pale yellow to almost white, yellow to brown tar nish. Streak grayish black.

Tests. Fusible (2.5-3) to a magnetic globule. B. B. on char coal or in 0. T. gives odor of sulphur dioxide. Much sulphur in C. T. When fine powder is treated by cold nitric acid, and the solution allowed to stand until vigorous action ceases and then boiled, the mineral is decomposed with separation of sulphur. Pyrite treated in the same manner would have been completely dissolved. Recognized usually by its pale yellow color, its crys tals or its fibrous structure.

Manual Of Mineralogy

Occurrence. Marcasite is found in metalliferous veins, frequently with lead and zinc ores. Also at times in sedimentary rocks. It is more unstable than pyrite, being easily decomposed, and is not nearly as common in its occurrence. It is deposited at temperatures below 450° C. and from acid solutions (cf. pyrite, p. 164). It is usually formed under surface conditions. It most commonly occurs as replacement deposits in limestone; often in concretions embedded in clays, marls, etc. Found abundantly in clay near Carlsbad and elsewhere in Bohemia; in various places in Saxony; in the chalk marl of Folkestone and Dover, England; with zinc and lead deposits of Joplin. Missouri, and of Mineral Point, Wisconsin; from Oiilpna- Illinois.

Name. Derived from an Arabic word, at one time applied 'generally to pyrite.

Use. To a slight extent as a source of sulphuric acid, etc. (

Arsenopyrite. Mispickel

Composition. Sulpharsenide of iron, FeAsS Arsenic 46, sulphur 19.7, iron 34.3. Sometimes cobalt replaces a part of the iron ( danaite ).

Fig. 238.

Crystallization. Orthorhombic. Usually diamondshaped crystals, formed by a short prism terminated by low brachydomes. The brachydomes are usually striated parallel to the brachy-axis (Fig. 237). Twinned at times, giving stellate groups; the different individuals of the twin groups being dis tinguished from each other by the direction of the striations upon them (Fig. 238). Agrees closely in angles and crystal habit with marcasite.

Sylvanite

1G9

Structure. In crystals. Massive, granular to compact.

Physical Properties. H. 5.5-6. G. 6-6.2. Metallic luster. Silver-white color. Black streak.

Tests. Fusible at 2 to a magnetic globule. B. B. on charcoal gives a volatile coating of arsenious oxide and a characteristic garlic odor. In 0. T. gives odor of sulphur dioxide and a volatile ring of arsenious oxide. In C. T. gives arsenic mirror. Recog nized usually by its silver-white color, its crystals and a test for arsenic.

Occurrence. Arsenopyrite is the most common mineral contain ing arsenic. It occurs with tin and tungsten ores in pneumatolytic deposits. In veins formed by deposition from hot waters, associated with silver ores, galena, sphalerite, pyrite, chalcopyrite, etc. Fre quently associated with gold. At times it occurs disseminated in crystalline rocks, limestones, serpentine, etc. Occurs in quantity at Freiberg and Munzig, Saxony; with tin ores in Cornwall, England; from Tavistock, Devonshire; in various places in Bolivia; Deky, Ontario. Q'lmwLu where it is mined as a gold ore: Roxbury,~Connecticut, etc.

Use. An ore of arsenic. Arsenious oxide is used in the manu facture of glass, as a poison and a preservative. Paris green, an arsenate and acetate of copper, is used as a poison and a pigment. Sulphides of arsenic are used for paints and fireworks.

3. Sylvanite Group

Sylvanite

Composition. Telluride of gold and silver The ratio of the amounts of gold and silver varies somewhat; when Au : Ag 1 : 1 Tellurium 62.1, gold 24.5, silver 13.4.

Crystallization. Monoclinic. Distinct crystals rare.

Structure. Usually bladed or granular. Often in skeleton forms deposited on rock surfaces and resembling writing in ap pearance.

Physical Properties. Perfect cleavage parallel to elinopinacoid. H. 1.5-2. G. 8-8.2. Brilliant metallic luster. Color silver-white. Streak gray.

Manual Of Mineralogy

Tests. Easily fusible (1). If a little of the powdered mineral is heated in concentrated sulphuric acid the solution assumes a deep red color (tellurium). When decomposed in nitric acid leaves a rusty-colored, spongy mass of gold, and the solution with hydrochloric acid gives white precipitate of silver chloride. WTith sodium carbonate on charcoal gives a globule of gold and silver. Determined, by above tests, by its silver color and good cleavage.

Occurrence. A rare mineral, found with gold ores at Offenbdnya and Nagydg in Transylvania; Ivalgoorlie, West Australia; Cripple Creek, Colorado.

Name. Derived from Transylvania, where it wTas first found.

Use. An ore of gold.

Calaverite

Composition. Gold telluride, AuTe2 Tellurium 55.97, gold 44.03. Silver usually present isomorphous with the gold, to a small extent.

Crystallization. Monoclinic. Crystals usually developed parallel to the ortho-axis and the faces of the orthodome zone deeply striated. Terminated at the ends of the ortho-axis with a large number of faces. Crystallization complicated. Twinning frequent.

Structure. Usually granular. Distinct crystals rare.

Physical Properties. H. 2.5. G. 9.35. Metallic lus ter. Silver-white color, sometimes with yellowish tarnish. Streak gray.

Tests. Easily fusible (1). If a little of the powdered mineral is heated in concentrated sulphuric acid the solution assumes a deep red color (tellurium). Alien decomposed by nitric acid leaves a rusty-colored, spongy mass of gold, and on addition of hydrochloric acid gives only a slight precipitate of silver chloride. Distinguished from sylvanite by small amount of silver present and by its lack of a cleavage.

Occurrence. Found with sylvanite and other tellurides in the Cripple Creek District, Colorado, and at Kalgoorlie, West Australia.

Jameson I Te

Name. Found originally at the Stanislaus Mine, Calaveras County, California, whence name.

Use. An ore of gold.

Other rare tellurides belonging to this group are krennerite, AuTe2, and nagyagite, a sulpho-telluride of lead and gold.

Sulpharsenites, Etc.

The minerals in this division are considered to be salts of the sulpho-acids of trivalent arsenic, antimony and bismuth. Vari ous types of these acids are found, such as H3ASS3, H2AsS2, HiAs2S5, etc. A subdivision includes the sulpharsenates, etc., being chiefly salts of the acid H3AsS<. The metals observed are most commonly copper, silver and lead; also at times iron, zinc and mercury.

Jamesonite. Feather Ore

Composition. Sulphantimonite of lead. There are appar ently several different compounds that are often designated as "feather ore." A formula suggested for jamesonite is 4PbS.FeS.- 3Sb2S,.

Crystallization. Orthorhoiabic.

Structure. Usually in acicular crystals or in capillary forms. Also fibrous to compact massive.

Physical Properties. Basal cleavage. Brittle. H. 2-3. G. 5.5-6. Metallic luster. Color and streak steel-gray to grayish black.

Tests. Fusible at 1. On charcoal gives a combination coating of lead and antimony oxides. Roasted in 0. T. gives sublimates of antimony oxides. Heated on charcoal with a mixture of potas sium iodide and sulphur gives a chrome-yellow coating of lead iodide. Recognized by above tests and characteristic fibrous structure. Difficult to distinguish from similar species (see below).

Occurrence. Jamesonite is found in ore veins, associated with other lead sulphosalts, with galena, stibnite, tetrahedrite, sphalerite, etc. Found in Cornwall, England, and from various localities in

Manual Of Mineralogy

Czechoslovakia, Rumania, Saxony, etc.; from Tasmania and Bolivia. Noted in the United States from Sevier County, Arkansas, and at Silver City. Pennington Co., South Dakota.

Similar Species. There are a number of minerals similar to jamesonite in composition and general physical characteristics whose relations to each other ha many cases are not thoroughly understood. These include such minerals as zinkenite, PbS.Sb2S3; plagionite, 5PbS.4Sb2S3; semseyite, 5PbS.2Sb2S3; boulangerite, 5PbS.Sb2S3; meneghinite, 4PbS.Sb2S3; geocronite, 5PbS.Sb2S3.

Boumonite

Composition. Sulphantimonite of lead and copper Sb2S6 or The relative amounts of the lead and copper present vary, but in general correspond closely to the ratio

Pb : Cu2 =2:1.

Crystallization. Orthorhombic. Crystals usually shortXvpnsmatic to tabular. Sometimes quite complex with many prism, pyramid and dome faces. Frequently twinned, giving tabular crystals with recurring re entrant angles in the prism zone (Fig. 239), whence the common name of cogwheel ore.

Structure. Massive; granular to compact; in crystals.

Physical Properties. H. 2.5-3. G. 5. 7-5.9. Metallic luster. Color and streak steel-gray to black.

Tests. Fusible at 1. B. B. on charcoal gives a combination coating of antimony and lead oxides. Roasted in O. T. gives sublimates of antimony oxides. Heated on charcoal with a mix ture of potassium iodide and sulphur gives a chrome-yellow coating of lead iodide. Decomposed with nitric acid, solution turns blue with excess of ammonia (copper). Recognized either by char acteristic crystals or above tests.

Occurrence. A rare mineral, found in veins with galena, tetrahedrite, stibnite, chalcopyrite, sphalerite, etc. Found at Neudorf and other localities in the Harz Mountains; Kapnikbanya in Rumania;

Proust I Te

Liskeard in Cornwall; from Bolivia; etc. Has been found, also, in various places in the United States, but not in notable amount or quality.

Pyrargyrite. Dark Ruby Silver

Composition. Sulphantimonite of silver, Ag3SbS3 or 3Ag2S.- Sb2S3 Sulphur 17.8, antimony 22.3, silver 59.8. Sometimes contains a small amount of arsenic. Compare proustite.

Crystallization. Hexagonal-rhomb'ohedral ; hemimorphic. Crystals prismatic with rhombohedral and scalenohedral termi nations. Usually distorted and often with complex development. Frequently twinned.

Structure. In crystals or massive; compact; in disseminated grains.

Physical Properties. Rhombohedral cleavage. H. 2.5. G. 5.85. Luster adamantine. Color usually dark red to black, in thin splinters deep ruby-red. Indian-red streak.

Tests. Fusible at 1. On charcoal gives dense white coating of antimony trioxide. After prolonged heating, coating becomes tinged with a reddish color near assay due to a small amount of volatilized silver. Odor of sulphur dioxide and coatings of anti mony oxides when heated in 0. T. Decomposed by nitric acid and solution with hydrochloric acid gives white precipitate of silver chloride. Characterized chiefly by its dark red color and streak.

Occurrence. A rare silver mineral associated with proustite, argentite, galena, calcite, etc. Primary in origin and commonly found in the upper portion of silver veins. Found in the silver mines at Andreasberg, Harz Mountains; at Freiberg, Saxony; Pribram, Bokgmia; in Guanajuato, Mexico; at Chanarcillo, Chile; in Bolivia. Found" in various silver veins in Colorado; Nevada, New Mexico, Idaho, etc.

Name. Derived from two Greek words meaning fire-silver.

Use. An ore of silver.

Proustite. Light Ruby Silver

Composition. Sulpharsenite of silver, AgjAsSa or 3Ag2S.As2S3 Sulphur 19.4, arsenic 15.2, silver 65.4. May contain a small amount of antimony. Compare pyrargyrite.

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Crystallization. Hexagonal-rhombohedral ; hemimorphic. Crystals commonly with prominent steep rhombohedrons and scalenohedrons. Often distorted and frequently complex in development.

Structure. Commonly massive, compact, in disseminated grains.

Physical Properties. Rhombohedral cleavage. H. 2-2.5. G. 5.55. Adamantine luster. Color ruby-red. Transparent to translucent. Red streak. High index of refraction.

Tests. Fusible at 1. Heated on charcoal gives volatile sub limate of arsenious oxide with characteristic garlic odor. In 0. T. gives odor of sulphur dioxide and volatile crystalline sublimate of arsenious oxide. In C. T. gives abundant sublimate of arsenic sulphide, reddish black when hot, reddish yellow when cold. With sodium carbonate on charcoal gives a globule of silver. Characterized chiefly by its ruby-red color and streak and its brilliant luster.

Occurrence. A rare mineral, with mode of occurrence and associa tions similar to those of pyrargyrite. Found in the silver mines of Saxony; Bohemia; at Chanarcillo, Chile, in fine crystals; common in the~silver_mines of Peru and Mexico. Found in Colorado in the silver mines of the San Juan Mountains and elsewhere; in various silver districts in Nevada, Idaho, etc.

Use. An ore of silver.

T etrahedrite-T ennantite . Composition

Crystallization,

Gray Copper. Fahlore

Tetrahedrite, Cu8Sb2S7 or 4Cu2S.Sb2S3 Sul phur 23.1, antimony 24.8, copper 52.1. Tennantite, CuuAs2S7 or 4Cu2S.As2S3 Sulphur 25.5, arsenic 17.0, copper 57.5. Antimony and arsenic are usually both present and the two species graduate into each other, so that no sharp line can be drawn between them. The copper is often replaced in varying amounts by iron, zinc, silver, mercury, lead, etc.

Isometric; tetrahedral. Habit tetrahedral.

Stephan I Te

Tetrahedron (Fig. 240), tristetrahedron, dodecahedron and cube the common forms.

Structure. Frequently in crystals. Also massive, coarse or fine granular.

Physical Properties. H. 3-4. G. 4.7-5. Metallic lus ter, often sjMendp.nt,. Color grayish black to black. Streak black.

Tests. Easily fusible at 1.5. On charcoal or in 0. T. gives tests for antimony or arsenic, or both. After roasting, and moisten ing with hydrochloric acid, gives azure-blue flame. Decomposed by nitric acid with separation of sulphur and antimony trioxide; solution made alkaline with ammonia turns blue. The two species are only to be told apart by testing for the presence of antimony and arsenic, and as both are often present in the same specimen a quantitative analysis may be necessary in order to positively determine to which end of the series it belongs. Recognized by its tetrahedral crystals, or when massive by its fine-grained structure and by its gray color.

Occurrence. Tetrahedrite is the most common member of the sulphosalt group and is widespread in occurrence and varied in association. Commonly found in copper or silver veins, usually as a primary constituent but at times it may be secondary in origin. Usually associated with chalcopyrite, pyrite, sphalerite, galena and various other silver, lead and copper ores. May carry sufficient silver to become an important ore of that metal (the highly argentif erous variety is known as freibergite) . Is found in the United States in various silver and copper mines in. Colorado, Nevada. Arizona, etc. Found in Cornwall, England; the Harz Mountains, Germany; Freiberg, Saxony; Pribram in Bohemia; various places in Rumania; in the silver mines of Mexico, f'eru and Bolivia.

Use. An ore of silver and copper.

Stephanite

Composition. Sulphantimonite of silver, Ag5SbSj or 5Ag2fe.- Sb2S3 Sulphur 16.3, antimony 15.2, silver 68.5.

Crystallization. Orthorhombic. Crystals usually short pris matic and tabular parallel to the base. Edges of crystals trun cated by various pyramids. Prism zone usually shows the four prism faces and the two of the brachypinacoid, all making nearly

Manual Of Mineralogy

60° angles with each other and so giving the crystals a hexagonal aspect. Also twinned in pseudohexagonal crystals. Crystals usually small.

Structure. Massive, in disseminated grams; crystallized.

Physical Properties. H. 2-2.5. G. 6. 2-6.3. Metallic luster. Color and streak iron-black.

Tests. Fusible at 1. B. B. on charcoal gives dense white sublimate of antimony trioxide and odor of sulphur dioxide. De composed by nitric acid, and if after filtering a little hydrochloric acid is added to filtrate, it gives a white precipitate of silver chlo ride. Recognized by its stout hexagonal crystals and the above tests.

Occurrence. A rare silver mineral of primary origin but charac teristically found in the upper portions of its veins. Found associa ted with other sulphantimonites of silver, galena, tetrahedrite, sphalerite, etc. Occurs at Freiberg and other localities in Saxony-; in Czechoslovakia; at Guanajuato and Arizpe, Sonora, etc., Mexico; in Chile. In the United States was an abundant ore at the Comstock Lode and other silver deposits in Nevada.

Use. An ore of silver.

Polybasite

Composition. Sulphantimonite of silver, AgSbSe or 9Ag2S- Sb2S3 Sulphur 15, antimony 9.4, silver 75.6. Copper replaces a part of the silver and arsenic replaces the antimony.

Crystallization. Monoclinic. Crystals are pseudorhombohedral in symmetry, occurring in short- hexagonal prisms, often thin tabular. Basal planes show triangular markings.

Structure. In crystals. Granular.

Physical Properties. H. 2-3. G. 6-6.2. Metallic lus ter. Color steel-gray to iron-black. Streak black.

Tests. Fusible at 1. B. B. on charcoal gives dense white coating of antimony trioxide with odor of sulphur dioxide. After decomposition by nitric acid, the filtrate with hydrochloric acid gives white precipitate of silver chloride. To be distinguished from other similar species chiefly by its crystals.

Enargite

Occurrence. A comparatively rare silver mineral, associated with other sulphantimonides of silver and with silver ores in general. Found in the silver mines of Mexico, Chile, Saxony and Bohemia. Found in the United States at the Comstock Lode, Nevada; near Ouray, Colorado; from Idaho, etc.

Name. Name is in allusion to the many bases contained in the mineral.

Use. An ore of silver.

Enargite

Composition. Sulpharsenate of copper, CU3A.SS4 or 3Cu2S- As2Sr, Sulphur 32.6, arsenic 19.1, copper 48.3. Antimony may replace in part the arsenic, and the species graduate toward Jamatinite (3Cu2S.Sb2S5).

Prismatic crystals with

Crystallization.

prism zone vertically striated

Structure. Columnar, bladed, massive.

Physical Properties. Perfect prismatic cleavage. H. 3. G. 4.43-4.45. Metallic luster. Color and streak grayish black to iron-black.

Tests. Easily fusible (1). B. B. on charcoal gives volatile white sublimate of arsenious oxide and characteristic garlic odor. In 0. T. gives white crystalline sublimate of arsenious oxide and odor of sulphur dioxide. Roasted on charcoal, then moistened with hydrochloric acid and again ignited, gives azure-blue flame. Characterized by its color, its cleavage and the above tests.

Occurrence. A comparatively rare mineral, found associated with other copper minerals, as chalcocite, bornite, tennantite, etc. From Bor, near Zajecar, Yugoslavia. Found abundantly at Morococha, Peru; also from Chile and Argentina; island of Luzon, Philippines. Found in considerable quantity with the copper ores at Butte, Mon tana. Occurs in the silver mines of the San Juan Mountains, Colorado.

Use. An ore of copper. Arsenic oxide also obtained from it at Butte. Montana.

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Chlorides, Etc.

The chlorides with the related bromides, iodides and fluorides are grouped into the following divisions: (1) Anhydrous Chlorides, etc.; (2) Oxychlorides, etc.; (3) Hydrous Chlorides, etc.

1. Anhydrous Chlorides, Etc.

Halite Group

The Halite Group includes the isometric minerals halite, NaCl; sylvite, KC1; cerargyrite, AgCl; embolite, bromyrite, AgBr.

Halite. Common Salt

Composition. Sodium chloride, NaCl Chlorine 60.6, so dium 39.4. Commonly contains impurities, such as calcium sul phate and calcium and magnesium chlorides.

Crystallization. Isometric. Habit cubic (Fig. 241). Other forms very rare.

Structure. In crystals or granular crystalline, in masses showing cubical cleavage, known as rock salt. Also massive, granular to compact.

Physical Properties. Perfect cubic cleavage. H. 2.5. G. 2.1-2.6. Trans parent to translucent. Colorless or white, or when impure may have shades of yellow, red, blue, purple. Readily soluble in water. Salty taste. Diathermanous.

Tests. Easily fusible at 1.5, giving strong yellow flame of sodium. After intense ignition B. B. residue gives alkaline reaction to moistened test paper. Readily soluble in water; solution made acid with nitric acid gives with silver nitrate a heavy white precip itate of silver chloride. Salty taste. Distinguished from sylvite (KC1) by its yellow flame color and by the latter having a some what more bitter taste.

Fig. 241.

Halite

Occurrence. A common and widely disseminated mineral, oc curring often in extensive beds and irregular masses, interstratified in rocks of all ages, in such a manner as to form a true rock mass. Associated with gypsum, sylvite, anhydrite, calcite, clay, sand, etc. Occurs also dissolved in the waters of salt springs, salt seas and the ocean.

The deposits of salt have been formed by the gradual evaporation and ultimate drying up of inclosed bodies of salt water. The salt beds formed in this way have subsequently been covered by other sedimentary deposits and gradually buried beneath the rock strata formed from them. The salt beds range from a few feet up to one hundred in thickness and have been found at depths of two thousand feet and more from the surface. The history of the formation of these salt beds is as follows: River waters contain a small but appreciable amount of various soluble salts. When these waters are collected in a sea which has no outlet, or in other words, a sea where the evaporation equals or exceeds the amount of water flowing in, there is a gradual concentration in the sea of the salts brought into it by the rivers. The sea water, therefore, in time becomes heavily charged with soluble salts, particularly sodium chloride. When the points of concentration of the various salts held in solu tion are reached, they will be deposited progressively upon the sea bottom, commencing with the most insoluble. This process may continue for a long period of time and ultimately a thick layer of salt and other soluble minerals, be formed on the bottom. The process may be interrupted by seasons of flood in which the sea water becomes freshened beyond the concentration point. Silt materials may be brought in at such times and deposited upon the bottom and so form beds of clay alternating with those of salt. Another mode of origin may have been as follows. A body of sea water was separated from the ocean by the gradual growth of a sand bar with the subsequent slow evaporation and concentration of the enclosed water. Such deposits of salt have been formed wherever favorable conditions occurred, and are now to be found buried in rock strata of all ages. At the present time similar deposits are being formed in the Great Salt Lake and the Dead Sea.

In the United States salt is produced, on a commercial scale, in some fifteen states, either from rock-salt deposits, or by evaporation of salt lake or sea waters. Beds of rock salt are found in New York State from the Oatka Valley in Wyoming County east to Morrisville, Madison County, and south of this line wherever wells have been driven deep enough to reach the beds. The important producing localities are near Syracuse, Ithaca, Watkins and Ludlowville, and at various places in Wyoming, Genesee and Livingston counties. Extensive deposits of salt occur in Michigan, chiefly in Saginaw,

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Bay, Midland, Isabella, Detroit, Wayne, Manistee, and Mason counties. Notable deposits are also found in Ohio, Kansas, Louisi ana. Salt is obtained by the evaporation of saline waters in Cali fornia, Utah and Texas.

Important foreign localities for the production of salt are to be found in Austrian Poland, Czechoslovakia, Bavaria, Prussia, Spain and Great Britain.

Use. The chief uses of salt are for culinary and preservative purposes. It is used also in the manufacture of soda ash (sodium carbonate), wliich is used in glass making, soap making, bleaching, etc., and in the preparation of sodium salts in general. Salt is used also in the extraction of gold by the chlorination process.

Sylvite

Composition. Potassium chloride, KC1 Chlorine 47.6, po tassium 52.4. Sometimes contains sodium chloride.

Crystallization. Isometric. Cube and octahedron frequently in combination (Fig. 242).

Structure. Usually in granular crystal line masses showing cubic cleavage; com pact.

Physical Properties. Perfect cubical cleavage. H. =2. G. 1.9. Transparent when pure. Colorless or white; also shades of blue, yellow or red from impurities. Readily soluble in water. Salty taste but more bitter than in the case of halite.

Tests. Easily fusible at 1.5, giving violet flame of potassium, which may be obscured by yellow flame due to sodium present. The yellow sodium flame may be filtered out by use of a blue glass, and the violet of the potassium rendered visible. After intense ignition, residue gives alkaline reaction on moistened test paper. Readily soluble in water; solution made acid with nitric acid gives with silver nitrate a heavy precipitate of silver chloride. Distin guished from halite by the violet flame color of potassium and its slightly bitter taste.

Cerargyrite

Occurrence. Has the same origin, mode of occurrence and asso ciations as halite (which see) but is much more rare. Found in some quantity and at times well crystallized in connection with the salt deposits at Stassfurt, Prussia; from Kalusz in Galicia, etc.

Name. Potassium chloride is the sal digestivus Sylvii of early chemistry, whence the name for the species.

Use. One source of potassium compounds which are exten sively used as fertilizers. Other potassium minerals that are found in Germany in sufficient amount to make them valuable as sources of potassium salts are, camallite, KCl.MgCl2.6H20 (see page 186); kainite, MgS04.IvC1.3H20; polyhalite, K2S04.MgS04.- 2CaS04.2H20.

Cerargyrite. Horn Silver

Composition. Silver chloride, AgCl Silver 75.3, chlorine 24.7. Somfvhrieties contain mercury.

Crystallization. Isometric. Habit cubic.

Structure. Usually massive, resembling wax; often in plates and crusfe. nfc

Physical Property. H. 2-3. G. 5.8-6. Sectile, can be cut with a knife like horn. Transparent to translucent. Color pearl-gray to colorless. Rapidly darkens to violet-brown on ex posure to light.

Tests. Very easily fusible at 1. B. B. on charcoal gives a globule of silver. Insoluble in nitric acid, but slowly soluble in ammonium hydroxide. When heated with galena in C. T. gives a white sublimate of lead chloride. Distinguished chiefly by its homy or waxlike appearance and its seetility.

Occurrence. Cerargyrite is an important secondary ore of silver. It is only to be found in the upper, enriched zone of silver veins where descending waters containing small amounts of chlorine have acted upon the oxidized products of the primary silver ores of the vein. Found associated with other silver ores, galena, etc.; with native sil ver, cerussite and secondary minerals in general. Was an important mineral in the mines at Leadville and elsewhere in Colorado, at the Comstock Lode in Nevada, in crystals at the Poorman's Lode in Idaho. Notable amounts have been found in New South Wales, Peru, Chile, Bolivia, and Mexico.

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Name. Cerargyrite is derived from two Greek words meaning horn and silver, in allusion to its hornlike appearance and char acteristics.

Use. Silver ore.

Embolite

Composition, Crystallization, structure and physical properties, like those of cerargyrite (which see). Tests, same as for cerargyrite, except that, when heated in C. T. with galena, it gives a lead bromide sublimate, which is yellow when hot and white when cold. Occurrence, same as for cerargyrite, with which it is usually found, but much rarer.

Other similar silver compounds which are still rarer in their oc currence are, bromyrite, AgBr; iodobromite, iodyrite, Agl.

Fluorite. Fluor Spar

Composition. Calcium fluoride, CaF2 Fluorine 48.9, cal cium 51.1.

Crystallization. Isometric. Habit cubic (Fig. 243) often in twinned cubes (Figs. 244 and 245). Other forms are rare, but examples of all the forms of the Normal Class have been observed; the tetrahexahedron (Fig. 246) and hexoctahedron (Fig. 247) are characteristic.

Structure. Usually crystallized. Also massive; coarse or fine granular, columnar.

Physical Properties. Perfect octahedral cleavage. H. =4. G. 3.18. Transparent to subtranslucent. Vitreous luster. Color widely various; most commonly light green, yellow, bluish green or purple, also colorless, white, rose, blue, brown. A single crystal may show varying bands of color; the massive variety is also often banded in color. The bluish green varieties often show fluorescence green by transmitted light, blue by reflected light) f Some varieties phosphoresce when heated, giving off variously

1 a

a

a

Fig. 243.

Fluorite

colored lights which are independent of the actual color of the specimen. The variety affording a green light is known as chlorophane.

Fig. 244.

Tests. Fusible at 3, and residue gives alkaline reaction to moistened test paper. Gives a reddish flame (calcium). When mixed with potassium bisulphate and heated in C. T., hydro fluoric acid is evolved which etches the glass, and a white deposit of silica forms upon the walls of the tube. Determined usually N by its cubic crystals and octahedral cleavage, also vitreous luster c / and usually fine coloring, and by the fact that it can be scratched y / with a knife.

Occurrence . A common and widely distributed mineral. Usually found either in veins in which it is the chief mineral or as a gangue mineral with metallic ores, especially those of lead and tin. Com mon in dolomites and limestone and has been observed also as a minor accessory mineral in various igneous rocks. Associated with

Manual Of Mineralogy

many different- minerals, as calcite, dolomite, gypsum, celestite, barite, quartz, galena, sphalerite, cassiterite, topaz, tourmaline, apatite.

The more important deposits in the United States are in southern Illinois near Rosiclare, and in the adjacent part of Kentucky. The fluorite occurs here in limestone, in fissure veins which at times be come 40 feet in width. Fluorite is found in quantity in England, chiefly from Cumberland, Derbyshire and Durham; the first two localities being famous for their magnificent crystallized specimens. Found commonly in the mines of Saxony. — Fine specimens come from Switzerland, the Tyrol, Bohemia.. Norway, etc.

Use. Fluorite is used mainly as a flux in the making of steel, in the manufacture of opalescent glass, in enameling cooking utensils, for the preparation of hydrofluoric acid, and occasionally as an ornamental material in the form of vases, dishes, etc.

Cryolite

Composition. A fluoride of sodium and aluminum, Na*AlF Fluorine 54.4, aluminum 12.8, sodium 32.8.

Crystallization. Monoclinic. Prominent forms are prism and base. Crystals rare, usually cubic in aspect, and in parallel groupings growing out of massive material.

Structure. Usually massive.

Physical Properties. H. 2.5. G. 2.95-3. Vitreous to greasy luster. Colorless to snow-white. Transparent to trans lucent. A low index of refraction, giving the mineral an appear ance of watery snow or of paraffin. Powdered mineral almost disappears when immersed in water.

Tests. Easily fusible (1.5), with strong yellow sodium flame. After intense ignition, residue gives alkaline reaction on moist ened test paper. Fused in C. T. with potassium bisulphate, evolves hydrofluoric acid and gives a volatile white ring of silica. Characterized by its massive structure, white color and peculiar luster.

Occurrence. Occurs in a large vein lying in granite at Arksukfiord on the west coast of Greenland. The following minerals are found in small amounts associated with the cryolite: quartz, siderite, galena, sphalerite, pyrite, chalcopyrite, wolframite, fluorite, cassit-

At Ac Amite

erite, molybdenite, arsenopyrite, columbite. Found also in very small amounts at Miask, Ilmen Mountains, Siberia, and at foot of Pike's Peak, Colorado.

Name. Name is derived from two Greek words meaning frost and stone, in allusion to its icy appearance.

Use. It is used for the manufacture of sodium salts, of certain kinds of glass and porcelain, and as a flux in the electrolytic process for the production of aluminum.

2. Oxychlorides, Etc.

Atacamite

Composition. Copper chloride with copper hydroxide, Chlorine 16.6, copper 14.9, cupric oxide 55.8, water 12.7.

Crystallization. Orthorhombic. Commonly slender pris matic in habit, with vertical striations. Also tabular parallel to brachypinacoid.

Structure. In confused crystalline aggregates; fibrous; gran ular. As sand.

Physical Properties. Cleavage perfect parallel to brachy pinacoid. H. 3-3.5. G. 3.75-3.77. Adamantine to vitre ous luster. Color various shades of green. Transparent to translucent.

Tests. Fusible (3-4), giving an azure-blue flame of copper chloride. B. B. on charcoal with sodium carbonate gives globule of copper. Nitric acid solution with silver nitrate gives white precipitate of silver chloride; with ammonia in excess gives blue solution. Gives acid water in C. T. Characterized by its green color and granular crystalline structure. Distinguished from malachite by its lack of effervescence in acids.

Occurrence. A comparatively rare copper mineral. Found originally as sand in the province of Atacama in Chile. Occurs with other copper ores in various localities in Chile and Bolivia. Found in some of the copper districts of South Australia; occurs sparingly in the copper districts of Arizona.

Use. A minor ore of copper.

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3. Hydrous Chlorides, Etc.

Carnallite

A hydrous chloride of potassium and magnesium, KCl.MgClj.- 6HjO- Orthorhombic. Massive, granular. Crystals rare. Lus ter nonmetallic, shining, greasy. Color milk-white, often reddish, due to included hematite. Transparent to translucent. H. 1. G. 1.6. Bitter taste. Deliquescent. Fusible at 1-1.5 with vio let flame. After ignition gives an alkaline reaction on moistened test paper. Easily and completely soluble in water; on addition of nitric acid and silver nitrate gives a white precipitate of silver chloride. Acid solution neutralized with ammonia and sodium phosphate added gives a white precipitate of ammonium magnesium phosphate. Found associated with halite, sylvite, etc., in the salt deposits at Stassfurt, Prussia. Used as a source of potassium compounds.

Oxides

The oxides are subdivided into three sections: (1) Oxides of Silicon; (2) Oxides of the Semimetals; (3) Oxides of the Metals.

1. Oxides Of Silicon

Quartz

Composition. Silicon dioxide, Si02 Oxygen 53.3, silicon 46.7. Often with various impurities.

Crystallization. Hexagonal-rhombohedral ; trapezohedral. Crystals commonly prismatic, with prism faces horizontally striated. Terminated usually by a combination of a positive and negative rhombohedron, which often are so equally devel oped as to give the effect of a hexagonal pyramid (Fig. 248). Sometimes one rhombohedron predominates or occurs alone (Fig. 249). At times the prism faces are wanting, and the com bination of the two rhombohedrons gives what appears to be a doubly terminated hexagonal pyramid (known as a quartzoid) (Fig. 250). Crystals at times very much distorted, when the recognition of the prism faces by their horizontal striations will assist in the orientation of the crystal. The trapezohedral faces are to be occasionally observed as small truncations between a

Quartz

prism face and that of an adjoining rhombohedron either to the right or left, forming what are known as right- or left-handed crystals (Figs. 251 and 252). Crystals are often elongated in tapering and sharply pointed forms, due to an oscillatory com bination between the faces of the different rhombohedrons and those of the prism (A, PI. VI). Sometimes twisted and bent.

Fig. 251. Right-handed Crystal. Fig. 252. Left-handed Crystal.

Crystals frequently twinned. The twins at times are so inti mately intergrown that they can only be determined by the ir regular position of the trapezohedral faces, by etching the crystal or by the pyroelectric phenomena that they show.

Structure. Commonly in crystals. From large crystals usually attached at one end, to finely crystalline coatings, forming "drusy" surfaces. Also common in massive forms of great variety. From coarse- to fine-grained crystalline to flintlike or cryptocrys talline varieties. Sometimes in concretionary forms, mammillary, etc. As sand.

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Physical Properties. H. 7. G. 2.65—2.66. Vitreous luster, sometimes greasy, splendent to nearly dull. Color widely various. Usually colorless or white, but frequently colored by various impurities, yellow, red, pink, amethyst, green, blue, brown, black. Transparent to opaque. Conchoidal fracture.

Tests. Infusible. Insoluble. Yields a clear glass when the finely powdered mineral is fused with an equal volume of sodium carbonate. Usually told by its glassy luster, conchoidal fracture, hardness (7) and crystal form.

Varieties. A great many different forms of quartz exist to which varietal names have been given. The more important varieties with a brief description of each follow.

A. Crystalline Varieties

1. Rock Crystal. Colorless quartz, commonly in distinct crystals.

2. Amethyst. Quartz colored purple or violet, often crystallized.

3. Rose Quartz. Usually massive, color a rose-red or pink. Often fades somewhat on exposure to light.

4. Smoky Quartz; Cairngorm Stone. Crystallized quartz of a smoky yellow to brown and almost black color. Named cairn gorm from the locality of Cairngorm in Scotland.

5. Citrine. Light yellow in color.

6. Milky Quartz. Milky white in color and nearly opaque. Sometimes with greasy luster.

7. Cat's-eye. A stone, which when cut in a round shape (en cabochon) exhibits an opalescent or chatoyant effect, as it is termed, is called a cat's-eye. Quartz among other minerals gives at times this effect, which is due either to fibrous inclusions or to a fibrous structure of the quartz itself. The latter is seen in the tiger's-eye, a yellow fibrous quartz from South Africa, which is pseudomorphic after another fibrous mineral, crocidolite.

8. With Inclusions. Many other minerals occur at times as inclusions in quartz. Rutilated quartz has fine needles of rutile penetrating it. Tourmaline and other minerals are found in quartz in the same way. Aventurine is quartz including brilliant

Plate Vi.

A. Smoky Quartz, Pike's Peak, Colorado.

B. Agate, Oberstein, Germany.

Quartz

scales of hematite or mica. Liquids and gases at times occur as inclusions; both liquid and gaseous carbon dioxide exist in some quartz.

Varieties

1. Chalcedony. An amorphous quartz material, translucent with a waxy luster. White, yellowish brown to dark-brown in color. Often mammillary, stalactitic, etc., in structure. De posited from aqueous solutions and found lining or filling cavities in rocks (see Fig. B, pi. III).

2. Camelian. A red chalcedony.

3. Chrysoprase. An apple-green chalcedony.

4. Heliotrope or bloodstone. A green chalcedony with small red spots in it.

5. Agate. A variegated chalcedony. The different colors usually in delicate, fine parallel bands which are commonly curved, sometimes concentric (Fig. B, pi. VI). The color is sometimes strengthened or even changed by artificial means. Some agates have the different colors arranged not in bands but irregularly distributed. Moss agate is a variety in which the variation in color is due to visible impurities, often manganese oxide.

6. Onyx. A banded chalcedony like agate, except the bands are arranged in straight parallel lines.

7. Flint. Something like chalcedony but of dull, often dark color. It breaks with a prominent conchoidal fracture and gives a sharp edge. Used for various implements by early man.

8. Jasper. Opaque quartz, usually colored red from hematite inclusions.

Occurrence. From the result of thermal studies it has been shown that quartz exists in two modifications, called a- and /3-quartz, which differ from each other slightly in crystal symmetry, refractive indices, etc. a-quartz is formed at temperatures below 575° C. and occurs in veins, geodes, and large pegmatites, while /3-quartz is formed between 575° and 870° C. and is characteristic of graphic granite, pegmatites, and porphyries. Above 870° the polymer known as tridymite is formed and above 1470° that known as cristobalite. Quartz is the most common of minerals. It has been estimated that quartz forms about twelve per cent of the minerals constituting the

Manual Of Mineralogy

rocks of the earth's crust. Occurs as an important constituent of the acid igneous rocks, such as granite, rhyolite, pegmatite, etc. It is a common mineral of sedimentary rocks, forming the chief mineral in sandstone. Occurs largely also in metamorphic rocks, as gneisses and schists, while it forms practically the only mineral of quartzites. Deposited often from solution and forms the most common vein and gangue mineral. In rocks it is associated chiefly with feldspar and muscovite; in veins with practically the entire range of vein minerals. Often carries gold and becomes an important ore of that metal. Occurs in large amount as sand in stream beds and upon the seashore and as a constituent of soils.

Rock crystal is found widely distributed, some of the more notable localities being: the Alps; Minas Geraes, Brazil; on the island of Madagascar; in Japan. The best quartz crystals from the United States are found at Hot Springs, Arkansas; and Little Falls and Ellen ville, New York. Important occurrences of amethyst are located in the Ural Mountains, Czechoslovakia, Tyrol, and in Brazil. Found at Thunder Bay on the north shore of Lake Superior; and in the United States in Delaware and Chester counties, Pennsylvania; Black Hills, South Dakota, Wyoming, etc. Smoky quartz is found in large and fine crystals in Switzerland; at Pike's Peak, Colorado- Alexander County, North Carolina; at Auburn, Maine, etc. The chief source of agates at present is a district in southern Brazil and northern Uruguay. They are mostly cut at Oberstein, Germany, itself a famous agate locality. Found in Laramie County, Wyoming, and numerous other places in the United States. Massive quartz, occurring in quartz veins or with feldspar in pegmatite veins, is mined for its various commercial uses in Connecticut, New York, Maryland, Wisconsin, etc.

Use. Widely used in its various colored forms as ornamental material, as amethyst, rose quartz, cairngorm, cat's-eye, tiger's- eye, aventurine, carnelian, agate, onyx, etc. Used for abrading purposes either as quartz sand or as sandpaper. Used in the manufacture of porcelain, of glass, as a wood filler, in paints, scouring soaps, etc. As sand is used in mortars and cements. As quartzite, sandstone, and in its various other rock forms as a building stone, for paving purposes, etc. Large amounts of quartz sand are used as an acid flux in certain smelting operations.

Opal

Composition. Silicon dioxide, like quartz, with a varying amount of water, Si02nH20. A mineral-gel.

Opal

Crystallization. Amorphous.

Structure. Massive.: often hotrvoidal. stalactitic. etc.

Physical Properties. H. 5. 5-6. 5. G. 1.9-2. 3. Vitre ous luster; often somewhat resinous. Colorless, white, pale shades of yellow, red, brown, green, gray and blue. With darker colors, which are due to various impurities. Often has a milky or "opal escent" effect and sometimes shows a fine play of colors. Trans parent to opaque.

Tests. Infusible. Insoluble. Reacts like quartz. Gives a little water upon intense ignition in C. T.

Varieties. Precious Opal. White, milky blue, yellow. Some times dark, as in so-called black opal. Translucent, with an inter nal play of colors. This phenomenon is said to be due to thin curved laminae which refract the light differently from the mass of the material, and so serve to break it up into the various prismatic colors. Fire opal is a variety with intense orange to red reflections.

Common Opal. Milk-white, yellow, green, red, etc., without internal reflections.

Hyalite. Clear and colorless opal with a globular or botryoidal structure.

Geyserite. Opal deposited by hot springs and geysers. Found about the geysers in the Yellowstone Park.

Wood Opal. Fossil wood with opal as the petrifying material.

Tripolile, or Inf usorial earth. Fine-grained deposits, resembling chalk in appearance. Formed by the accumulation of the siliceous shells of small sea organisms.

Occurrence. Opal is found lining and filling cavities in igneous and sedimentary rocks, where it has evidently been deposited through the agency of hot waters. Deposited from hot springs and occurs in sedimentary beds due to the accumulation of siliceous skeletons of minute sea animals. In its ordinary variety it is of widespread occurrence. Precious opals are found at Czernowitza, Hungary; in Queretaro and other states in Mexico; in Honduras; and from various localities in Australia, the chief district being White Cliffs, New South Wales. Recently black opal has been found in Nevada jyidldaho.

Use. As a gem. The stones are usually cut in round shapes, en cabochon. Stones of large size and exceptional quality are very highly prized.

Manual Of Mineralogy

2. Oxides Of The Semimetals

The minerals of this division are all rare in occurrence. Some of the more important species are, arsenolite, As203; senarmontile, Sb203 ; valentinite, Sb203; tellurite, Te02; tungstite, W03; cervantite, Sb204.

3. Oxides Of The Metals

The oxides of the metals are grouped into two main divisions: A. Anhydrous Oxides; B. Hydrous Oxides. Further, the Anhy drous Oxides are further subdivided into: (1) Protoxides; (2) Sesquioxides; (3) Intermediate Oxides; (4) Dioxides.

A. Anhydrous Oxides 1. Protoxides

Cuprite. Ruby Copper. Red Copper Ore

Composition. Cuprous oxide, Cu20 Oxygen 11.2, copper

Crystallization. Isometric. Common forms are cube, octa hedron and dodecahedron, frequently in combination (Fig. 253).

Sometimes in much elongated cubic crystals, capillary in size; known as "plush copper" or chalcotrichite.

Structure. Usually massive, more rarely in crystals or capillary fonns.

Physical Properties. H. =3.5-4. G. =6. Luster adamantine hi clear crystallized va rieties to submetallic and earthy in massive varieties. Color red of various shades. Ruby-red in transparent crystals. Streak brownish red. Indian-red. High index of re fraction, giving brilliant luster to transparent variety.

Tests. Easily fusible at 3, giving emerald-green flame, or, if moistened with hydrochloric acid and then heated, flame is azure-blue. Gives globule of copper on charcoal in R. F. When dissolved in small amount of concentrated hydrochloric acid and solution diluted with cold water gives a white precipitate of cuprous

Zincite

chloride (test for cuprous copper). Usually to be determined by its color and streak.

Occurrence. An important ore of copper of secondary origin. Found in the upper, oxidized portions of copper veins, associated with the other secondary copper minerals, native copper, malachite, azurite, chrysocolla, etc. Found in the United States in connection with the copper deposits at Bisbee, Morenci, etc.. Arizona. An im portant ore in Chile, Bolivia!, South Australia, New South Wales, French Congo, etc. Fine crystals come from Bisbee, Arizona; Cornwall, England; Chessy, France; the Urals.

Name. Derived from the Latin, cuprum, copper.

Use. Ore of copper.

Zincite

Composition. Zinc oxide, ZnO Oxygen 19.7, zinc 80.3. Manganese protoxide often present.

Crystallization. Hexagonal ; hemimorphic. Terminated above by faces of a steep pyramid and below with a basal plane. Sometimes shows short prism.

Structure. Usually massive with platy or granular structure.

Physical Properties. Perfect nasal cleavage. H. 4-4.5. G. 5.5. Luster subadamantine. Color deep red to orangeyellow. Streak orange-vellow. . Translucent to almost opaque.

Tests. Infusible. Soluble in hydrochloric acid. When the finely powdered mineral is mixed with sodium carbonate and charcoal dust and intensely heated B. B., gives a nonvolatile coating of zinc oxide, yellow when hot, white when cold. Usually with borax bead in O. F. gives a reddish violet color (manganese). Told chiefly by its color and streak.

Occurrence. Found in the zinc deposits at Brant-[jp .ce., New Jersey, associated with franklinite and willemite, often in an intimate mixture. Sometimes embedded in pink calcite. Reported in small amounts from various other localities.

Use. An ore of zinc, particularly used for the production of zinc white (zinc oxide).

In this division also belong water, ice, 11,0, which is huuronal in /crystallization, and tenorite or melaconite, CuO.

Manual Of Mineralogy

2. Sesquioxides Hematite Group

The Hematite Group includes the closely related rhombohedral minerals, corundum, A1203, hematite, Fe203, and ilmenite

Corundum

Composition. Aluminum oxide, A1203 Oxygen 47.1, alu minum 52.9.

Crystallization. Hexagonal-rhombohedral. Crystals usually prismatic in habit or tapering hexagonal pyramids (Figs. 254 and 255). Often rounded into barrel shapes (Fig. 256). Frequently with deep horizontal striations. At tunes shows rhombohedral and pyramidal faces.

Fig. 256.

Fig. 255.

Fig. 254.

Structure. Rudely crystallized or massive with parting planes nearly cubic in angle; coarse or fine granular.

Physical Properties. Parting basal and rhombohedral, the latter giving nearly cubic blocks. H. 9 (next to the diamond in hardness). G. 3.95-4.1 (unusually high for a nonmetallic mineral). Adamantine to vitreous luster. Color various. Usu ally some shade of brown, pink or blue. May be white, gray, green, ruby-red or sapphire-blue. Transparent to opaque.

Tests. Infusible. Insoluble. Finely pulverized material moistened with cobalt nitrate and intensely ignited aasumes a

Corundum

blue color (aluminum). Characterized chiefly by its great hard ness, adamantine luster and high specific gravity.

Varieties. Ordinary Corundum. In translucent to opaque masses, showing often the nearly cubical parting; also granular to compact.

Gem Corundum. When transparent and finely colored, corun dum furnishes various gem stones. The ruby is deep red corun dum ; sapphire is blue corundum. Stones of other colors are sometunes spoken of as yellow, violet, etc., sapphires, or are designated by prefixing the word oriental to the name of some other mineral similar in color; thus, oriental topaz, is a brownish yellow corun dum; oriental amethyst, a reddish violet corundum, etc.

Emery. Is a fine-grained corundum mixed with other minerals,

Occurrence. Common as an accessory mineral in the metamorphic rocks, such as crystalline limestone, mica-schist, gneiss, etc. Found also as an original constituent of certain igneous rocks, usually those deficient in silica. Found sometimes in large masses, evidently the product of magmatic differentiation. Found frequently in crys tals and rolled pebbles in detrital soil and stream sands, where it has been preserved through its hardness. Associated minerals are com monly chlorite micas, chrysolite, serpentine, magnetite, spinel, cyanite, diaspore, etc.

Rubies are found chiefly in Siam and Ceylon. The most important locality in Burmah is near Mogok, 90 miles north of Mandalay. The stones are found here chiefly in the soil resulting from the decay of a metamorphosed limestone. They have also been found in situ in the limestone. The rubies of Siam are found near Bangkok, on the Gulf of Siam, where they occur in a clay, derived from the decomposition of a basalt. The rubies of Ceylon are found with other gem stones in the stream gravels. A few rubies have been found in the gravels and in connection with the larger corundum deposits of North Carolina.

Sapphires are found associated with the rubies of Siam and Cey lon. They occur also in Kashmir, India. In the United States small sapphires of fine color are found in various localities in Montana. They were first found in the river sands east of Helena when washing them for gold. They have since been found embedded in the rock of lamprophyre dikes. The rock is quarried and after exposure to the air for a time it gradually decomposes, setting the sapphires free. Sapphires are also found over an extensive area in central Queens land, Australia.

Manual Of Mineralogy

Massive corundum is found in the United States in various locali ties along the eastern edge of the Appalachian Mountains from North Carolina south. It has been extensively mined in southwest ern N orth .jarohna. It occurs here in large masses lying at the edges of intruded masses of a chrysolite rock (dunite) and is thought to have been a separation from the original magma. Found as an original constituent of a nepheline syenite in the Province of Ontario. Canada. At times the corundum is so abundant as to form more than 10 per cent of the rock mass.

The impure corundum, known as emery, is found in large quanti ties on Cape Emeri on the island of Naxos and in various localities in Asia Minor. In the United States emery has been extensively

mined at Chester, Massachusetts.

Artificial. Artificial corundum is now being made in the elec trical furnaces at Niagara. Synthetic rubies and sapphires, colored with minute amounts of chromium, are made in consider able amount and in many cases it is difficult to distinguish them when cut from the natural occurring stones. Also small grains of the natural stone have been fused together into larger masses, from which stones of two or three carats in size can be cut. These are known as reconstructed rubies and sapphires.

Use. As a gem stone. The ruby at times yields the most valuable of gems; a stone of the deep red known as "pigeon's blood" may bring large amounts. The blue sapphire is also valuable, and stones of other colors may command good prices.

Used also as an abrasive, either ground from the pure massive material, or in its impure form as emery. Artificial corundum _and carborundum, which in composition is a carbide of silicon, are now, manufactured on a large scale in electric furnaces and are being used in considerable amount as abrasives instead of the naturally occurring corundum.

Hematite

Composition. Iron sesquioxide, Fe203 Oxygen 30, iron 70. Sometimes with titanium and magnesium, passing into ilmenite.

Crystallization. Unxant-in 1-rhoin I xihedral . Crystals usually thick to thin tabular Basal pThrii's 'prominent, often showing triangular markings (Figs. 257 and 258). Edges of plates some-

Hematite

times beveled with rhombohedral and pyramidal forms (Fig. 259). Thin plates at times grouped in rosette forms (iron roses) (Fig. 260). More rarely crystals are distinctly rhombohedral, often with nearly cubic angles.

Fig. 257.

Fig. 258.

Structure. Usually earthy or in botryoidal to reniform shapes with radiating structure. At times micaceous; crystallized.

Physical Properties. Rhombohedral parting with nearly cubic angles. H. 5.5-6. 5. G. 4.8-5.3. Metallic luster. Color reddish brown to black. Streak light to dark Indian-red.

Fig. 259.

Fig. 260.

Tests. Infusible. Becomes strongly magnetic on heating in R. F. Slowly soluble in hydrochloric acid; solution with potas sium ferrocyanide gives dark blue precipitate (test for ferric iron). Told chiefly by its characteristic Indian-red streak.

Varieties. Specular Hematite. Black hematite with brilliant, splendent luster (whence name, specular, mirrorlike), in crystals or in foliated masses with micaceous structure.

Columnar to Reniform Hematite, Kidney Ore. Brownish black color, in columnar to reniform shapes with radiating structure, having fibrous appearance (A, pi. III).

Oolitic and Fossil Ore. Impure hematite in small globular or lenticular concretions. At times with fossils.

Earthy Hematite. In pulverulent, earthy form of various shades of reddish brown. Often somewhat hydrated and passing into limonite.

Manual Of Mineralogy

Occurrence. Hematite is a widely distributed mineral in rocks of all ages and forms the most abundant ore of iron. It may occur as a sublimation product in connection with volcanic activities. Occurs as an accessory mineral in feldspathic igneous rocks, such as granite; at times it is of pneumatolytic origin. Found from microscopic scales to enormous masses in connection with metamorphic rocks where it may have originated by the alteration of limonite, siderite, magnetite, etc. Like limonite, it may be formed in irregular masses and beds as the result of the weathering of iron-bearing rocks. The oolitic ores are of sedimentary origin and may occur in beds of con siderable size. It is found in red sandstones as the cementing material that binds the quartz grains together.

The crystallized variety is found at many places, more particu larly from, the island of Elba; St. Gothard, Switzerland, in "iron roses"; in the lavas of Vesuvius; at Cleator Moor, Cumberland, etc. In the United States the columnar and earthy varieties are found in enormous beds that furnish a large proportion of the iron ore of the world. The chief iron-ore districts of the United States are grouped around the southern and northwestern shores fake Superior in Michigan, Wisconsin and Minnesota. The chief dis tricts, which are spoken of as iron-ore ranges, are, from east to west, the Marquette Range in northern Michigan; the Menominee Range in Michigan to the southwest of the Marquette; the Penokee- Gogebie Range in northern Wisconsin; the Mesabi Range, north of Duluth in Minnesota; and the Vermillion Range farther north in Minnesota, near the Canadian boundary. The iron ore of these different ranges varies from the hard black micaceous specular variety to the soft red earthy type. All of the ore bodies lie in rock troughs which furnish impervious underlying basements to the deposits. In all of the districts, except the Mesabi, these under lying rocks are in the nature of altered igneous dikes, known as soapstone dikes. The ore bodies lie in more or less broken quartz material, frequently colored red by inclusions of hematite and called jasper. The origin of these deposits is attributed to the slow con centration of the iron content of a siliceous carbonate rock by down ward moving waters. These waters were at last collected in the impervious rock troughs and there deposited their iron content by a replacement of the quartz of the overlying rock. The ores are mined in part by underground methods, and in part, where the ore is soft and lies sufficiently near the surface, by the use of steam shovels.

Hematite is also found in the United States in various places in connection with the outcrop of rocks of the Clinton formation, from central New York south along the line of the Appalachian Moun tains to central Alabama. The most important deposits of the series lie in eastern Tennessee and northern Alabama, near Birming-

Ilmen I Te

ham. Hematite has been found at Iron Mountain and Pilot Knob in southeastern Missouri. Deposits of considerable importance are 1 seated i n AVyrnu i n p- in Laramie and Carbon counties.

Name. Derived from a Greek word meaning blood, in allusion to the color of the powdered mineral.

Use. Most important ore of iron. In red pigments As

polishing powder, etc.

Ilmenite. Menaccanite. Titanic Iron Ore

Composition. Ferrous titanate, FeTi03 Oxygen 31.6, tita nium 31.6, iron 36.8. By the introduction of ferric oxide, the ratio between the titanium and iron often varies widely. Sometimes contains magnesium replacing the ferrous iron.

Crystallization. Hexagon;! ,1- boh o.i ) ml ; tri-rhombohedral. Crystals usually thickQabulahwlth prominent basal planes and small rhombohedral truncations. Faces of the third order rhombohedron rare. Crystal angles, etc., close to those for hematite.

Structure. Usually massive, compact; also in grains or as sand. Often in thin plates.

Physical Properties. H. 5.5-6. G. 4.7. Metallic to submetallic luster. Color iron-black. Streak black to brownish red. Sometimes magnetic without heating.

Tests. Infusible. May be magnetic without heating. Fine powder fused in R. F. with sodium carbonate yields a magnetic mass. After fusion with sodium carbonate the fusion can be dis solved in hydrochloric acid, and when the solution is boiled with tin it assumes a violet color (titanium).

Occurrence. Occurs as beds and lenticular bodies enveloped in gneiss and other crystalline metamorphic rocks. Frequently found in veins or large segregated masses near the borders of igneous rocks. Often associated with magnetite. Also as an accessory mineral in eruptive rocks. Found in large quantities at Kriigero and other localities in Norway; at Miask in the Ilmen Mountains; at, pap. St. Paul in Ouehec-JCanada. Found at Washington, Connecticut; in Orange County, New York, with many of the magnetite deposits of the Adirondack region.

Use. Has practically no commercial use. A little of it present in a body of magnetite iron ore makes the ore so difficult to smelt as to render it of little value.

Manual Of Mineralogy

3. Intermediate Oxides Spinel Group

A group of oxides which in composition are combinations of a bivalent oxide with a trivalent oxide, the general formula being, R"0.R*'"0. R"0 may be MgO, ZnO, FeO, MnO, while R/"Oj may be A1203, Fe203, Mn203, Cr203. The chief members of the group are as follows:

Spinel, Mg0.Al203 or MgAl204.

Gahnite, Zn0.Al203 or ZnAl204.

Magnetite, Fe0.Fe203 or FeFe204.

Franklinite, or (Fe,Mn,Zn)

Chromite, or

The crystalline habit of all the members of the group is octa hedral. The dodecahedron is sometimes present, but other forms are rare.

Spinel

Composition. MgAl204 or Mg0.Al203 Alumina 71.8, mag nesia 28.2. The magnesium may be, in part, replaced by ferrous iron or manganese and the aluminum by ferric iron and chromium.

Crystallization. Iscgebic. Habit strongly octahedral (Fig. 261). Some times in twinned octahedrons (spinel twins) (Fig. 262). Dodecahedron at times as small truncations (Fig. 263). Other forms rare.

Structure. TTsnfl.lly nrystallized. Physical Properties. II. G. 3.5-4. 1. Nonmetallic. Vitreous luster.

Fig. 281 Color various, — red, lavender, blue, green,

brown, black, sometimes almost white. Streak white. Usually translucent to opaque, at times clear and transparent.

Tests. Infusible. The finely powdered mineral dissolves completely B. B. in the salt of phosphorus bead (proving the

Spinel

absence of silica). Recognized chiefly by its hardness (8), its octahedral crystals and vitreous luster.

Varieties. 1. Ruby Spinel. Nearly pure magnesian spinel. Clear red; transparent to translucent. When rose-red known as bias ruby; yellow or orange-red, rubicelle; violet-red, almandine ruby.

Fig. 262.

Fig. 263.

2. Pleormste. Iron-magnesia spinel. Color dark green, brown to black. Opaque or nearly so.

3. Chlorospinel. Magnesia-iron spinel. Color grass-green ow ing to the presence of copper.

4. Picotite, or Chrome Spinel. Contains chromium and has iron replacing magnesium. Color yellowish or greenish brown. Translucent to opaque.

Occurrence. A common metamorphic mineral occurring embed ded in granular limestone, associated with calcite, serpentine, etc. Occurs also as an accessory mineral in many basic igneous rocks, as peridotites, etc. Spinel is frequently formed in contact zones be tween eruptive rocks and limestones, owing its origin to pneumatolytic conditions. Found frequently as rolled pebbles in stream sands, where it has been preserved on account of its hardness. The ruby spinels are found in this way, often associated with the corun dum ruby, in the sands of Ceylon. Siam, Upper Riinnah. Madagas car, etc. Ordinary spinel is found in various localities in New York, and New Jersey.

Use. When transparent and finely colored is used as a gem. Usually red in color and known as the spinel ruby, bias ruby, etc. Some stones are blue in color. The largest cut stone known

Manual Of Mineralogy

weighs in the neighborhood of 80 carats. The stones usually are comparatively inexpensive.

Gahnite

A zinc spinel, ZnAbCh or ZnO.Al203, with ferrous iron and man ganese isomorphous with the zinc and ferric iron with the aluminum. Isometric. Commonly octahedral, also rarely showing dodecahe drons and cubes. H. 7.5—8. G. 4.55. Vitreous luster. Dark green color. Infusible. The fine powder fused with sodium car bonate on charcoal gives a white nonvolatile coating of zinc oxide. A rare mineral. Found in the United States in notable crystals at Franklin, New Jersey, and Rowe, Massachusetts.

Magnetite

Composition. Fe304 or Fe0.Fe203 Iron sesquioxide 69.0, iron protoxide 31.0 or oxygen 27.6, iron 72.4. The ferrous iron is sometimes replaced by magnesium, rarely nickel; also at times titaniferous.

Crystallization. Igm-notric- Octa hedral habit (Fig. 264), sometimes twinned octahedrons. Dodecahedron at times (Fig.

265) either alone or with octahedron (Fig.

266) . Other forms rare.

Structure. Usually granular massive,

coarse or fine; sometimes as sand; also frequently crystallized.

Physical Properties. Often under pressure develops octahedral parting. , G. 5.18. Metallic luster. Color iron-black. Streak Strongly magnetic; sometimes a natural magnet, known as lodestone.

Tests. Infusible. Slowly soluble in HC1 and solution reacts for both ferrous and ferric iron. Distinguished chiefly by its strong magnetism, its black color and streak, and its hardness (6).

Occurrence. A common ore of iron. It is found as an accessory mineral in rocks of all classes and sometimes becomes their chief constituent. Most commonly associated with crystalline meta-

Franklinite

morphic rocks, also frequently in rocks that are rich in ferromagnesium minerals, such as diabase, gabbro, peridotite. In many cases forms large ore bodies that are thought to be the result of magmatic differentiation; such bodies are often highly titaniferous. Occurs at times in immense beds and lenses, inclosed in old metamorphic rocks. Found in the black sands of the seashore. Occurs as thin plates and dendritic growths between plates of mica. Often inti mately associated with corundum, forming the material known as emery.

Fig. 265. Fig. 266.

In the United States, found in large beds with the Archaean rocks of the Adirondacks in Warren, Essex and Clinton counties of north ern New York; in various places in New Jersey; at Cornwall, Penn sylvania. Important foreign localities are in Norway and Sweden, where it is the chief iron ore. Natural magnets or lodestones are found in Siberia; in the Harz Mountains, Germany; at Magnet Cove, Arkansas. " 1

Name. Probably derived from the locality Magnesia, border ing on Macedonia. A fable, told by Pliny, ascribes its name to a shepherd named Magnes, who first discovered the mineral on Mount Ida by noting that the nails of his shoes and the iron ferrule of his staff adhered to the ground.

Use. An important iron ore.

Franklinite

Composition. Shows wide vari ation in the proportions of the different elements present, but con forms to the general formula, R0.R203.

Manual Of Mineralogy

Crystallization. Isometric. —Habit strongly octahedral. Do decahedron sometimes as truncations. Other forms rare. Crys tals often rounded.

Structure. Massive, coarse or fine granular, in rounded grains or crystallized.

Physical Properties. H. =6. G. 5.15. Metallic luster. Color iron-black. Streak dark brown. Not magnetic.

Tests. Infusible. Becomes strongly magnetic on heating in R. F. Gives a bluish green color to sodium carbonate bead in 0. F. (manganese). When very fine powder is mixed with sodium carbonate and heated intensely on charcoal gives a coating of zinc oxide. Distinguished by above tests and its black color and brown streak.

Occurrence. Found practically only in the zinc deposits at Frank lin Furnace, New Jersey, which are in the form of large beds, inclosed in granular limestone. Associated chiefly with zincite and willemite, with which it is often intimately intergrown.

Use. As an ore of zinc and manganese. The zinc is converted into zinc white and the residue is smelted to form an alloy of iron and manganese, spiegeleisen, which is used in the manufacture of steel.

Chromite

Composition. FeCrA or FcO.CrA. Chromium sesqui oxide 68.0, iron protoxide 32.0. The iron may be replaced by magnesium and the chromium by aluminum and ferric iron.

Crystallization, jspmetric. Habit octahedral. Crystals small and rare.

Structure. Commonly massive, granular to compact.

Physical Properties. H. 5.5. G. 4.6. Metallic to submetallic luster. Color iron-black to brownish black. Streak, dark brown.

'''TesHn Infusible. When finely powdered and fused on char coal with sodium carbonate gives a magnetic residue. Imparts a green color to the borax and salt of phosphorus beads (chro mium).

Chrysoberyl

Occurrence. A common constituent of peridotite rocks and the serpentines derived from them. _One of the first minerals to separate from a cooling rock-magma, and its large ore deposits are thought to have been derived by such magmatic differentiation. Associated with chrysolite, serpentine, corundum, etc.

Found only sparingly in the United States. Pennsylvania, Mary land, North Carolina and Wyoming have produced it in the past. California is the only important producing state at present (1928). The important countries for its production are New Caledonia, Southern Rhodesia, Greece and Canada.

Uses. Chromium is used with various other metals to give hardness to steel. Chromite bricks are used to a considerable extent as linings for metallurgical furnaces, on account of their neutral and refractory character. The bricks are usually made of crude chromite and coal tar but sometimes of chromite with kaolin, bauxite, milk of lime or with other materials. Chromium is a constituent of certain green, yellow, orange and red pigments and of similarly colored dyes.

Chrysoberyl

Composition. Beryllium aluminate, Alumina 80.2, beryllium oxide 19.8.

Crystallization. Orthorhombic. Crystals usually tabular parallel to macropinacoid, which face is vertically striated. Com monly twinned, often in pseudohexagonal forms.

Structure. Usually in crystals.

Physical Properties. Prismatic cleavage. H. 8.5 (un usually high). G. 3.65-3.8. Vitreous luster. Color various shades of green, brown, yellow, sometimes red by transmitted light.

Tests. Infusible. Insoluble. The finely powdered mineral is wholly soluble in the salt of phosphorus bead (absence of silica). Mineral, moistened with cobalt nitrate and ignited, turns blue (aluminum). Characterized by its extreme hardness, its yellowish to emerald-green color and its twin crystals.

Varieties. 1. Ordinary. Color pale green, yellow; sometimes transparent.

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2. Alexandrite. Emerald-green variety, but red by transmitted light and generally also by artificial light.

3. Cat's-eye, or Cymophane. A variety which when polished shows an opalescent luster, and across whose surface plays a long narrow beam of light, changing its position with every movement of the stone. This effect is known as chatoyancy, and is best obtained when the stone is cut in an oval or round form (en cabochon). This property of the mineral is thought to be due to nu merous minute tubelike cavities, arranged in a parallel position. Chrysoberyl is the true cat's-eye, and is not to be confused with various other minerals possessing similar properties (e.g., quartz).

Occurrence. A rare mineral. Occurs in granitic rocks and peg matites and in mica schists. Frequently in river sands and gravels. Found in the alluvial gem deposits of Brazil and Ceylon; the alexan drite variety comes from the Ural Mountains. In the United States it has been found in Oxford Co., and elsewhere in Maine; Haddam, Connecticut; at Greenfield, near Saratoga, New York.

Name. Chrysoberyl means golden beryl. Cymophane is de rived from two Greek words meaning wave and to appear, in al lusion to the chatoyant effect of some of the stones. Alemrulrite was named in honor of Alexander II of Russia.

Use. Serves as a gem stone. The ordinary yellowish green stones are inexpensive, while the varieties alexandrite and cat's-eye are of considerable value.

Two rare manganese minerals belong in the section of Inter mediate Oxides: hausmannite, Mn0.Mn203, and braunite, 3Mn*0.- MnSi03.

4. Dioxides

Cassiterite. Tin Stone

Composition. Tin dioxide, Sn02 Oxygen 21.4, tin 78.6.

Crystallization. Tctragonab Common forms are prisms and pyramids of first and second orders (Fig. 267). Frequently in elbow-shaped twins; twinning plane being a pyramid of the second order (Fig. 268).

Cassiterite

Structure. Usually massive granular; often in reniform shapes with radiating fibrous-like structure ( wood tin ) ; crystallized.

Physical Properties. H. 6-7. G. 6.8-7. 1 (unusually high for a mineral with nonmetallic luster). Nonmetallic, ada mantine luster to submetallic and dull. Color usually brown or black; rarely yellow or white. Streak white.

Fig. 268.

Tests. Infusible. Gives globule of tin with coating of white tin oxide when finely powdered mineral is fused on charcoal with a mixture of sodium carbonate and charcoal powder. Insoluble. When fragments of cassiterite are placed in dilute hydrochloric acid together with a little metallic zinc the cassiterite becomes coated with a dull gray deposit of metallic zinc which becomes bright on friction. Recognized by its high specific gravity, its color and light streak.

Occurrence. Cassiterite is widely distributed in small amounts but is only produced on a commercial scale in a few localities. Gas~ siterite has been noted as an Qrjfrinf.1 PrmsttfciiPn.t..nf ignoni.9 rnr-l-a- but it is more commonly to be found in veins associated with quartz.

t y M hilo tin-hearing veins are found in or near pegmatites or granitic

rocks! Tin veins usually have minerals which contain fluorine and boron, such as tourmaline, topaz, fluorite, apatite, etc., and the min erals of the wall rocks are commonly much altered. It is thought, therefore, that the tin veins have been formed through the agency of vapors which carried tin with boron and fluorine. Cassiterite is at times a minor constituent of pegmatite veins. Also it is found in the form of rolled pebbles in placer deposits.

Cassiterite is not found in large quantities in the United States, the most important locality being on the Seward Peninsula, Alaska.

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Found also in the pegmatites of North and South Carolina; in the Black Hills, South Dakota. The world's supply of tin ore comes from from New South Wales, Queensland and other states of from Bolivia and from the Malay States. Cornwall England, has produced large amounts of tin ore in the past.

Use. Only ore of Jin. Chief use of tin is in coating or "tin ning" meals, particularly iron, to form what is known as sheet tin. Tin is also used in various alloys: solder, containing tin and lead; bell-metal and bronze, containing copper and tin.

Rutile

Composition. Titanium dioxide, Ti02 Oxygen 40, titanium 60. A little iron is usually present and may amount to 10 per cent.

Crystallization. Tetragonal. Usually prismatic with pyra mid terminations (Fig. Vertically striated. Frequently

Fig. 271.

in elbow twins, often repeated (Figs. 270 and 271). Twinning plane is pyramid of second order. Crystals sometimes slender acicular.

Structure. Usually crystallized. Sometimes compact mas sive.

Brookite

Physical Properties. H. ,6-0.5. G. 4.18-4.25. Luster adamantine to submetallic. Color red, reddish brown to black. Usually nearly opaque, may be transparent.

Tests. Infusible. Insoluble. Fused with sodium carbonate, then fused mass dissolved in hydrochloric acid and boiled with tin, the solution assumes a violet color.

Occurrence. Rutile is found in granite, gneiss, mica schist, metamorphic limestone and dolomite, sometimes as an accessory mineral in the rock, sometimes in quartz veins traversing it. Often occurs as slender crystals penetrating quartz. Remarkable crystals come from Graves Mountain, Lincoln County, Georgia. Also found in Alexander County, North Carolina, and at Magnet Cove Arkansas. Has been mined in Amherst and Nelson Counlies, Virginia. " Notable European localities are Kragero, Norway; Yrieix, near Limoges, France; in Switzerland and the Tyrol

Use. Source of titanium. Titanium is used to a small extent in steel and cast iron; for electrodes in arc lights; to give a yellow color to porcelain and false teeth.

Octahedrite. Anatase

Titanium dioxide, Ti02, same as rutile and brookite. Tetragonal. Usually in pyramidal crystals, also tabular parallel to base. H. 5.5-6. G. 3.8-3.95. Adamantine luster. Color yellow, brown, blue, black, transparent to opaque. Tests same as for rutile (which see). A comparatively rare mineral, found usually as an accessory mineral in metamorphic rocks, of secondary origin, having been derived from the alteration of other titanium-bearing minerals.

Brookite

Tilanium dioxide, Ti02, like rutile and octahedrite. Orthorhom bic. Habit varied. Tabular parallel to macropinacoid, square prismatic and at times by an equal development of 4 prism and 8 pyramid faces resembles a hexagonal pyramid. Occurs only in crys tals. H. =6. G. 4-4.07. Luster adamantine to submetallic.

Color hair-brown to black. Translucent to opaque. Tests, same as for rutile. A rare mineral, with mode of origin and associations similar to those of octahedrite. It is apparently formed at a tem perature which is lower than the formation temperature of rutile but higher than that of octahedrite. Occurs in good crystals at St.

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Gothard, etc., in Switzerland; in the Tyrol; Tremadoc, Wales; Ellenville, New York; Magnet Cove, Arkansas.

Pyrolusite

Composition. Manganese dioxide, MnOj. Commonly con tains a little water.

Crystallization. Crystals probably always pseudomorphous after manganite.

Structure. Radiating columnar to fibrous (Fig. A, pi. VII); also granular massive; often in reniform coats.

Physical Properties. H. 2-2.5 (often soiling the fingers). G. 4.75. Metallic luster. Iron-black color and streak. Splin tery fracture.

Tests. Infusible. A small amount of powdered mineral gives in 0. F. a reddish violet bead with borax or a bluish green opaque bead with sodium carbonate. Gives oxygen in C. T., which will cause a splinter of charcoal to ignite when placed in tube above the mineral and heated. Only a small amount of water in C. T. In hydrochloric acid, chlorine gas evolved.

Occurrence. A secondary mineral. Manganese is dissolved out of the crystalline rocks, in which it is almost always present in small amounts, and redeposited under various conditions, chiefly as pyro lusite. Dendritic coatings of pyrolusite are frequently observed on rock surfaces, coating pebbles, etc. Nodular deposits of pyro lusite are found on the sea bottom. Nests and beds of manganese ores are found inclosed in residual clays, derived from the decay of manganiferous limestones. It is thought that the manganese oxides were originally colloidal in character, having subsequent to deposition assumed a crystalline form. Also found in veins with quartz and various metallic minerals.

Pyrolusite is a common mineral, widespread in its occurrence. Mined in Thuringia, Moravia, Transylvania, Bohemia, West phalia, Australia, Japan, India, Brazil, New Brunswick, Nova. Scotia. In the United States, manganese ores are found in Virginia, Georgia, with the hematite ores of the Lake Superior districts, in Arkansas and California.

Name. Pyrolusite is derived from two Greek words meaning fire and to wash, because it is used to free glass through its oxidizing effect of the colors due to iron.

Plate Vii.

A. Pyrolusite, Negaunee, Michigan.

IS. Manganite, Ilefeld, Harz Mts.

Dias Pore

Uses. Most important manganese ore. Manganese is used in the manufacture of the alloys with iron , spiegeleisen and ferro manganese, employed in making steel; also in various alloys with copper, zinc, aluminum, tin, lead, etc. Pyrolusite is used as an oxidizer in the manufacture of chlorine, bromine and oxygen; as a disinfectant in potassium permanganate; as a drier in paints, a decolorizer of glass, and in electric cells and batteries. Manganese is also used as a coloring material in bricks, pottery, glass, etc.

Polianite, Mn02, is a rare mineral, occurring in minute tetragonal crystals.

B. Hydrous Oxides

Turgite. Hydrohematite

Composition is or 2Fe203.lH20. Compare limonite and goethite. Ren i form and stalactitic, with radiating fibrous structure. Sometimes earthy. H. 5.5-6. G. 4.14. Submetallic luster. Color black to reddish black. Streak Indian-red. Difficultly fusible at 5-5.5. Strongly magnetic after heating in R. F. In C. T. gives 5 per cent of water and generally decrepitates. Dis tinguished from limonite by red streak and from hematite by giving water in C. T. Found usually associated with limonite. Occurred in considerable amount at Salisbury, Conn., where it often formed an outer layer an inch or more in thickness on the masses of limonite.

Diaspore

Composition. or A1203.H20 Alumina 85, water

Crystallization. Orthorhombic. Usually in thin crystals, tabular parallel to the brachypinacoid.

Structure. Bladed; foliated massive.

Physical Properties. Perfect cleavage parallel to brachy pinacoid. H. 6.5-7. G. 3.35-3.45. Vitreous luster except on cleavage face, where it is pearly. Color white, gray, yellowish, greenish.

Tests. Infusible. Insoluble. Fine powder wholly soluble in salt of phosphorus bead (absence of silica). Ignited with cobalt nitrate turns blue (aluminum). Gives water in C. T. Character ized by its good cleavage, scaly structure and its hardness (6.5-7).

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Occurrence. Usually a decomposition product of corundum and found associated with that mineral in dolomite, chlorite-schist, etc. Occurs similarly in bauxite deposits. Has been noted as an accessory mineral in metamorphic limestones. Found in the Urals; at Schemnitz, Czechoslovakia; Campolungo in Switzerland. In the United States in Chester County, Pennsylvania; at Chester, Massachusetts; with alunite forming rock masses at Mt. Robinson, Rosita Hills, Colorado.

Name. Derived from a Greek word meaning to scatter, in al lusion to its decrepitation when heated.

Goethite

Composition. or Fe203.H20 Oxygen 26, iron 62.9, water 10.1.

Crystallization. Orthorhombic. Prismatic, vertically stri ated. Often flattened parallel to brachypinacoid. In acicular crystals at times.

Structure. Massive, reniform, stalactitic, with radiating fibrous structure. Foliated. Rarely in distinct crystals.

Physical Properties. Perfect cleavage parallel to brachy pinacoid. H. 5-5.5. G. 4.37. Adamantine to dull luster. Silky luster in certain fine scaly or fibrous varieties. Color yel lowish brown to dark brown. Streak yellowish brown (same as for limonite).

Tests. Difficultly fusible (5-5.5). Becomes magnetic in R. F. Water in C. T. Told chiefly by the color of its streak and dis tinguished from limonite by its tendency to crystallize and the smaller amount of water which it contains.

Occurrence. Occurs with the other oxides of iron, hematite and limonite. Also found in quartz as an alteration product of a sulphide. Found at Eiserfeld in Westphalia; from Pribram, Bohemia; at Lostwithiel, Cornwall. In the United States in connection with the Lake Superior hematite deposits, particularly at Negaunee, Michigan. In Colorado from Florissant, Teller Co., and in the Pike's Peak region.

Use. A minor ore of iron.

Limonite

Manganite

Composition. or Mn203.H20 Oxygen 27.3, manganese 62.4, water 10.3.

Crystallization. Orthorhombic. Crystals usually long pris matic with obtuse terminations, deeply striated vertically (Fig. B, pi. VII). Often twinned.

Structure. Usually in radiating masses; crystals often grouped in bundles. Also columnar.

Physical Properties. Perfect cleavage parallel to brachypinacoid. H. =4. G. 4.3. Metallic luster. Steel-gray to iron-black color. Dark brown streak.

Tests. Infusible. A small amount of the powdered mineral gives in 0. F. a reddish violet bead with borax or a bluish green opaque bead with sodium carbonate. Much water when heated in C. T. Told chiefly by its black color, prismatic crystals, hard ness (4) and brown streak. The last two will serve to distinguish it from pyrolusite.

Occurrence. Found associated with other manganese oxides and has a similar origin. It frequently alters to pyrolusite. Found often in veins associated with the acid igneous rocks, both as filling cavities and as a replacement of the neighboring rocks. Barite and calcite are frequent associates. Occurs at Ufeld, Harz Mountains, in fine crystals; also at Ilmenau, Thuringia; Cornwall, England; Negaunee, Michigan, etc. In Nova Scotia.

Use. A minor ore of manganese.

Limonite. Brown Hematite. Bog-iron Ore

Composition. or 2Fe203.3H20 Oxygen 25.7, iron 59.8, water 14.5. Often impure. Compare turgite and goethite. The water content of limonite varies widely and it is probable that the mineral is essentially an amorphous form of goethite with adsorbed and capillary water.

Crystallization.

Structure. In mammillary to stalactitic forms with radiating fibrous structure (Fig. B, pi. II); also concretionary; sometimes earthy.

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Physical Properties. H. 5-5.5. G. 3.6-6. Submetallic luster. Color dark brown to nearly black. Streak yellowish brown.

Tests. Difficultly fusible (5-5.5). Strongly magnetic after heating in R. F. Much water in C. T. (15 per cent). Charac terized chiefly by its structure and yellow-brown streak.

Occurrence. Limonite is a common ore of iron and is always secondary in its origin, formed through the alteration or solution of previously existing iron minerals. Pyrite is often found altered to limonite, the crystal form being at times preserved, giving limonite pseudomorphs. Sulphide veins are often capped near* the surface, where oxidation has taken place, by a mass of cellular limonite, which is known as gossan, or an iron hat. Iron minerals existing in the rocks are among the first to undergo decomposition, and their iron content is often dissolved by percolating waters through the agency of the small amounts of carbonic acid which they contain. The iron is transported as a carbonate by the waters to the surface and then often carried by the streams finally into marshes and stagnant pools. There, under the effect of the evaporation of the water and its consequent loss of the carbonic acid, which served to keep the iron carbonate in solution, and through the agency of the reducing action of carbonaceous matter present, the iron carbonate is changed to an oxide, which separates from the water and collects first as an iridescent scum on the surface of the water, and then later sinks to the bottom. This separation is also aided by the so-called "iron bacteria" which absorb the iron from the water and later deposit it again as ferric hydroxide. In this way, under favorable conditions, beds of impure limonite can be formed in the bottom of marshes and bogs. Such deposits are very common and are known as bog-iron ores, but, because of the foreign materials deposited along with the limonite, are seldom of sufficient purity to be worked.

Limonite deposits are also to be found in connection with iron bearing limestones. The iron content of the limestone is gradually dissolved by circulating waters and transported by them to some favorable spot, and there the iron is slowly redeposited as limonite, gradually replacing the calcium carbonate of the rock. Or, by the gradual weathering and solution of the limestone, its iron content may be left in the form of residual masses of limonite, lying in clay above the limestone formation.

Such deposits are often of considerable size, and because of their greater purity are much more often mined than the bog-iron ores. Deposits of this type are to be found chiefly along the Appalachian Mountains, from western Massachusetts as far south as Alabama.

Bauxite

These ores have been of considerable importance in western Massa chusetts, northwestern Connecticut, southeastern New York, and in New Jersey. They have also been mined in Alabama, Virginia, Tennessee and Georgia. Limonite deposits of various kinds are found throughout the western country, but as yet they have not been extensively developed. Oolitic limonites or "minettes" occur in large quantities in Lorraine and Luxemburg and constitute the most important iron ore deposits of Europe.

Limonite is the coloring material of yellow clays and soils, and mixed with fine clay makes what is known as yellow ocher. Limo nite is commonly associated in its occurrence with hematite, turgite, pyrolusite, calcite, siderite, etc.

Name. Derived from the Greek word meaning meadow , in allusion to its occurrence in bogs.

Use. As an iron ore. As a pigment, in yellow ocher.

Bauxite

Composition. or AI2O3.2H2O Alumina 73.9, water 26.1. Often impure.

Crystallization. Noncrystalline.

Structure. In round concretionary grains; also massive, earthy, claylike.

Physical Properties. G. 2-2.55. Dull to earthy luster. Color white, gray, yellow, red.

Tests. Infusible. Insoluble. Assumes a blue color when moistened with cobalt nitrate and then ignited (aluminum). Gives water in C. T.

Occurrence. A mineral of secondary origin, commonly produced under tropical climatic conditions by the prolonged weathering of aluminum-bearing rocks. Also at times derived from the weathering of clay-bearing limestones. It has apparently originated as a col loidal precipitate. It may occur in place as a direct derivative of the original rock or it may have been transported and deposited in a sedimentary formation. In the tropics, deposits, known as laterites, consisting largely of aluminum and ferric oxides are found in the residual soils. These vary widely in composition and purity but may at times become valuable as sources of aluminum and iron. Occurs over a large area in the south of France an important district being at Baux, near Arles, France. In the United States the chief deposits are found in Georgia, Alabama and Arkansas.

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Use. As an ore of aluminum, in the manufacture of aluminum salts; artificial abrasives and bauxite brick.

Brucite

Composition. Magnesium hydroxide, Magnesia 69.0, water 31.0. Iron and manganese sometimes present.

Crystallization. Hexagonal-rhombohedral. Crystals usu ally tabular with prominent basal planes, showing at times small rhombohedral truncations.

Structure. Commonly foliated, massive.

Physical Properties. Perfect basal cleavage. Folia flexible but not elastic. Sectile. H. 2.5. G. 2.39. Luster on base pearly, elsewhere vitreous to waxy. Color white, gray, light green. Transparent to translucent.

Tests. Infusible. B. B. glows. Gives water in C. T. Easily soluble in hydrochloric acid, and after solution has been made ammoniacal an addition of sodium phosphate gives a white granular precipitate of ammonium magnesium phosphate (test for mag nesium). Recognized by its foliated structure, light color and pearly luster on cleavage face. Distinguished from talc by its greater hardness and lack of greasy feel.

Occurrence. Found associated with serpentine, dolomite, mag nesite, chromite, etc., as a decomposition product of magnesium silicates. Notable localities for its occurrence are at Unst, one of the Shetland Islands; Aosta, Italy; at Tilly Foster Iron Mine, Brewster, New York; at Wood's Mine, Texas, Pennsylvania.

Gibbsite. Hydrargillite

Aluminum hydroxide, Monoclinic. Rarely in hexagonal-shaped tabular crystals. Stalactitic or botryoidal. Basal cleavage. H. 2-3.5. G. 2. 3-2.4. Luster pearly, vitreous or dull. Color white. Infusible. Insoluble in hydrochloric acid. Moistened with cobalt nitrate and ignited assumes a blue color. Water in C. T. A rare species of secondary origin resulting from the alteration of other aluminum bearing minerals, especially the silicates. Often associated with bauxite and a constituent of many laterites.

Calcite

Psilomelane

Of uncertain composition, chiefly manganese oxides, Mn02 with MnO and H20, also small amounts of barium oxide, cobalt oxide, etc. Noncrystalline. Massive, botryoidal, stalactitic. H. 5-6. G. 3.7— 4.7. Submetallic luster. Black color. Brownish black streak. Infusible. A small amount of mineral fused in O. F. with sodium carbonate gives an opaque bluish green bead. Gives much water in C. T. Distinguished from the other manganese oxides by its greater hardness. An ore of manganese, occurring usually with pyrolusite, and having similar origin and associations as that mineral.

Carbonates

The carbonates are grouped into two divisions: (1) Anhydrous Carbonates; (2) Acid, Basic and Hydrous Carbonates.

1. Anhydrous Carbonates

Calcite Group

The Calcite Group consists of a series of carbonates of the bivalent metals, calcium, magnesium, ferrous iron, manganese and zinc. They all crystallize in the rhombohedral class of the Hexagonal System with closely agreeing crystal constants. They all show a perfect rhombohedral cleavage, with the angle between the cleav age faces varying from 105° to 108°. The Calcite Group forms one of the most marked and important groups of isomorphous minerals, its chief members being as follows:

Calcite, CaC03. Dolomite, Magnesite, MgC03. Siderite, FeC03. Rhodochrosite, MnC03. Smithsonite, ZnC03.

J Calcite

Composition. Calcium carbonate, CaC03 Carbon dioxide 44.0, lime 56.0. Small amounts of magnesium, ferrous iron, manganese and zinc may replace the calcium.

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Crystallization. Hexagonal-rhombohedra,! . Crystals are veryvaried in habit, oftenlngTily corhpTex.TJver 300 different forms have been described. Three important habits: (1) Prismatic, in which the prism faces are prominent, in long or short prisms with basal plane or rhombohedral terminations (Figs. 276 and 277) ; (2) Rhombohedral, in which rhombohedral forms predominate, both low and steep rhombohedrons, the unit (cleavage) form is not common (Figs. 272, 273, 274 and 275) ; (3) Scalenohedral, in which the scalenohedrons predominate, often with prism faces and rhom bohedral truncations (Figs. 278, 279, 280, 281 and A, pi. VIII). All possible combinations and variations of these types. Twin ning according to several different laws frequent. Fig. 282 repre sents one type of twinning in which the basal plane is the twinning plane.

Structure. Crystallized or crystalline granular, coarse to fine. Also fine-grained to compact, earthy. In stalactitic forms, etc.

Physical Properties. Perfect cleavage parallel to unit rhombohedron (angle of rhombohedron 105° and 75°). H. 3. G. 2.72. Luster vitreous to earthy. Color usually white or colorless. May be variously tinted, gray, red, green, blue, yellow, etc. Also, when impure, brown to black. Usually transparent to translucent. Opaque when impure. Strong double refraction, hence the name doubly -ref rad ing spar.

Tests. Infusible. After intense ignition, residue gives alka line reaction to moistened test paper. Fragment moistened with hydrochloric acid and heated gives orange-red flame. Fragments effervesce freely in cold dilute hydrochloric acid. Concentrated solution gives precipitate of calcium sulphate when a few drops of sulphuric acid are added; no precipitate will form if solution is dilute. Distinguished by its softness (3), its perfect cleavage, light color, vitreous luster, etc. Distinguished from dolomite by the fact that fragments of calcite effervesce freely in cold hydro chloric acid, while those of dolomite do not.

Varieties. 1. Ordinary. Calcite in cleavable or crystalline masses. When transparent and colorless known as Iceland spar, because of its occurrence in quantity in Iceland.

2. Limestone, Marble, Chalk. Calcite exists in enormous quan-

Plate Viii.

A. Calcite, Joplin, Missouri.

B. Aragonite, Cleator Moor, England.

Calcite

Fig. 272.

Fig. 276.

Fig. 282.

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titles in the form of limestone rocks, which form a large part of the sedimentary strata of the earth. When these rock masses have been subjected to great heat and pressure they develop a crystalline structure, usually showing cleavage faces of greater or less size. Crystalline limestones are known as marble. On account of various impurities and through the presence in them of other minerals, they assume a wide range of colors, and form a long series of orna mental stones to which various names are given. Chalk is a very fine-grained, pulverulent deposit of calcium carbonate, occurring at times in large beds. It has been formed through the slow ac cumulation on the sea bottom of fragments of shells and of the skeletons of minute sea animals.

3. Cave Deposits, etc. Calcareous waters often deposit calcite in the form of stalactites, concretions, incrustations, etc. It is usually semitranslucent, of light-yellow colors. Many caves in limestone regions are lined with such deposits. Hot calcareous spring waters may form a deposit of calcite, known as travertine, around their mouths. Such a deposit is being formed at the Mammoth Hot Springs, Yellowstone Park.

4. Siliceous Calcites. Calcite crystals may inclose considerable amounts of quartz sand (up to 60 per cent) and form what are known as sandstone crystals. Such occurrences are— found at Fontainebleau, France (Fontainebleau limestone), and in the Bad Lands, South Dakota.

Occurrence. Calcite is one of the most common and widely diffused of minerals. It occurs as enormous and widespread sedi mentary rock masses, in which it is the predominant, at times prac tically the only mineral present. Such rocks are the limestones, marbles (metamorphosed limestones), chalks, calcareous marls, cal careous sandstones, etc. The limestone rocks have, in great part, been formed by the deposition on a sea bottom of great thicknesses of calcareous material in the form of shells, skeletons of sea ani mals, etc. A smaller proportion of these rocks have been formed directly by precipitation of calcium carbonate. It occurs as a secondary mineral in igneous rocks as a product of decomposition of lime silicates. It is found lining the amygdaloidal cavities in lavas. It occurs in many sedimentary and metamorphic rocks in greater or less proportion. It is the cementing material in the lightcolored sandstones. Calcite is also one of the most common of

Calcite

vein minerals, occurring as a gangue material, with all sorts of metallic ores.

It would be quite impossible to specify all of the important dis tricts for the occurrence of calcite in its various forms. Some of the more notable localities in which finely crystallized calcite is found are as follows: Andreasberg in the Harz Mountains; various places in Saxony; in Cumberland, Derbyshire, Durham, Cornwall, Lan cashire, England; Iceland; Guanajuato, Mexico; Joplin, Missouri; Lake Superior copper district; Rossie, New York, etc.

Use. The most important use for calcite is for the manufacture of lime for mortars and cements. Limestone when heated to about 1000° F. loses its carbonic acid, and is converted into quick lime, CaO. This, when mixed with water (slaked lime), swells, gives off much heat, and finally by absorption of carbon dioxide from the air hardens, or, as commonly termed, "sets." Quicklime when mixed with sand forms the common mortar used in building. Certain limestones contain various clayey materials as impurities. Cements made from these limestones have the valuable property of hardening under water, and are known as hydraulic cements. Many hydraulic cements are made up artificially by combining their ingredients in experimentally determined proportions. The chemistry of the process of their hardening is not fully under stood, but various silicates of calcium and aluminum are probably formed. Portland cement, used so largely in concrete construc tion, is a mixture of about 6 parts of lime, 2 parts of silica, and 1 part of alumina.

Chalk is used as a fertilizer, for whiting and whitewash, for crayons, etc. It is found in many places in Europe, the chalk cliffs of Dover being famous.

Limestone is largely used as a building material, and is obtained in the United States chiefly from Pennsylvania, Indiana, Ohio, Illinois, New York, Missouri, Wisconsin. Limestone is largely used as a flux for smelting various metallic ores. A fine-grained limestone is used in lithographing.

Marbles are used very extensively as ornamental and building material. The most important marble quarries in the United States are found in Vermont, New York, Georgia, Tennessee, etc.

Iceland spar is valuable for optical instruments, being used in

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the form of the Nicol prism to produce polarized light. Obtained at present only from Iceland.

Dolomite

Composition. Carbonate of calcium and magnesium, CaMg- Carbon dioxide 47.8, lime 30.4, magnesia 21.7. Varie ties occur in which the proportion of CaC03 to MgC03 is not as 1:1. Small amounts of ferrous carbonate frequently replace some of the magnesium carbonate. Manganese is also present at times.

Fig. 283. Fig. 284.

Crystallization. Hexagonal-rhombohedral. Crystals are usually the unit rhombohedron (cleavage rhombohedron) (Fig. 283). Faces often curved, and sometimes so acutely as to form "saddle-shaped" crystals (Fig. 284). Other forms rare.

Structure. In coarse, granular, cleavable masses to fine grained and compact and in crystals.

Physical Properties. Perfect rhombohedral cleavage (cleav age angle 106° 15'). H. 3.5-4. G. 2.85. Vitreous lus ter; pearly in some varieties (pearl spar). Color usually some shade of pink, flesh color; may be colorless, white, gray, green, brown and black. Transparent to translucent.

Tests. Infusible. After intense ignition a fragment will give an alkaline reaction to moistened test paper. Readily soluble, with effervescence in hot hydrochloric acid; fragment only slowly attacked by cold dilute acid (difference from calcite). Solution oxidized by nitric acid arid then made ammoniacal (may pre cipitate ferric hydroxide) will with ammonium oxalate give a write precipitate of calcium oxalate; filtrate with sodium phos-

Magnesite

phate gives granular white precipitate of ammonium magnesium phosphate. Crystallized variety told by its curved rhombohedral crystals and usually by its flesh-pink color.

Occurrence. Dolomite occurs chiefly in widely extended rock masses as dolomite limestone and marble. Occurrence same as for calcite rocks. The two varieties can only be told apart by tests, the simplest being to see if a drop of cold hydrochloric acid placed on the rock will produce effervescence (if so, rock is calcite; if not, dolomite). Often intimately mixed with calcite. Dolomite as a rock mass is thought to be secondary in origin, having been formed from ordinary limestone by the action of solutions containing mag nesium. Occurs also as a vein mineral, chiefly in the lead and zinc veins that traverse limestone. Found in large rock strata in the dolomite region of southern Tyrol; in crystals from the Binnenthal, Switzerland; Traversella in Piedmont; northern England; Guana juato, Mexico; Joplin, Missouri, etc.

Use. As a building and ornamental stone. For the manufac ture of certain cements. For the, manufacture of magnesia, used in the preparation of refractory linings of the converters in the basic steel process.

Atikerite, is a subspecies intermediate between calite, dolomite and siderite.

Magnesite

Composition. Magnesium carbonate, MgC03 Carbon di oxide 52.4, magnesia 47.6. Iron carbonate also often present.

Crystallization. Ijexagonal-rhombohedral . In rhombohedral crystals.

Structure. Compact earthy forms common, also less fre quently in cleavable granular masses, coarse to fine. Crystals rare.

Physical Properties. Perfect rhombohedral cleavage, some times distinct. H. 3.5-4.5. G. 3-3.1. Vitreous luster. Color white, gray, yellow, brown. Transparent to opaque.

Tests. Infusible. After intense ignition gives a faint alkaline reaction on moistened test paper. Scarcely acted upon by cold but dissolves with effervescence in hot hydrochloric acid. Solu tion, after the precipitation of any iron and calcium, gives in the

Manual Of Mineralogy

presence of an excess of ammonia, with sodium phosphate, a white granular precipitate of ammonium magnesium phosphate.

Occurrence. Commonly derived from the alteration of rocks rich in magnesium, through the action of waters containing carbonic acid. Such magnesites are commonly colloidal in character and often con tain opal silica. Crystallized magnesite is formed in various ways. Large bodies of what is considered to be sedimentary magnesite have been found in western United States. Associated with serpentine, dolomite, brucite, etc. Magnesite occurs in the Coast Range of California, and in sedimentary beds in Clark Co., Nevada and in the Mohave Desert, California. Most of the magnesite used in the United States is imported, coming chiefly from Strvia in Austria and from Greece. —

Use. Magnesite is chiefly used in the preparation of magnesite bricks for refractory linings in metallurgical furnaces. Also used in the preparation of magnesium salts (Epsom salts, magnesia, etc.).

Siderite. Spathic Iron. Chalybite

Composition. Ferrous carbonate, FeC03 Carbon dioxide 37.9, iron protoxide 62.1, non 48.2. Manganese, magnesium and calcium may be present in small amounts.

Crystallization. Hexagonal-rhombohedral. Ciystals usually unit rhombohedrons (same as cleavage form), frequently with curved faces.

Structure. Usually cleavable granular. At times botryoidal, compact and earthy. More rarely in crystals.

Physical Properties. Perfect rhombohedral cleavage (cleav age angle 107°). H. 3.5-4. G. 4.5-5. Vitreous luster. Color usually light to dark brown. Transparent to opaque.

Tests. Difficultly fusible (4.5-5). Becomes strongly mag netic on heating. Heated in C. T. decomposes and gives a black magnetic residue. Soluble in hydrochloric acid with effervescence; solution gives with potassium ferricyanide a dark blue precipitate (test for ferrous iron). Recognized usually by its color and cleavage.

Varieties. 1. Crystallized. In crystals or granular cleavable masses.

Rhodochrosite

2. Concretionary. In globular concretions.

3. Clay Ironstone. Impure by admixture with clay materials. Sometimes in concentric layers. Forms stratified bodies with coal formations, etc.

4. Black-band Ore. An impure stratified deposit of siderite, containing considerable carbonaceous matter. Associated with coal beds.

Occurrence. Found in the form of clay ironstone and black-band ore in extensive stratified formations lying in clay or slate rocks and commonly associated with coal measures. These ores are the chief source of iron in Great Britain and are found in Staffordshire, York shire and Wales. Clay ironstone is also abundant in the coal measures of western Pennsylvania and eastern Ohio, but it is not used to any great extent as an ore. Siderite is also formed by the replace ment action of ferrous solutions upon limestones. Siderite, in its crystallized form, is a common vein mineral associated with various) metallic ores, as silver minerals, pyrite, chalcopyrite, tetrahedrite, galena, etc.

Name. The original name for the mineral was spherosiderite, given to the concretionary variety and subsequently shortened to siderite to apply to the entire species. Spathic ore is a common name. Chalybite, used by some mineralogists, was derived from the Chalybes, who lived on the Black Sea, and were in ancient times workers in iron.

Use. An ore of iron. Important in Great Britain, but of very subordinate value in the United States.

Rhodochrosite

Composition. Manganese protocarbonate, AInC03 Carbon dioxide 38.3, manganese protoxide 61.7. Iron is usually present, replacing a part of the manganese and sometimes calcium, mag nesium, zinc, etc.

Crystallization. Hexagonal-rhombohedral. Crystals unit rhombohedrons (same as cleavage rhombohedron), frequently with curved faces.

Structure. Usually cleavable massive; granular to compact. Rarely in crystals.

Manual Of Mineralogy

Physical Properties. Perfect rhombohedral cleavage (cleav age angle 107°). H. 3. 5-4. 5. G. 3.45-3.6. Vitreous luster. Color usually some shade of rose-red; may be light pink to dark brown. Transparent to translucent.

Tests. Infusible. Soluble in hot hydrochloric acid with effervescence. Gives reddish violet color to borax bead when heated in 0. F. Told usually by its pink color, rhombohedral cleavage and hardness (4). Distinguished by its hardness from rhodonite (MnSi03) (H. 5.5-6.5).

Occurrence. A comparatively rare mineral, occurring in veins with ores of silver, lead and copper, and with other manganese minerals. Found in the silver mines of Rumania and Saxony. In the United States at Branchville, Connecticut; Franklin, New Jer sey; in good crystals at Alicante, Lake Co., at Alma, Park Co., and elsewhere in Colorado.

Name. Derived from two Greek words meaning rose and color, in allusion to its rose-pink color.

Use. A minor ore of manganese.

Smithsonite

Composition. Zinc carbonate, ZnC03 Carbon dioxide 35.2, zinc protoxide 64.8. Iron and manganese often replace a part of the zinc; also at times calcium and magnesium.

Crystallization. Hexagonal-rhombohedral. Rarely in small rhombohedral or scalenohedral crystals.

Structure. Usually reniform, botryoidal or stalactitic and in crystalline incrustations or in honeycombed masses known as dry-bone ore. Also granular to earthy. Distinct crystals rare.

Physical Properties. Perfect rhombohedral cleavage, which, on account of the usual structure, is seldom observed. H. 5 (unusually high for a carbonate). G. 4.30-4.35. Vitreous luster. Color usually dirty brown. May be white, green, blue, pink, etc. Translucent to opaque.

Tests. Infusible. Soluble in hydrochloric acid with effer vescence. A fragment heated B. B. in R. F. gives bluish green streaks in the flame, due to the burning of the volatilized zinc.

Aragonite Group

Heated in R. F. on charcoal gives a nonvolatile coating of zinc oxide, yellow when hot, white when cold; if coating is moistened with cobalt nitrate and again heated it turns green. Distin guished by its effervescence in acids, its tests for zinc, its hardness (5) and its high specific gravity.

Occurrence. It is a zinc ore of secondary origin. Found in con nection with zinc deposits near the surface, and where the oxidized ores have been acted upon by carbonated waters. Common in connection with zinc deposits lying in limestone rocks. Associated with sphalerite, galena, calamine, cerussite, calcite, limonite, etc. Often found in pseudomorphs after calcite. " Dry-bone ore" is a honeycombed mass, with the appearance of dried bone, whose structure has resulted from the manner of deposition of the mineral. Some calamine, the silicate of zinc, is included under the term. Occurs, as an ore, in the zinc deposits of Missouri, Arkansas, Wis consin, Virginia, etc. Found at times in translucent green or greenish blue material which is available for ornamental uses. Such smithsonite is found at Laurium, Greece, and at, Kelly, Naw Mexico. In yellow stalactites with banded structure from Sardinia.

Name. Named in honor of James Smithson (1754-1829), who founded the Smithsonian Institution at Washington. Eng lish mineralogists call the mineral calamine, using either electric calamine or hemimorphite as the name for the silicate.

Use. An ore of zinc.

Aragonite Group

The Aragonite Group consists of a series of carbonates of the bivalent metals, calcium, strontium, barium and lead, which crystallize in the Orthorhombic System with closely related crys tal constants and similar habits of crystallization. All of them appear at times in twin crystals which are pseudohexagonal in character. The members of the group are:

Aragonite, CaC03.

Strontianite, SrC03.

Witherite, BaC03.

Cerussite, PbC03.

Manual Of Mineralogy

Aragonite

Composition. Calcium carbonate, like calcite, CaCOs Car bon dioxide 44, lime 56. May contain a little strontium or lead, rarely zinc.

Crystallization. Orthorhombic. Three prominent habits of crystallization: (1) Acicular pyramidal; consisting of a prism terminated by a combination of a very steep pyramid and brachydome (see Fig. 285; and B, pi. VIII). Usually in radiating groups of large to very small crystals. (2) Tabular; consisting of promi nent brachypinacoid faces modified by a prism and a low brachydome (Fig. 286). Often twinned with a prism face as a twinning

plane (Fig. 287). (3) In pseudohexagonal twins (Fig. 288).

This type shows a hexagonal-like prism terminated by a basal plane, and is formed by an intergrowth of three individuals with basal planes in common and their prism faces falling partly in the same plane, and partly with only slightly different positions. The crystals are distinguished from true hexagonal forms by noting that the basal plane is striated in three different directions, and also by the fact that, because the prism angle of the simple crystals is not exactly 60°, the composite prism faces for the twin w'ill often show slight reentrant angles.

Structure. In crystals. Also reniform, columnar, stalactitic, etc.

Wither! Te

Physical Properties. Vitreous luster. Colorless, white, pale yellow and variously tinted. Transparent to translucent. H. 3.5-4. G. 2.95 (harder and heavier than calcite).

Tests. Infusible. Decrepitates. After intense ignition the powder gives an alkaline reaction on moistened test paper. Frag ments fall to powder (change to calcite) when heated at low redness in C. T. Chemical tests same as for calcite (page 218). Dis tinguished from calcite by its lack of cleavage, and the fact that fragments fall to powder when heated in C. T.

Occurrence. Less stable than calcite and much less common in its occurrence. Usually found as a vein mineral. Experiments have shown that carbonated waters containing calcium more often deposit aragonite when they are hot and calcite when they are cold. Some sea shells are composed entirely or in part of aragonite. The pearly layer of many shells is aragonite. It has been noted that the aragon ite shells are not readily preserved as fossils, being easily dissolved or disintegrated, or at times apparently slowly changing to calcite. Aragonite is most commonly found associated with beds of gypsum and deposits of iron ore (where it sometimes occurs in forms resem bling coral, and is called flos Jerri, flower of iron). At times found lin ing amygdaloidal cavities in basalt. Found frequently with pyrite, chalcopyrite, galena, malachite, etc. Notable localities for the various crystalline types are as follows: Pseudohexagonal twin crystals are found in Aragon, Spain; Bastennes, in the south of France; and at Girgentt, JhcnyT 'i'he tabular type of crystals is found near Bilin, Bohemia. The acicular type is found at Alston Moor and Cleator Moor, Cumberland, England. Flos ferri is found in the Stryian iron mines. The flos-ferri variety occurs in the Organ Mts., New Mexico and in Bisbee, Arizona.

Witherite

Composition. Barium carbonate, BaCCb Carbon dioxide 22.3, barium oxide 77.7.

Crystallization. Orthorhombic. Crystals always twinned, forming pseudohexagonal pyramids by the intergrowth of three individuals terminated by brachydomes (Fig. 289). Crystals sometimes doubly terminated; often deeply striated horizontally and by a series of reentrant angles have the appearance of one pyramid capping another.

Manual Of Mineralogy

Structure. In twin crystals, also botryoidal to globular; columnar or granular.

Physical Properties. H. 3.5. G. 4.3. Vitreous luster. Colorless, white, gray. Translucent.

Tests. Easily fusible at 2.5-3, giving a yellowish green flame (barium). After intense ignition gives an alkaline reaction on moistened test paper. Soluble in hydrochloric acid W'ith effer vescence. All solutions, even the very dilute, give precipitate of barium sulphate with sulphuric acid (difference from calcium and strontium). Heavy.

Occurrence. A comparatively rare mineral, most frequently found in veins associated with galena. Found in fine crystals near Hexham in Northumberland and Alston Moor in Cumberland. Occurs at Leogang in Salzburg; near Lexington, Kentucky; Thunder Bay, Lake Superior, Ontario.

Use. A minor source of barium compounds.

Strontianite

Composition. Strontium carbonate, SrC03 Carbon dioxide 29.9, strontia 70.1. A little calcium sometimes present.

Crystallization. Orthorhombic. Crystals usually acicular, like type (1) under aragonite. Twinning also frequent, giving at times pseudohexagonal forms.

Structure. Radiating crystallized, also columnar; fibrous and granular.

Physical Properties. H. 3.5-4. G. 3.7. Vitreous lus ter. White, gray, yellow, green. Transparent to translucent.

Tests. Infusible. On intense ignition throws out fine branches and gives a crimson flame (strontium) and residue gives alkaline reaction on moistened test paper. Effervescence in hydrochloric acid, and the mediumly dilute solution will give precipitate of strontium sulphate on addition of a few drops of sulphuric acid; no precipitate will form in the very dilute solution (difference from

Cerussite

calcium and barium). Usually necessary to make the above tests to determine the mineral.

Occurrence. A comparatively rare mineral found in veins in limestones or marls, and less frequently in eruptive rocks. Some times in metallic veins. Originally found at Strontian in Argyllshire. In commercial deposits in Westphalia; at Schoharie, New York, etc.

Use. Has no great commercial use. A minor source of stron tium compounds, used in fireworks and in the separation of sugar from molasses.

Cerussite

Composition. Lead carbonate, PbC03 Carbon dioxide 16.5, lead oxide 83.5.

Crystallization. Habit varied and crystals show many forms. Crystals often tabular parallel to brachy-pinacoid (Fig. 290). Frequently twinned, forming lattice-like groups with the plates crossing each other at 60° angles (pi. IX).

Sometimes pyramidal in habit; also twinned in pseudohexagonal pyramids, frequently with deep reentrant angles in the prism zone.

Structure. In crystals or in granular crys talline aggregates; fibrous; granular massive; compact; earthy.

Physical Properties. H. 3-3.5. G. 6.55 (high for a mineral with nonmetallic luster).

Adamantine luster. Colorless, white or gray.

Transparent to almost opaque.

Tests. Easily fusible (1.5). With sodium carbonate B. B. on charcoal gives globule of lead and yellow to white coating of lead oxide. Soluble in warm dilute nitric acid with effervescence. In C. T. usually decrepitates and is changed to lead oxide, which is dark yellow when hot. Recognized by its high specific gravity, white color and adamantine luster.

Occurrence. An important and widely distributed lead ore of secondary origin, formed by the oxidation of galena in the presence of carbonated waters. Found in the upper and oxidized zone of lead veins, associated with galena, anglesite, sphalerite, smithsonite,

Manual Of Mineralogy

silver ores, etc. Notable localities for its occurrence are Ems in Nassau; Mies, Bohemia; Nerchinsk, Siberia; on the island of Sar dinia; in Tunis; at Otavi, South West Africa; Broken Hill, New South Wales; Phcenixville, Pennsylvania; Leadville, Colorado, various districts in Arizona; from the Organ Mts., New Mexico; in the Coeur d'Alene district in Idaho, etc.

Use. An important ore of lead.

Phosgenite, a chlorocarbonate of lead tetragonal in crystallization, is a rare member of the Anhydrous Carbonate Division.

2. Acid, Basic And Hydrous Carbonates

Malachite. Green Copper Carbonate

Composition. Basic carbonate of copper, fCp OHkCQ — or Carbon dioxide 19.9, cupric oxide 71.9, water 8.2. Copper 57.4.

Crystallization. Monoclinic. Crystals usually slender pris matic but seldom distinct.

Structure. Usually radiating fibrous with botryoidal or stalactitic structure (see Fig. C, pi. III). Often granular or earthy.

Physical Properties. Perfect basal cleavage. H. 3.5-4. G. 3.9-4.03. Adamantine to vitreous luster in crystals; often silky in fibrous varieties; dull in earthy type. Color bright green. Translucent to opaque.

Tests. Fusible (3), giving a green flame. With fluxes in R. F. on charcoal gives copper globule. Soluble in hydrochloric acid with effervescence. Solution turns deep blue with excess of am monia. Much water in C. T. Recognized by its bright green color and radiating fibrous structure.

Occurrence. An important and widely distributed copper ore of secondary origin. Found in the oxidized portions of copper veins associated with azurite, cuprite, native copper, iron oxides and the various sulphides of copper and iron. Usually occurs in copper veins that lie in limestones, Notable localities for its occurrence

Plate Ix.

Cerussite, Broken Hill, New South Wales.

Aurichalcite

are at Nizhne Tagilsk in the Ural Mountains; at Chessy, near Lyons, France, associated with azurite; from near Otavi, South West Africa; from Rhodesia; South Australia; etc. In the United States, an im portant copper ore in the southwestern copper districts; at Bishee, Morenci. and other localities in Arizona: in New Mexico.

Name. Derived from the Greek word for mallows, in allusion to its green color.

Use. An important ore of copper. Has been used to some extent as an ornamental material for vases, veneer for table tops, etc.

Azurite. Chessylite. Blue Copper Carbonate

Composition. A basic carbonate of copper, or Carbon dioxide 25.6, cupric oxide 69.2, water 5.2. Copper 55.3.

Crystallization. Monnclinic. Habit varied. Crystals fre quently complex and distorted in development, sometimes in radiating spherical groups.

Structure. Crystallized. In radiating botryoidal structure. Earthy.

Physical Properties. H. 3.5-4. C. 3.77. Vitreous lus ter. Intense azure-blue color. Transparent to opaque.

Tests. Same as for malachite (which see). Characterized chiefly by its azure-blue color.

Occurrence. Origin and associations same as for malachite. Found in fine crystals at Chessy, near Lyons, France; in Rumania; at Laurium, Greece; in Siberia; at Broken Hill, New South Wales; in Arizona at Copper Queen Mine, Bisbee; at Morenci, etc. Widely distributed with copper ores. Not so common as malachite.

Name. Named in allusion to its color.

Use. An important ore of copper.

Aurichalcite

A basic carbonate of zinc and copper, In acicular crystals, forming drusy incrustations. H. 2. G. 3.6. Pearly luster. Color pale green to blue. Infusible. Soluble in hydrochloric acid with effervescence. Solution turns blue

Manual Of Mineralogy

with ammonia in excess. Fused in R. F. on charcoal with sodium carbonate gives a nonvolatile coating of zinc oxide (yellow when hot, white when cold). Water in C. T. A rare mineral, found in the oxidized zones of copper veins.

Gay-Lussite

A hydrous carbonate of calcium and sodium, CaCO3.Na2CO3.5H2O. Monoclinic. In rude crystals with uneven surfaces. Often wedgeshaped. Prismatic cleavage. H. 2-3. G. 1.99. Vitreous luster. Colorless, white, gray. Fusible at 1.5, giving yellow flame of sodium. Gives alkaline reaction after ignition. Effervesces in acids. Concentrated hydrochloric acid solution gives precipitate of calcium sulphate with sulphuric acid. A rare species, found in saltlake deposits at Lagunillas, Venezuela, and near Ragtown, Nevada.

Other rarer species in this division include hydrozincite, ZnC03.- trona , Na> C 0 3 . II NaC 0 3 . 2 1 1 2 0; hydromagnesite, 3MgC03.-

Silicates

The silicates form the largest single section of the Chemical Classification of Minerals. They may be divided into (1) An hydrous Silicates, (2) Hydrous Silicates.

Anhydrous Silicates

This section may be subdivided into (1) Disilicates, Poly sili cates, being salts of disilicic acid, H2Si205, or polysilicic acid, ILShOgj (2) Metasilicates, being salts of metasilicic acid, H2Si03; (3) Orthosilicates, being salts of orthosilicic acid, II,Si04; (4) Subsilicates, including various basic species.

1. Disilicates, Polysilicates

The only representative of the disilicates of sufficient impor tance to warrant mention here is the rare lithium mineral, petalite,

Orthoclase

The Feldspar Group

The feldspars form one of the most important of mineral groups. They are polysilicates of aluminum with either potassium, sodium and calcium and rarely barium. They may belong to either the monoelinic or the triclinic systems but with the crystals of the different species resembling each other closely in angles, habits of crystallization, and methods of twinning. They all show cleavages in two directions which make an angle of 90°, or closely 90°, with each other. Hardness is about 6 and specific gravity 2.6.

Monoclinic Section

Orthoclase. Potash Feldspar

Composition. Potassium-aluminum silicate, KAlSi3Os Silica 64.7, alumina 18.4, potash 16.9. Soda sometimes replaces a por tion of the potash.

Crystallization. Monoclinic. Crystals are usually prismatic in habit and have as prominent forms, clinopinacoid, base, prism, with often smaller orthodomes (Figs. 291, 292 and 293). Fre-

Fig. 291.

Fig. 292.

Fig. 293.

quently twinned; Carlsbad with clinopinacoid as twinning plane (Fig. 294); Baveno with clinodome as twinning plane (Fig. 295); Manebach with base as twinning plane (Fig. 296).

Structure. Usually crystallized or coarsely cleavable to granu lar; more rarely fine-grained, massive and cryptocrystalline.

Physical Properties. Two prominent cleavages (one parallel to base, perfect: the other parallel to clinopinacoid, good), mak-

Manual Of Mineralogy

ing an angle of 90° with each other. H. 6-6.5. G. 2.5-2.6. Luster vitreous. Colorless, white, gray, flesh-red, more rarely green. Streak white.

Fig. 294. Fig. 295. Fig. 296.

Carlsbad Twin. Baveno Twin. Manebach Twin.

Varieties. Common feldspar is the usual opaque variety. Adularia is white or colorless and translucent to transparent. Some adularia shows an opalescent play of colors, and is called moonstone. Most of the moonstones, however, belong to the members of the plagioclase feldspar series. Sanidine, or glassy feldspar, is a variety occurring in glassy, often transparent, phenocrysts in eruptive rocks.

Tests. Difficultly fusible (5). Insoluble in acids. When mixed with powdered gypsum and heated on platinum wire gives the violet flame of potassium. Usually to be recognized by its color, hardness and cleavage. Distinguished from the other feldspars by its right-angle cleavage and the lack of striations on the best cleavage surface.

Alteration. When acted upon by waters carrying carbon dioxide in solution, orthoclase alters, forming a soluble carbonate of potassium and leaving as a residue either a mixture of kaolin (HiAhShOsi) and quartz (Si02), or of muscovite and quartz. Kaolin forms the chief constituent of clays and has been derived in this manner.

Microcline

Occurrence. One of the most common of minerals. It is formed during the crystallization of igneous rocks; by pneumatolytic and hydrothermal agencies in pegmatite veins and in druses in the rocks. More rarely by crystallization from aqueous solutions at low tem peratures in veins. W idely distributed as a prominent rock constit uent, occurring in all types of rocks; igneous, in granites, syenites, porphyries, etc.; sedimentary, in certain sandstones and conglomer ates; metamorphic, in gneisses. Also in large crystals and cleavable masses in pegmatite veins, associated chiefly with quartz, muscovite and albite. These veins are to be found where granite rocks abound. Large veins of this character from which feldspar is quarried in con siderable amounts occur in the New England and Middle Atlantic states, chiefly in Maine, Connecticut, New York, Pennsylvania and Maryland.

Name. The name orthoclase refers to the right-angle cleavage possessed by the mineral. Feldspar is derived from the German word / eld, field.

Use. Orthoclase is chiefly used in the manufacture of porce lain. It is ground very fine and mixed with kaolin, or clay, and quartz. When heated to high temperature the feldspar fuses and acts as a cement to bind the material together. Fused feldspar also furnishes the major part of the glaze on porcelain ware.

A rare barium feldspar, hyalophane belongs here.

Triclinic Section

Microcline

Composition. Like orthoclase, KAlSi308 Silica 64.7, alu mina 18.4, potash 16.9.

Crystallization. Triclimc. Axial lengths and angles only slightly different from those of orthoclase. Ordinarily the crys tals of the two species cannot be told apart except by very accu rate measurements or a microscopical examination. Microcline crystals are usually twinned according to the same laws as ortho clase. Also microscopically twinned according to the albite and pericline laws, characteristic of the triclinic feldspars. A thin section of microcline under the microscope in polarized light usu ally shows a characteristic grating structure, caused by the crossing

Manual Of Mineralogy

at nearly right angles of the twin lamellae formed according to these triclinic twinning laws. Orthoclase, being monoclinic, could not show such twinning.

Structure. In cleavable masses or in crystals.

Physical Properties. Cleavage parallel to base and brachypinacoid, with angle of 89° 30' (orthoclase would have 90°). H. 6-6.5. G. 2.54-2.57. Vitreous luster. Color white to pale yellow. Also sometimes green (Amazon stone ) or red. Trans parent to translucent.

Tests. Same as for orthoclase. The two species only to be distinguished from each other by careful examination (see above).

Occurrence. Same as for orthoclase. Much that passes as ortho clase in reality is microcline. Occurs with a green color in the Ural Mts. and at Pike's Peak, Colorado, and is known as Amazon stone.

Name. Microcline is derived from two Greek words meaning little and inclined, referring to the slight variation of the cleavage angle from 90°.

Use. Same as for orthoclase. Amazon stone is at times pol ished and used as an ornamental material.

The Plagioclase Feldspars. Albite-Anorthite

Series

The triclinic soda-lime feldspars embrace a series of isomorphous minerals varying in composition from albite, NaAlSi308, to anorthite, CaAl2Si208. These two molecules can replace each other in any proportion, and as a consequence a practically com plete series may be found from the pure soda feldspar, and then with gradually increasing amounts of the anorthite molecule, to the pure lime feldspar. Definite names have been given to various mixtures of these two molecules, the more important being listed below:

Albite, NaAlShOs.

Oligoclase, 3NaAlSi308.lCaAl2Si208.

Andesine, lNaAlSi308.lCaAl2Si208.

Labradorite, lNaAlSi308.3CaAl2Si208.

Anorthite, CaAI2Si208.

The Plagioclase Feldspars

These triclinic feldspars crystallize in forms closely resembling those of the monoclinic orthoclase, and the axial lengths and in clinations are also closely the same. This similarity in the crys tal structure between the monoclinic and triclinic feldspars is best shown by a comparison of the cleavage angles of the different species, that of orthoclase being 90°, of albite 86° 24', and of anorthite 85° 50'. The triclinic feldspars are often known as the plagioclase feldspars, because of their oblique cleavage.

The crystals of the plagioclase feldspars are frequently twinned according to the various laws governing the twins of orthoclase, i.e., the Carlsbad, Baveno and Manebach laws. They are also practically always twinned according to one or both of two laws, known as the albite and pericline laws. The twinning plane in the albite law is the brachypinacoid which corresponds-ta the djqnpinamid in orthoclase. The angle between the basal plane and this twinning plane is not 90°, but about 86°; so that if one imagines a triclinic feldspar crystal cut in two along this plane and one-half revolved 180° from its original position upon an axis perpendicular to the plane, there would then be formed a shallow trough along the upper surface of the crystal, because the basal planes of the two adjacent halves would not lie in the same plane, but rather slope at a slight angle toward each other. This sort of twinning is commonly repeated many times in a single crystal, and gives rise to thin lamellae, each one in twin position in respect to those on either side (see Figs. 299 and 300). Consequently a basal plane or cleavage surface of such a twinned crystal will be crossed by a number of parallel groovings or striations (Fig. 301). Many times these striations are so fine as not to be visible to the unaided eye, but also at times they are coarse and easily seen. The presence of these striation lines upon the better cleavage sur face of a feldspar is one of the best proofs that it belongs to the plagioclase series. In the pericline law the twinning axis is the b crystallographic axis, and when this results in polysynthetic twins the consequent striations are to be seen on the brachypinacoid.

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Albite. Soda-feldspar

Composition. Sodium-aluminum silicate, NaAlSi308 Silica 68.7, alumina 19.5, soda 11.8. Calcium is usually present in small amount in the form of the anorthite molecule, CaAl2Si208.

Crystallization. Triclinic. Usually in tabular crystals paral lel to brachypinacoid (Fig. 297). Sometimes elongated parallel

Fig. 297.

Fig. 298. Fig. 299. Albite Twin.

Fig. 300. Fig. 301. Albite Twinning.

to b crystal axis (Fig. 298). Twinning very common, according to the albite law (see above) and evidenced by fine striation lines on the better cleavage surface (Figs. 300 and 301). Twinning according to the other laws frequent.

Structure. Commonly massive, either lamellar with lamellae often curved or in cleavable masses. Distinct crystals rare.

Oligoclase

Physical Properties. Perfect cleavage parallel to base; good cleavage parallel to brachypinacoid. Cleavage angle 86° 24'. H. =6. G. 2.62. Vitreous luster; sometimes pearly on cleav age surface. Colorless, white, gray. Transparent to opaque.

Tests. Fusible at 4-4.5, giving yellow flame (sodium). In soluble in acids. Characterized by its hardness, white color, cleavage, frequently curved lamellar structure, striations on better cleavage surface, etc.

Occurrence. Like orthoclase, a widely distributed and important rock-making mineral. It occurs in all classes of rocks, but particu larly in those of igneous origin, such as granites, syenites, porphy ries and felsite lavas. Found commonly, also, in pegmatite veins. Frequently occurs in gneiss, less often in the crystalline schists. May occur in veins. At times in disseminated crystals in granular limestone and marble. Notable localities for crystallized albite are to be found in Switzerland and the Tyrol; in the United States at Paris, etc., Maine; Chesterfield, Massachusetts; Haddam and Branchville, Connecticut; Amelia Court House, Virginia, etc.

Name. From the Latin albus, white, in allusion to its color.

Use. Has the same uses as orthoclase, but not so commonly employed. Some varieties, when polished, show an opalescent play of colors and are known as moonstones. Other members of the plagioclase series and orthoclase show at times this same effect. The stones are usually cut in round or oval shapes. The finest moonstones come from Ceylon, but they are chiefly ortho clase.

Oligoclase

Composition. Intermediate between albite and anorthite, chiefly near SNaAlSbOa-lCaAbSLOs.

Crystallization. Triclinic. Like albite.

Structure. Usually massive, cleavable to compact. Crystals

rare.

Physical Properties. Cleavage in two directions at 86° 32'. One cleavage (parallel to base) is better than the other, and on this parallel striation lines due to twinning are commonly to be seen. H. =6. G. 2.66. Vitreous to pearly luster. Color

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usually whitish with faint tinge of grayish green, also reddish white, etc. Translucent to opaque.

Tests. Fusible at 4-4.5. Insoluble in hydrochloric acid. To be told from albite only by a test for calcium. Briefly, the test is made as follows: Fuse powdered mineral with sodium carbonate; dissolve fusion in hydrochloric acid and evaporate to dryness, moisten residue with water and a little nitric acid, boil and then filter off insoluble silica; to filtrate add ammonium hydroxide in excess, filter off precipitate of aluminum hydroxide; in filtrate get precipitate of calcium oxalate upon addition of ammonium oxalate. To be positively distinguished from andesine and labradorite only by a chemical analysis or an optical examination.

Occurrence. Like albite, but not so common. Especially char acteristic of the more acid igneous rocks. Found in various localities in Norway, notably at Tvedestrand, where it contains inclusions of hematite, which give the mineral a golden shimmer and sparkle. Such feldspar is called aventurine oligoclase, or sunstone. Occurs in the United States at Fine, St. Lawrence County, New York; Danbury, Connecticut; Bakersville, North Carolina, etc.

Name. Derived from two Greek words meaning little and fracture.

Use. Occasionally used as an ornamental material, in the varieties sunstone and moonstone.

Andesine

Composition. Intermediate between albite and anorthite, corresponding chiefly to lNaAlSisOs.lCaALSLOs.

Crystallization. Triclinic. Like albite.

Structure. In cleavable masses. Crystals rare.

Physical Properties. Cleavage in two directions at 86° 14'. One cleavage (parallel to base) better than the other, and on this parallel striation lines due to twinning are commonly to be seen. H. =6. G. 2.69. Vitreous to pearly luster. Color white, gray, greenish, yellowish, flesh-red. Often exhibits a beautiful play of colors, due partly to the intimate twinning and partly to inclusions.

An Orth I Te

Tests. Same as for oligoclase. To be positively distinguished from oligoclase and labradorite only by a chemical analysis or an optical examination.

Occurrence. Same as for albite, but less common. More fre quently found in somewhat more basic igneous rocks, i.e., those con taining less silica and more lime and magnesia.

Name. Occurs in a rock called andesite, found in the Andes Mountains.

Labradorite

Composition. Intermediate between albite and anorthite, corresponding chiefly to lNaAlSLOs-SCaAkSkOg.

Crystallization. Triclinic. Like albite.

Structure. In cleavable masses. Crystals rare.

Physical Properties. Cleavage in two directions at 86° 5'. One cleavage (parallel to base) better than the other, and on this parallel striation lines due to twinning are commonly shown. H. =6. G. 2.73. Vitreous luster. Usually gray, brown or greenish; sometimes colorless or white. Often shows a beautiful play of colors, due in part to the intimate twinning structure, in part to inclusions. Transparent to opaque.

Tests. Same as for oligoclase.

Occurrence. Like albite, but more commonly in the darker colored basic igneous rocks, and usually associated with pyroxene or amphibole. Thus, it occurs in diorite, gabbro, norite, andesite, basalt, etc. Found on the coast of Labrador in large amounts, as sociated with hypersthene and magnetite, and when polished showing a fine iridescent play of colors.

Use. As an ornamental stone.

Anorthite

Composition. Calcium-aluminum silicate, CaAl2Si208 Sil ica 43.2, alumina 36.7, lime 20.1. Soda is usually present, in small amount, in the albite molecule, NaAlSuOs.

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Crystallization. Triclinic. Crystals usually prismatic paral lel to vertical axis. Twinning common according to albite and pericline laws (see above).

Structure. Massive cleavable. Crystals rare.

Physical Properties. Cleavage in two directions at 85° 50'. One cleavage (parallel to base) better than the other. H. 6. G. 2.75. Vitreous to pearly luster. Color white, grayish, reddish. Transparent to opaque.

Tests. Fusible at 4.5. Dissolves slowly in hydrochloric acid and yields a silica jelly upon evaporation. Gives a strong test for calcium (see under oligoclase) and only a slight yellow flame (sodium).

Occurrence. A rock-making mineral, particularly in the darkcolored basic igneous rocks. Associated with various calcium and magnesium silicates. Occurs in andesite, basalt, diorite, gabbro, norite, etc.; in chrysolite-bearing rocks, in amphibolites. Also in druses of ejected volcanic blocks and in the granular limestone of contact deposits. Found in the lavas of Mount Vesuvius; of Japan, etc.

Name. Derived from the Greek word meaning oblique, be cause of its triclinic crystallization.

Composition. A

2. METASILICATES Leucite

metasilicate of aluminum and potassium, Silica 55.0, alumina 23.5, potash 21.5.

Crystallization. Isometric. Trapezohedral habit (Fig. 302). Other forms rare. Strictly isometric only at temperatures of 500° C. or over. On cooling below this temperature it undergoes an internal molecular rearrangement to that of some other crystal system, but the external form does not change. It is formed in lavas at high temperatures and is then isometric in internal struc ture as well as outward form.

Enstatite, Bronzite, Hypersthene 245

Structure. Usually in distinct crystals, also in disseminated grains.

Physical Properties. H. 5.5-6. G. 2.5. Vitreous to dull luster. Color white to gray. Translucent to opaque.

Tests. Infusible. Decomposed by hydrochloric acid with the separation of silica but without the formation of a jelly. Addition of ammonia to the solution gives precipitate of aluminum hydroxide. When mixed with powdered gypsum and fused gives violet potas sium flame (best observed through a blue glass).

Occurrence. A rather rare mineral, occurring only in igneous rocks, and especially in the recent lavas, being rarely observed in deep-seated rocks. Found in rocks in which the amount of potassium in the magma was in excess of the amount necessary to form feldspar. Is not observed, therefore, in rocks that show quartz. Chiefly found in the rocks of central Italy; notably as phenocrysts in the lavas of Vesuvius. Pseudomorphs after leucite are found in syenites of Arkansas, Montana, Brazil, etc.

Name. From a Greek word meaning white.

PoUudte, is a rare mineral that belongs in the same group as leucite.

Pyroxene Group

The Pyroxene Group includes a series of related metasilicates which have calcium, magnesium and ferrous iron as the important bases, also manganese and zinc. Further certain molecules con tain the alkalies and aluminum and ferric iron. They may belong to either the orthorhombic, monoclinic or triclinic systems, but the crystals of the different species are closely similar in many respects.

ORTHORHOMBIC SECTION Enstatite, Bronzite, Hypersthene

A group of orthorhombic members of the pyroxene group, en statite being magnesium metasilicate, MgSi03; bronzite, the same as enstatite, with small amounts of iron replacing the magnesium; hypersthene, an iron-magnesium metasilicate, Dis tinct crystals rare. Usually foliated massive with good cleavage;

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fibrous, etc. Color from white in enstatite to green and brown with increase in iron. Rock-making minerals, occurring like the mono clinic pyroxenes but much rarer. Found in basic igneous rocks, such as peridotite, gabbro, etc.

Pyroxene

Composition. Pyroxene is a metasilicate, varying in its com position. It contains as bases chiefly calcium and magnesium, with smaller amounts of ferrous iron. In some varieties, however, molecules are introduced in which are the alkalies (chiefly sodium), aluminum and ferric iron. The more important varieties of pyrox ene with the formulas assigned to them follow.

Diopside,

Common pyroxene,

Augite, with MgAl2Si06 and NaAlSi206; with iron isomorphous with both the magnesium and the aluminum.

Fig. 304.

Fig. 303.

Fig. 305.

These varieties form an isomorphous series, and all gradations between them appear. Other varieties of less common occurrence are hedenbergite, schefferite, a manganese pyroxene; jeffersonite, a manganese-zinc pyroxene.

Crystallization. Monoclinic. Crystals prismatic in habit; prism faces make angles of 87° and 93° with each other. The prism zone commonly shows the prism faces truncated by the faces of both vertical pinacoids, so that the crystals show, when viewed

Pyroxene

parallel to the vertical axis, a rectangular cross section with trun cated corners. The interfacial angles in the prism zone are either exactly or very closely 90° and 45°. The terminations vary, being made up frequently of a combination of the basal plane with pyra mids both in front and behind (Figs. 303-305).

Structure. In crystals. Often lamellar. Coarse to fine gran ular.

Physical Properties. Prismatic cleavage sometimes good, often interrupted. Sometimes basal parting observed, often shown by twinning lamella; (see Fig. A, pi. X). H. 5-6. G. 3. 2-3.6. Vitreous luster. Color varying from white and light green in diopside, to green in pyroxene, through dark green to black in augite. Color deepens with increase in the amount of iron present. Transparent to opaque.

Tests. Fusible from 4 to 4.5. Insoluble in hydrochloric acid. To test for bases: fuse with sodium carbonate; dissolve in nitric acid; evaporate to dryness; notice the formation of silica jelly; moisten residue with water and hydrochloric acid; boil and filter from insoluble silica; add ammonium hydroxide in excess, precipi tate of aluminum and ferric hydroxide; to boiling filtrate add ammonium oxalate, precipitate of calcium oxalate; to filtrate add sodium phosphate, precipitate of ammonium magnesium phos phate. Recognized usually by its characteristic crystals.

Occurrence. The pyroxenes are common and important rock making minerals, being found chiefly in the dark colored igneous rocks, especially those whose magmas were rich in iron, calcium and magnesium. They are seldom to be found in rocks that contain much quartz. Augite is found in basaltic lavas, and in the dark colored intrusions known generally as trap, in gabbros and peridotites. Diopside and common pyroxene are found sometimes in syenites and similar rocks; also as metamorphic minerals in impure recrystallized dolomitic limestones. Common pyroxene also occurs in some gneisses. In the limestones, pyroxene is often associated with tremolite, scapolite, vesuvianite, garnet, titanite, phlogopite, etc. In igneous rocks it is found with orthoclase, the plagioclase feldspars, nephelite, chrysolite, leucite, amphibole, magnetite, etc. Some of the notable localities, particularly for fine crystals, are the following: For diopside, Ala and Traversella in Piedmont; Nordinark, Sweden; in various localities in Orange County, New York; for

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augite, in the lavas of Vesuvius; at Val di Fassa, Trentino, Italy; Bilin, Bohemia; hedenbergite from Sweden; schefferite from Sweden; jeffersonite from Franklin, New Jersey.

Names. The name pyroxene, stranger to fire, is a misnomer, and was given to the mineral because it was thought that it did not occur in igneous rocks. Diopside comes from two Greek words meaning double appearance. Augite comes from a Greek word meaning luster.

Use. Clear green diopside or common pyroxene is occasionally used as a gem material.

jEgirite or Acmite

A soda-ferric iron pyroxene, Monoclinic. Slender prismatic crystals, often with steep terminations. Faces often im perfect. Imperfect prismatic cleavage with 93° angle. H. 6-6.5. G. 3.5-3.55. Vitreous luster. Color brown or green. Trans lucent to opaque. Fusible at 3.5, giving yellow sodium flame. Fused globule slightly magnetic. A comparatively rare rock-mak ing mineral found chiefly in rocks containing leucite or nephelite, as nephelite-syenite and phonolite.

Spodumene

Composition. Lithium-aluminum metasilicate, Silica 64.5, alumina 27.4, lithia 8.4. Usually has a small amount of sodium replacing the lithium.

Crystallization. Monoclinic. Prismatic crystals, flattened frequently parallel to the orthopinacoid. Deeply striated ver tically (see Fig. B, pi. X). Crystals usually coarse and with roughened faces. Sometimes very large.

Structure. In crystals or cleavable masses.

Physical Properties. Perfect prismatic cleavage. H. 6.5- 7. G. 3.18. Vitreous luster. Color white, gray, pink, yel low, green. Transparent to translucent when unaltered.

Tests. Fusible at 3.5, throwing out fine branches at first, and then fusing to a clear glass. Gives a crimson flame (lithium). Insoluble in acids.

Plate X.

A,

B.

A. Pyroxene showing Twinning Lamella; due to Basal Parting. B Spodumene Crystal from Huntington, Massachusetts C. Garnet Crystals in Mica-Schist.

Jadeite

Varieties. Ordinary. Color white or gray, sometimes pink. Commonly in flattened prismatic crystals, often very large. Frequently altered to other minerals.

Hiddenite. A clear, transparent variety ranging in color from yellow-green to deep emerald. Found in small striated and etched crystals.

Kunzite. A transparent variety ranging from pale pink to deep amethystine purple. Has been found in flattened crystals 8 to 10 inches in length, 5 to 6 in breadth.

Alteration. Spodumene very easily alters to other species, becoming dull and opaque. The alteration products include albite, eucryptite (LiAlSi04), muscovite, microcline.

Occurrence . A comparatively rare species, but found occasionally in very large crystals in pegmatite veins. Occurs in Goshen, Chester field, Huntington and Sterling, Massachusetts; Branchville, Con necticut; Etta tin mine, Pennington County, South Dakota, in crystals measuring many feet in length. Hiddenite occurs with emerald beryl at Stony Point, Alexander County, North Carolina. Kunzite is found with pink beryl in San Diego County, California. Occurs at various localities in Madagascar.

Names. Spodumene comes from a Greek word meaning ash colored. Hiddenite is named for Mr. W. E. Hidden; kunzite for Dr. G. F. Kunz.

Use. The varieties hiddenite and kunzite furnish very beauti ful gem stones but are limited in their occurrence.

Jadeite

A sodium-aluminum metasilicate, Massive, gran ular to closely compact. H. 6.5-7. G. 3.33-3.35. Vitreous luster. Color white, gray to light green. Translucent to opaque. Very tough. Fuses at 2.5, coloring the flame yellow (sodium). Forms in part the material known as jade and highly prized by oriental peoples as an ornamental material. Made into finely carved ornaments and utensils, and when of fine color and translucent com mands a high price. Found chiefly in Upper Burma, in southern China and in Tibet.

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Wollastonite

Composition. Calcium metasilicate, CaSi03 Silica 51.7, lime 48.3.

Crystallization. Monoclinic. Usually in tabular crystals, with either base or orthopinacoid prominent.

Structure. Commonly massive, cleavable to fibrous; also compact.

Physical Properties. Perfect cleavage parallel to orthopina coid. H. 5-5.5. G. 2. 8-2. 9. Vitreous luster, pearly on cleavage surfaces. Sometimes silky when fibrous. Colorless, white or gray. Translucent to opaque.

Tests. Fusible at 4 to a white, almost glassy globule. De composed by hydrochloric acid, with the separation of silica but without the formation of a j elly . Filtered solution with ammonium hydroxide and ammonium carbonate gives white precipitate of calcium carbonate.

Occurrence. Occurs chiefly as a contact mineral in crystalline limestones, formed by the action of silicic acid on the limestone, commonly in the presence of mineralizers and at a comparatively low temperature. Associated with calcite, diopside, lime garnet, tremolite, lime feldspars, vesuvianite, epidote, etc. May at times be so plentiful as to constitute the chief mineral of the rock mass. Such wollastonite rocks are found in California, the Black Forest, Brittany, etc. The crystallized mineral is found at Csiklova in Rumania; at Vesuvius; from Chiapas, Mexico. At Diana, Lewis Co., and also in Orange and St. Lawrence Counties, New York.

Pectolite

Composition. Silica 54.1, lime 33.8, soda 9.3, water 2.7.

Crystallization. Monoclinic. Crystals usually elongated parallel to the ortho-axis.

Structure. Usually in aggregates of acicular crystals. Fre quently radiating, with fibrous appearance. Sometimes compact.

Physical Properties. Perfect cleavage parallel to the ortho pinacoid. H. 5. G. 2. 7-2. 8. Vitreous to pearly luster. Colorless, white or gray.

Rhodonite

Tests. Fuses quietly at 2.5-3 to a glass; colors flame yellow (sodium). Decomposed by hydrochloric acid, with the separa tion of silica but without the formation of a jelly. Filtered solu tion with ammonium hydroxide and ammonium carbonate gives white precipitate of calcium carbonate. Water in C. T.

Occurrence. A mineral of secondary origin similar in its occur rence to the zeolites. Found lining amygdaloidal cavities in basalt, associated with various zeolites, phrenite, calcite, etc. Found at Bergen Hill and West Paterson, New Jersey.

Triclinic Section

Rhodonite

Composition. Manganese metasilicate, MnSi03 Silica 45.9, manganese protoxide 54.1. Iron, calcium and sometimes zinc replace a part of the manganese.

Crystallization. Triclinic. Crystals commonly tabular paral lel to base (Fig. 306). Crystals often rough with rounded edges.

Structure. Commonly massive, cleavable to compact; in embedded grains.

Physical Properties. Prismatic cleav age at about 92°. H. 6-6.5. G. 3.63.

Vitreous luster. Color rose-red, pink, brown.

Translucent to opaque.

Tests. Fusible (3-3.5) to a nearly black glass. Insoluble in hydrochloric acid. In O. F. gives clear reddish violet color to borax bead.

Fig. 306. Franklin Fur nace, New Jersey.

Occurrence. Found at Langban, Sweden, with iron ore; found in large masses near Ekaterinburg, Urals; from Broken Hill, New South Wales. A zinciferous variety, known as fowlerite, occurs in good-sized crystals in limestone with franklinite, willemite, zincite, etc., at Franklin Furnace, New Jersey.

Name. Derived from the Greek word for a rose, in allusion to the color.

Use. Sometimes polished for use as an ornamental stone. Obtained chiefly from the Urals.

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Amphibole Group

The minerals of the Amphibole Group crystallize in either the orthorhombic, monoclinic or triclimc systems, but the crystals of the different species are closely similar in many respects. Chem ically they form a series parallel to that of the Pyroxene Group (page 245), being metasilicates with calcium, magnesium and fer rous iron as important bases, and also with manganese and the alkalies. Certain molecules that are present in some varieties contain aluminum and ferric iron.

Orthorhombic Section

Anthopyllite

An orthorhombic amphibole, corresponding to the orthorhombic pyroxene group, enstatite — bronzite - hypersthene. An ironmagnesium metasilicate, Rarely in distinct crystals. Commonly lamellar or fibrous. Perfect prismatic cleavage. Color gray to various shades of green and brown. A comparatively rare mineral, occurring in the crystalline schists and thought to have been derived from the metamorphism of chrysolite.

Amphibole

Composition. The amphiboles consist of a series of minerals analogous in many ways to the pyroxenes. They are chiefly metasilicates of calcium and magnesium with ferrous iron replacing the magnesium. Other molecules are at tunes introduced, in which are the alkalies, aluminum and ferric iron. The more important varieties of amphibole with the formulas assigned to them follow.

V Tremolite ,

J Hornblende, with and Mg2Al,- Ferrous iron is isomorphous with the magnesium and ferric iron with the aluminum.

These varieties form an isomorphous series and all gradations between them occur.

Amphibole

Crystallization. Monoclinic. Crystals prismatic in habit; the prism faces make angles of 55° and 125° with each other (com pare the 87° and 93° angles of pyroxene). The prism zone shows, in addition to the prism faces, usually those of the clinopinacoid and sometimes also those of the orthopinacoid. Prism zone fre quently vertically striated and imperfectly developed. When the prism faces are distinct, the cross section of the crystal, when viewed in a direction parallel to the vertical axis, does not have the rectangular shape shown by the crystals of pyroxene. The termination of the crystals is almost always formed by the two faces of a low clinodome (Figs. 307 and 308).

Fig. 307.

Fig. 308.

Structure. In crystals. Often bladed and frequently in radi ating columnar aggregates. Sometimes in silky fibers. Coarse to fine granular. Compact.

Physical Properties. Perfect prismatic cleavage at angle of 125°, often yielding a splintery surface. H. 5-6. G. 3-3.3. Vitreous luster. Often with silky sheen in the prism zone. Color varying from white and light green in tremolite, to green in actinolite, through dark green to black in hornblende. Color deepens with increase in the amount of iron present. Transparent to opaque.

Tests. Fusible 3-4. Chemical tests same as for pyroxene, which see. Told from pyroxene by its better prismatic cleavage, by the difference in the prismatic angle and by the characteristic presence on the crystals of the low clinodome.

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Occurrence. Amphibole is an important and widely distributed rock-making mineral, occurring both in igneous and metamorphic rocks, being particularly characteristic, however, of the latter. The fact that amphibole frequently contains hydroxyl and fluorine in dicates that, in some degree, it is often of pneumatolytic origin. Tremolite is most frequently found in impure, crystalline, dolomitic limestones, where it has been formed during the crystallization of the rock, while undergoing metamorphism. Actinolite commonly occurs in the crystalline schists, being often the chief constituent of green-colored hornblende schists and greenstones. Frequently the amphibole of such rocks has had its origin in the pyroxene contained in the igneous rock from which the metamorphic type has been derived. Common hornblende is found in igneous rocks, such as granites, syenites, diorites, gabbros, and in some peridotites; it rarely occurs in the dark traps and basalts. It also occurs in the metamorphic rocks, such as gneisses and hornblende schists.

Notable localities for the occurrence of crystals are: tremolite from Campolungo, Ticino; in the Tyrol; in Piedmont, Italy; from Russell, Gouverneur, Amity, Pierrepont, DeKalb, etc., New York; actinolite from Greiner, Zillerthal, Tyrol; hornblende from Bilin, Bohemia; Monte Somma, Italy. Actinolite frequently comes fibrous, and is the material to which the name asbestos was originally given. Has been found in the metamorphic rocks in various states along the Appalachian Mountains. Nephrite is a tough, compact variety of actinolite which supplies much of the material known as jade (see also under jadeite). A famous locality for its occurrence is in the Kuen Lun Mountains, on the southern border of Turkestan.

Names. Tremolite is derived from the Tremola Valley near St. Gothard. Actinolite comes from two Greek words meaning a ray and stone, in allusion to its frequently somewhat radiated structure.

Uses. The fibrous variety is used to some extent as asbestos material. The fibrous variety of serpentine furnishes more and usually a better grade of asbestos. The compact variety, nephrite, is used largely for ornamental material by oriental peoples and is called jade.

Among the other rarer monoclinic members of the Amphibole Group are glaucophane, riebeckite, crocidolite, arfvedsonite,

Beryl

Triclinic Section

The only member of the Triclinic Section of the Amphibole Group is the rare mineral cenigmatite,

Beryl

Composition. BesAhSieOis. Analyses show a small amount of w7ater. Small amounts of the alkali oxides, often in part con sisting of caesium oxide, frequently replace the beryllium oxide.

Crystallization. fffYngnrtfll ..iStrnnf -prismatic-habit. Fre quently vertically striated and grooved. Forms usually present consist only of prism of first order and base (Fig. 309). Small

n

m

m

Fig. 309.

Fig. 310.

pyramid faces of both the first and second orders sometimes occur, but the pyramid faces are rarely prominent (Fig. 310). Dihexagonal forms quite rare. Crystals frequently of consider able size with rough faces.

Structure. In crystals. Also massive, with indistinct colum nar structure or granular.

Physical Properties. H. 7.5-8. G. 2.75-2.8. Vitreous luster. Color commonly bluish green or light yellow; may be deep emerald-green, golden-yellow, pink, white or colorless. Transparent to subtranslucent. Frequently the larger, coarser crystals show a mottled appearance due to the alternation of clear transparent spots with cloudy, almost opaque portions.

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Tests. B. B. whitens and fuses with difficulty at 5-5.5 to an enamel. Yields a little water on intense ignition. Insoluble in acids. Recognized usually by its hexagonal crystals, its hardness, color, etc.

Varieties. Ordinary Beryl. In coarse translucent to opaque crystals or masses, usually of a pale greenish blue or yellow color. Sometimes in veiy large crystals; one from Grafton, New Hamp shire, measured over 4 feet in length with a diameter between 20 and 30 inches, weight 2900 pounds.

Aquamarine. Name given to the pale greenish blue transparent stone. Used as a gem.

Golden Beryl. A deep golden-yellow variety, which, when clear, is used as a gem.

Rose Beryl. A variety varying in color from pale pink to deep rose. Beautiful gem material from Madagascar has been named morganite.

Emerald. The true emerald is the deep green transparent beryl and is among the most highly prized of gems. The color is due to small amounts of chromium.

Occurrence. Beryl, although containing the rare element beryl lium, is a rather common and widely distributed mineral. It occurs usually in granite rocks, either in druses or in pegmatite veins. It is also found in mica-schist and in connection with tin ores. Emeralds of gem quality occur in a dark bituminous limestone at Muso, 75 miles northwest of Bogota, Colombia. This locality has been worked almost continually since the middle of the sixteenth century, and has furnished the greater part of the emeralds of the world. Another famous locality for emeralds is in Siberia on the river Takowaja, 45 miles east of Ekaterinburg. They occur in a mica-schist asso ciated with phenacite, chrysoberyl, rutile, etc. Rather pale emeralds have been found in small amount from Alexander County, North Carolina, associated with the green variety of spodumene, hiddenite. Beryl of the lighter aquamarine color is much more common, and is found in gem quality in Brazil, Siberia, and many other localities. From the pegmatites of Madagascar. In the United States they have been found in various places in Maine, New Hampshire, Massachu setts, Connecticut, North Carolina, Colorado, etc. The golden beryl has been found in Maine, Connecticut, North Carolina and Pennsylvania; also in Siberia and Ceylon. The rose-colored beryl has been found in San Diego County, California, associated with pink

Nephelite

tourmaline and the pink spodumene, kunzite. A similar occurrence in Madagascar has furnished magnificent rose-colored stones (morganite).

Use. Used as a gem stone of various colors. The emerald ranks as one of the most valuable of stones, at times being of much greater value than the diamond.

Iolite. Cordierite

A complex silicate of magnesium, ferrous iron and aluminum. Orthorhombic. Usually in short pseudohexagonal twinned crystals; as embedded grains; massive. Vitreous luster. Color different shades of blue. Most commonly altered into some form of mica, becoming opaque and of various shades of grayish green. Found as an accessory mineral in granite, gneiss (cordierite gneiss), schists, and in contact metamorphic zones.

3. Orthosilicates

N ephelite

Composition. Sodium-aluminum silicate, approximately NaAlSiOi. There is always a few per cent of potash present, sometimes also lime, replacing the soda.

Crystallization. Hexagonal. Rarely in small prismatic crys tals with basal plane; sometimes shows pyramidal planes.

Structure. Almost invariably massive, compact, and in em bedded grains. Massive variety often called elceolite.

Physical Properties. Distinct cleavage parallel to prism. H. 5.5-6. G. 2.55-2.65. Vitreous luster in the clear crys tals to greasy luster in the massive variety. Colorless, white or yellowish. In the massive variety gray, greenish and reddish. Transparent to opaque.

Tests. Fusible at 4 to a colorless glass. B. B. gives strong yellow flame of sodium. Readily soluble in hydrochloric acid and on evaporation yields a silica jelly.

Alteration. Easily alters into various other minerals, such as the zeolites, natrolite, analcite, hydronephelite, thomsonite; also sodalite, muscovite, kaolin, etc.

Manual Of Mineralogy

Occurrence. Nephelite is rarely found except in igneous rocks.

It occurs in some recent lavas as glassy crystals, such as are found in the lavas of Vesuvius. The opaque, massive or coarsely crystal line variety is found in the older rocks and is called elseolite. Phonolite, nephelite-syenite and nephelite-basalt are important rocks in wliich nephelite is an essential constituent. It is only to be found in rocks whose magmas contained an excess of soda over the amount required to form feldspar. It is therefore seldom found in rocks that contain free quartz. Extensive masses of nephelite rocks, nephelite-syenites, are found in Norway. In crystals in the lavas of Vesuvius. Massive and crystallized nephelite is found at Litchfield, Maine, associated with cancrinite. Found near Magnet Cove, Arkansas.

Name. Nephelite is derived from a Greek word meaning a cloud, because when immersed in acid the mineral becomes cloudy. Elceolite is derived from the Greek word for oil, in allusion to its greasy luster.

Cancrinite, is a rare mineral similar to nephelite in occurrence and associations.

Sodalite Group

Sodalite

Composition, Isqgietric. Crystals rare, usually dodecahedrons. Commonly massive, in embedded grains. Dodecahedral cleavage. H. 5.5-6. G. 2.15-2.3. Vitreous luster. Color usually blue, also white, gray, green. Transparent to opaque. Fusible at 3.5, to a colorless glass, giving a strong yellow flame (sodium). Soluble in hydrochloric acid and gives gelatinous silica upon evaporation. Nitric acid solution with silver nitrate gives white precipitate of silver chloride. A comparatively rare rock-making mineral associated with nephelite, cancrinite, etc., in nephelite-syenites, trachytes, phonolites, etc. Found in transpar ent crystals in the lavas of Vesuvius. The massive blue variety is found at Litchfield, Maine; in Ontario and Quebec; near Kicking Horse Pass, British Columbia. Similar minerals, but rarer in . their occurrence, are hauynile, and noselite,

Lazurite. Lapis-lazuli

Composition, with small amounts of the sodalite and haiiynite molecules in isomorphous replacement. Iso metric. Crystals rare, usually dodecahedral. Commonly massive,

Garnet Group

compact. H. 5-5.5. G. 2.4-2.45. Vitreous luster. Color deep azure-blue, greenish blue. Translucent. Fusible at 3.5, giv ing strong yellow flame (sodium). Soluble in hydrochloric acid with slight evolution of hydrogen sulphide gas, and gives gelatinous silica upon evaporation. A rare mineral, occurring usually in crys talline limestones as a product of contact metamorphism. Lapislazuli is usually a mixture of lazurite with small amounts of calcite, pyroxene, etc. It commonly contains small disseminated particles of pyrite. It is used as an ornamental stone, for carvings, etc. The best quality of lapis-lazuli comes from northeastern Afghanistan. Also found at Lake Baikal, Siberia, and in Chile.

Garnet Group

Composition. The garnets are orthosilicates which conform to the general formula Rs'TV'SiCh. R" may be calcium, magnesium, ferrous iron and manganese; R'" may be aluminum, ferric iron and chromium. The formulas of the chief varieties are given below; many of them, however, grade more or less into each other.

Grossularite,

Pyrojie,

Almandite,

Spessartite,

Andradite,

Uvarovite,

Crystallization. Isometric. Common forms dodecahedron (Fig. 311) and trapezohedron (Fig. 312), often in combination (Figs. 313 and 314). Hexoctahedron observed at times (Fig. 315). Other forms rare.

Structure. Usually distinctly crystallized; also in rounded grains; massive granular, coarse or fine.

Physical Properties. H. 6.5-7.5. G. 3.15-4.3, varying with the composition. Luster vitreous to resinous. Color vary ing with composition; most commonly red, also brown, yellow, white, green, black. White streak. Transparent to almost opaque.

Tests. With the exception of uvarovite, all garnets fuse at 3 to 3.5; uvarovite is almost infusible. The iron garnets, almandite

Manual Of Mineralogy

and andradite, fuse to magnetic globules. Spessartite when fused with sodium carbonate gives a bluish green bead (manga nese). Uvarovite gives a green color to salt of phosphorus bead (chromium). Andradite is somewhat difficultly soluble in hydro chloric acid and gelatinizes imperfectly on evaporation. All the

other garnets are practically insoluble in acids. All of them, with the exception of uvarovite, may be dissolved in hydrochloric acid after simple fusion and the solutions will gelatinize on evaporation. Garnets are usually recognized by their characteristic isometric crystals, their hardness, color, etc. It frequently requires an analysis to positively distinguish between the different members of the group.

Varieties. Grossularite, Essonite, Cinnamon Stone. Calciumaluminum garnet. Often contains ferrous iron replacing cal cium and ferric iron replacing aluminum. Color white, green,

Garnet Group

yellow, cinnamon-brown, pale red. Name derived from the botanical name for gooseberry, in allusion to the light green color of the original grossularite.

Pyrope. Precious garnet in part. Magnesium-aluminum gar net. Calcium and iron also present. Color deep red to nearly black. Often transparent and then used as a gem. Name de rived from Greek, meaning firelike. Rhodolite is name given to a pale rose-red or purple garnet, corresponding in composition to two parts of pyrope and one of almandite.

Almandite. Precious garnet in part. Common garnet in part. Iron-aluminum garnet. Ferric iron replaces aluminum and mag nesium replaces ferrous iron. Color fine deep red, transparent in precious garnet; brownish red, translucent to opaque in common garnet. Name derived from Alabanda, where in ancient times garnets were cut and polished.

Spessartite. Manganese-aluminum garnet. Ferrous iron re places the manganese and ferric iron the aluminum. Color brownish to garnet-red.

Andradite. Common garnet in part. Calcium-iron garnet. Aluminum replaces the ferric iron; ferrous iron, manganese and sometimes magnesium replace the calcium. Color various shades of yellow, green, brown to black. Named after the Portuguese mineralogist, d'Andrada.

Uvarovite. Calcium-chromium garnet. Color emerald-green. Named after Count Uvarov.

Occurrence. Garnet is a common and widely distributed min eral, occurring as an accessory constituent, nf Vnetnornhic and sometimes of igneous rocks. Its most characteristic occurrence is in miea-ttetLiat (w FiB p] , X). hornblende schists and gneisses. Found in pegmatite veins,' more rarely in granite rocks. Grossu larite' is found chiefly as a product of contact or regional metamor phism in crystalline limestones. Almandite is especially characteris tic of the mica-schists. Pyrope is often found in peridotite rocks and the serpentines derived from them. Spessartite occurs in the igneous rock, rhyolite. Melanite, a black variety of andradite, occurs mostly in certain eruptive rocks. Uvarovite is found in serpentine associated with chromite. Garnet frequently occurs as rounded grains in stream- and sea-sands.

Manual Of Mineralogy

AJmandite, of gem quality, is found in northern India, Ceylon, Brazil, etc. Fine crystals, although for the most part too opaque for cutting, are found in a mica-schist on the Stikine River, Alaska. Pyrope of gem quality is found associated with clear grains of chrys olite (peridot) in the surface sands near Fort Defiance, close to the Utah-Arizona state line. Famous localities for pyrope gems are near Meronitz, Bohemia. Grossularite is only a little used in jewelry, but essonite or cinnamon stones of good size and color are found in Cey lon. A green andradite, known as demantoid, comes from the Urals and yields fine gems known as Urcdian emeralds.

Alteration. Garnet often alters to other minerals, particularly talc, serpentine and chlorite.

Name. Garnet is derived from the Latin granatus, meaning like a grain. Carbuncle, an old name for garnet and other red stones, was derived from the Latin word carbo, coal, and is used at present to designate garnets cut in oval form.

Use. Chiefly as a rather inexpensive gem stone. Sometimes ground and used on account of its hardness for abrading purposes, as sand for sawing and grinding stone, or for making sandpaper.

Chrysolite Group

Chrysolite or Olivine. Peridot

Composition. Orthosilicate of magnesium, with varying amounts of ferrous iron, The ratio between the magnesium and iron varies widely.

Crystallization. Orthorhombic. Crystals usually a combi nation of prism, macro- and brachypinacoids and domes, pyramid and base. Often flattened parallel to either the macro- or brachypinacoid.

Structure. Usually in embedded grains or in granular masses.

Physical Properties. H. 6.5-7. G. 3.27-3.37. Vitre ous luster. Olive to grayish green, brown. Transparent to translucent.

Tests. Infusible. Rather slowly soluble in hydrochloric acid and yields gelatinous silica upon evaporation. After evaporation to dryness, take up residue in water with nitric acid, filter off

Chrysolite Or Olivine

silica, add ammonia in excess to precipitate ferric hydroxide, filter, add ammonium oxalate to prove absence of calcium, add sodium phosphate and obtain precipitate of ammonium-magnesium phos phate (test for magnesium). Distinguished usually by its glassy luster, green color and granular structure.

Occurrence. A rather common rock-making mineral, varying from an accessory character to that of a main constituent of the rock. It is found principally in the dark colored ferro-magnesium igneous rocks such as gabbro, peridotite and basalt. A rock, known as dunite, is made up almost wholly of chrysolite. Found also at times as glassy grains in meteorites. Occasionally in crystalline dolomitic limestones. Associated often with pyroxene, the plagioclase feld spars, magnetite, corundum, chromite, serpentine, etc. The trans parent green variety, known as peridot, and used as a gem material, was found in ancient times in the East, the exact locality for the stones not being known. At present peridot is found in Upper Egypt, near the Red Sea, and in rounded grains associated with pyrope garnet in the surface gravels of Arizona and New Mexico. Crystals of chrysolite are found in the lavas of Vesuvius. Larger crystals, altered to serpentine, come from Snarum, Norway. Chryso lite occurs in granular masses in the volcanic bombs in the Eifel. Dunite rocks are found at Dun Mountain, New Zealand, and with the corundum deposits of North Carolina.

Alteration. Very readily altered to serpentine; magnesium carbonate, iron ore, etc., may form at the same time.

Name. Chrysolite means golden stone. Olivine derives its name from the usual olive-green color of the mineral, and is the term usually given to the species when speaking of it as a rock making mineral. Peridot is an old name for the species.

Use. As the clear green variety, known usually as peridot, it has some use as a gem.

Other members of the Chrysolite Group which are rarer in oc currence arc monticellite, CaMgSiO.,; fosterite, Mg2Si04 ; and fayalite, Fe2Si04. Ordinarily chrysolite is intermediate in com position between the last two. Another member which has been found in the zinc deposits at Franklin Furnace, New Jersey, is tephroite, Mn2Si04.

Manual Of Mineralogy

PHENACITE GROUP Willemite

Composition. Zinc orthosilicate, Zn2Si04 Silica 27, zinc oxide 73; zinc 58.6. Manganese often replaces a considerable part of the zinc (manganiferous variety called troostite), iron also present at times in small amount.

Crystallization. Hexagon nl-rhombohedral : tri-rhombohedral. In hexagonal prisms with rhombohedral terminations. Faces of third-order rhombohedrons rare.

Structure. Usually massive to granular. Rarely crystallized except in variety troostite.

Physical Properties. H. 5.5. G. 3.89-4.18. Vitreous to resinous luster. Color white, yellow-green, blue, when pure; with increase of manganese becomes apple-green, flesh-red and brown. Transparent to opaque.

Tests. Willemite infusible, troostite difficultly fusible (4.5-5). Soluble in hydrochloric acid and yields gelatinous silica on evapo ration. Gives a coating of zinc oxide when heated with sodium carbonate on charcoal; coating yellow when hot, white when cold; if coating is moistened with cobalt nitrate and heated again it turns green. Troostite will give reddish violet color to the borax bead in 0. F. (manganese).

Varieties. Ordinanj. White or light colored.

Troostite. Apple-green, flesh-red or gray color. Contains a considerable amount of manganese. Found at Franklin Fur nace, New Jersey, in quite large crystals.

Occurrence. Found at Altenberg, near Moresnet, Belgium, and at Franklin Furnace, New Jersey. At the latter locality it is asso ciated with franklinite and zincite, often in an intimate mixture; also embedded in calcite. Also from Algeria, French Congo, North ern Rhodesia, South West Africa, Greenland. Occurs sparingly at Merritt Mine, New Mexico.

Use. A valuable zinc ore.

W Erne Rite

Phenacite

Beryllium orthosilicate, Hexagonal-rhombohedral; trirhombohedral. Crystals usually rhombohedral in form, sometimes with short prisms. Often with complex development and fre quently showing the faces of the third-order rhombohedron. Pris matic cleavage. H. 7.5-8. G. 2.96. Vitreous luster. Color less, white. Transparent to translucent. Infusible and insoluble. A rare mineral, found commonly in pegmatites as a pneumatolytic mineral, associated with topaz, chrysoberyl, beryl, apatite, etc. Fine crystals are found at the emerald mines in the Urals, at Pike's Peak and Mount Antero, Colorado, and in Minas Geraes, Brazil. Occasionally cut as a gem stone.

Dioptase, H2CuSi04, is a rare mineral belonging in this group.

Scapolite Group

A group of minerals varying in composition by the isomorphous mixture in different amounts of the two molecules, Ca4Al6- SUOv,(Me) and Na4Al3Si9024Cl,(Ma). When the first molecule (Me) alone is present, the surname of meionite is used; when the second molecule ( Ma ) represents the composition, the name marialite is used. Wemerile, or common scapolite, shows a com bination of the two molecules according to the ratios of Me: Ma as 3 : 1 to 1 : 2; while mizzonite corresponds to the ratios of Me : Ma as 1 : 2 to 1 : 3. Mixtures in all proportions may exist.

Wernerite. Common Scanolite

Composition. See above.

Crystallization. .gQnn.l- tripyramidal. Crystals usually prismatic. Prominent forms are prisms of the first and second orders, pyramid of first (Fig. 316). Rarely shows the faces of the pyramid of the third order (Fig. 317).

Structure. Crystals are usually coarse, with rough faces and often large. Also massive, granular, or with faint fibrous appear ance.

Physical Properties. Imperfect prismatic cleavage. H. 5-6. G. 2.68. Vitreous luster when fresh and unaltered. Color white, gray or pale green. Transparent to opaque.

Manual Of Mineralogy

Tests. Fusible. Varieties containing sodium give yellow flame on ignition. Imperfectly decomposed by hydrochloric acid, yielding separated silica but without the formation of a jelly.

Alteration. Easily altered into various other minerals, such as mica, epidote, talc, kaolin, etc.

Fig. 317.

Occurrence. The scapolites occur in the crystalline schists, gneisses and amphibolites, and in many cases have probably been derived by alteration from plagioclase feldspars. They also charac teristically occur in crystalline limestones formed through the con tact metamorphic action of an intruded igneous rock. Associated with light colored pyroxene, amphibole, garnet, apatite, titanite, zircon, etc. . Crystals of gem quality with a yellow color occur in Madagascar. Found in various places in Massachusetts; Orange, Lewis, and St. Lawrence counties, New York; at various points in Ontario, Canada.

The other members of the group, meionite, mizzonite and marialite, are much rarer in occurrence. Their crystals are usually smaller and of better quality than those of wernerite. Meionite and missonite are found in limestone blocks on Monte Somma.

Vesuvianite

Composition. A basic silicate of calcium and aluminum. Contains usually also iron oxides, magnesia and fluorine. For mula uncertain.

Vesuvianite

Crystallization. Tetragonal. Prismatic in habit. Often ver tically striated. Common forms are prisms of first and second orders, pyramid of first order and base (Figs. 318 and 319). Some crystals show a more complex development with other prisms, pyramids, ditetragonal forms, etc.

Structure. In crystals, also massive, columnar, granular.

Pig. 318.

Physical Properties. H. 6.5. G. 3.35-4.45. Vitreous to resinous luster. Usually green or brown in color; also yellow, blue, red. Commonly subtransparent to translucent. Streak white.

Tests. Fuses with intumescence to a greenish or brownish glass. Only slightly soluble in acids but gelatinizes in hydro chloric acid after simple fusion.

Occurrence. Usually to be found in crystalline .limestones where they have been metamorphosed by the contact action of igneous rocks. Formed probably by the action upon impure limestone of hot vapors containing water and fluorine given off by the igneous rock. Associated with other contact minerals, such as garnet, pyroxene, tourmaline, chondrodite, etc. Was originally discovered in the ancient ejections of Vesuvius and in the dolomitic blocks of Monte Somma. Important localities are, Zermatt, Switzerland; Ala, Piedmont; Monzoni, Trentino; Vesuvius; Christiansand, Norway; Achmatoosk, Urals; River Vilui, Siberia; from the states of Morelos and Chiapas, Mexico; in the United States, at Auburn and Sanford, Maine; near Amity, New York; from California including the com pact variety, californite; in Canada at Litchfield, Pontiac County; at Templeton, Quebec, etc.

Manual Of Mineralogy

Zircon Group

Zircon

Composition. ZrSiO., Silica 32.8, zirconia 67.2.

Crystallization. Tetragonal Crystals usually show a simple combination of prism and pyramid of the first order (Figs. 320 and 321). The prism of the second order and a ditetragonal pyramid also at times observed (Fig. 322). Base very rare. Crystal forms and axial ratio prove a close relationship between zircon and cassiterite and rutile.

Fig. 322.

Fig. 321.

Fig. 320.

Structure. Usually crystallized; also in irregular grains.

Physical Properties. H. 7.5. G. — 4.68. Luster adamantine. Usually nearly opaque, sometimes transparent. Color commonly some shade of brown; also colorless, gray, green, red. Streak uncolored. High refractive index.

Tests. Infusible. A small fragment when intensely ignited glows and gives off a white light. When fused with sodium car bonate and fusion then dissolved in dilute hydrochloric acid, the solution will turn a piece of turmeric paper to an orange color (zirconium). Recognized usually by its characteristic crystals, color, luster, hardness and high specific gravity.

Occurrence. Zircon is a common and widely distributed acces sory mineral in all classes of igneous rocks. It is especially frequent in the more acid types such as granite, syenite, diorite, etc. Very common in nephelite-syenite. It is the first one among the silicates to crystallize out from a cooling magma. Found also commonly in

Danburite

crystalline limestone, in gneiss, schist, etc. Found frequently as rounded pebbles in stream sands; often with gold. Gem zircons are found in the stream sands at Matura, Ceylon. Occurs in the gold gravels in the Urals, Australia, etc. In large crystals from Madagascar. Found in the nephelite-syenites of Norway and of Litchfield, Maine.' From Orange and St. Lawrence counties, New York. In considerable quantity in the sands of Henderson and Buncombe counties, North Carolina.

Use. When transparent serves as a gem stone. It is sometimes colorless, but more often of a brownish and red-orange color, called hyacinth or jacinth. The colorless, yellowish or smoky stones are called jargon, because while resembling the diamond they have little value; and thence the name zircon. Serves as the source of zirconium oxide, which with other rare oxides is used in the manu facture of the Welsbach incandescent mantle.

Thorite

Thorium silicate, ThSiO,j, always with some water, probably from alteration, and sometimes uranium. Tetragonal. Crystal forms resemble those of zircon. Also massive. Resinous to greasy luster. H- — 4.5-5. G. 4. 8-5. 2. Color orange-yellow, brown, black. Transparent to opaque. Infusible. Soluble in hydrochloric acid and gives gelatinous silica upon evaporation. A rare mineral, found chiefly in Norway, commonly altered. For uses of thorium see under monazite.

Danburite-Topaz Group

Danburite

Composition. Calcium-boron silicate,

Crystallization. Orthorhombic. Prismatic crystals, closely related to those of topaz in habit.

Structure. Commonly in crystals.

Physical Properties. H. 7-7.25. G. 2.97-3.02. Vitre ous luster. Colorless or pale yellow. Transparent to translucent.

Tests. Fusible (3.5-4), giving a green flame. Insoluble in acids.

Occurrence. Found in crystals at Danbury, Conn.; Russell, New York; eastern Switzerland; Madagascar; Japan.

Manual Of Mineralogy

Topaz

Composition. with isomorphous Crystallization. Orthorhombic. In prismatic crystals termi nated by pyramids, domes and basal plane (Figs. 323, 324 and 325). Often highly modified (Fig. 326). Prism faces often ver tically striated.

Fig. 324.

Structure. In crystalline masses; also granular, coarse or fine.

Physical Properties. Perfect basal cleavage. H. 8 (unusu ally high). G. 3.52-3.57. Vitreous luster. Colorless, yellow, yellow-brown, pink, bluish, greenish. Transparent to translucent.

Tests. Infusible. Insoluble. Recognized chiefly by its crys tals, its basal cleavage, its hardness (8) and high specific gravity.

Occurrence. A mineral formed through the agency of fluorine bearing vapors given off during the last stages of the solidification of igneous rocks. Found in cavities in rhyolite lavas and granite; a characteristic mineral in pegmatite veins, especially in those carry ing tin. Associated with other pneumatolytic minerals, as tour maline, cassiterite, apatite, fluorite, etc.; also with quartz, mica, feld spar. Found at times as rolled pebbles in stream sands. Notable localities for its occurrence are the Nerchinsk district in Siberia in large wine-yellow crystals; from Mursinsk, Ural Mts., in pale blue crystals; from various tin localities in Saxony; from Minas Geraes, Brazil; Omi and Mino Provinces, Japan; San Luis Potosi, Mexico; Pike's Peak, near Florissant and Nathrop, Colorado; Thomas Range, Utah; Streeter, Texas; San Diego Co., California; Stoneham, Maine.

Name. Derived from the name of an island in the Red Sea but originally probably applied to some other species.

Sillim An I Te

Use. As a gem stone. A number of other inferior stones are also frequently called topaz. The color of the stones varies, being colorless, wine-yellow, golden brown, pale blue and pink. The pink color is usually artificial, being produced by gently heating the dark yellow stones; it is permanent, however.

Andalusite. Chiastolite

Composition. Aluminum silicate, Al2Si05 Silica 36.8, alu mina 63.2.

Crystallization. Orthorhombic. Usually in coarse, nearly square prisms. Closely related crystallographically to topaz.

Structure. In crystals; massive.

Physical Properties. H. 7.5. G. 3.16-3.20. Vitreous luster. Flesh-red, reddish brown, olive-green.

Often with dark colored carbonaceous inclu sions forming a cruciform design, lying par allel to the axial directions (variety chiastolite or made) (see Fig. 327). Transparent to opaque. At times strongly dichroic, appear ing, in transmitted light, green in one direc tion and red in another.

Tests. Infusible. Insoluble. When fine powder is made into a paste with cobalt ni

Fig. 327.

Cross Section of Chi astolite Crystal.

trate and intensely ignited it turns blue (aluminum).

Occurrence. Found as a contact mineral in clayslates andschists, especially in connection with granite intrusions. Often impure and commonly, at least partly altered. Notable localities are in Anda lucia, Spain; the Tyrol; in water-worn pebbles from Minas Geraes, Brazil. In the United States at Standish, Maine; Westford, Lan caster and Sterling, Massachusetts; Delaware County, Pennsylvania. Chiastolite is found at Bimbowrie, South Australia; and Massa chusetts.

Use.

When clear and transparent may serve as a gem stone.

Sillimanite. Fibrolite

An aluminum silicate like andalusite, Al2Si05. An orthorhombic mineral, occurring in long slender crystals without distinct termina tions; often in parallel groups; frequently fibrous. Perfect pina-

Manual Of Mineralogy

coidal cleavage. H. 6-7. G. 3.23. Color hair-brown to pale green. Transparent to translucent. Infusible. Insoluble. A com paratively rare mineral, found as an accessory constituent of metamorphic rocks; gneiss, mica-schist, etc.

Cyanite

Composition. Aluminum silicate, like andalusite and sillimanite, Al2Si06.

Crystallization. Triclinic. Usually in long tabular crystals; terminations rare.

Structure. In bladed forms.

Physical Properties. Perfect pinacoidal cleavage. H. 5 parallel to length of crystals, 7 at right angles to this direction. G. 3.56-3.66. Vitreous to pearly luster. Color usually blue, often of darker shade toward the center of the crystal. Also at times white, gray or green.

Tests. Infusible. Insoluble. A fragment moistened with cobalt nitrate and ignited assumes a blue color (aluminum). Characterized by its bladed crystals, good cleavage, blue color and the fact that it is softer than a knife in the direction parallel to the length of the crystals but harder than a knife hi the direction at right angles to this.

Occurrence. An accessory mineral in gneiss and mica-schist, often associated with garnet, staurolite, corundum, etc. Notable localities for its occurrence are St. Gothard, Switzerland; in the Tyrol; Pontivy, Morbihan, France; Chesterfield, Massachusetts; Litchfield, Connecticut; Gaston and Yancey counties, North Carolina.

Name. Derived from a Greek word meaning blue.

Datolite

Composition. A basic orthosilicate of calcium and boron, Silica 37.6, boron trioxide 21.8, lime 35, water

Zoisite

Crystallization. Monoclinic. Habit varied. Crystals usu ally nearly equidimensional in the three axial directions and often complex in development (Fig. 328).

Structure. In crystals. Coarse to fine granular. Sometimes compact.

Physical Properties. H.

5-5.5. G. 2.8-3. Vitreous luster. Colorless, white, yellow.

Often with faint greenish tinge.

Transparent to translucent, rarely opaque.

Tests. Fuses at 2-2.5 to a clear glass and colors the flame green (boron). Soluble in hydrochloric acid and yields gelatinous silica on evaporation. Gives a little water in C. T. Characterized by its glassy luster, pale green color, and its crystals with many and usually irregularly developed faces.

Occurrence. A mineral of secondary origin, found usually in cavities in basalt lavas and similar rocks. Associated with various zeolites, with calcite, prehnite, etc. Occurs associated with the trap rocks of Massachusetts, Connecticut and New Jersey, particu larly at Westfield, Massachusetts, and Bergen Hill, New Jersey. Found associated with the copper deposits of Lake Superior. From Andreasberg, Harz Mts.; in Italy from near Bologna; from the Seiser Alpe and at Theiso, Trentino; Arendal, Norway; etc.

Name. Derived from a Greek word meaning to divide, allud ing to the granular structure of a massive variety.

A rare mineral belonging to the Datolite Group is gadolinite,

Fig. 328.

Epidote Group

Zoisite

Composition. HCazAhShOu Silica 39.7, alumina 33.7, lime 24.6, water 2.0.

Manual Of Mineralogy

Crystallization. Orthorhombic. Prismatic crystals usually without distinct terminations. Vertically striated.

Structure. In crystals; also massive.

Physical Properties. H. 6-6.5. G. 3.25-3.37. Vitre ous luster. Color grayish white, green, pink. Transparent to almost opaque.

Tests. Fuses at 3-4 with intumescence to a light colored slag. Yields a little water on intense ignition in C. T.

Occurrence. Usually in crystalline schists with one of the amphiboles. Thulite is a rose-pink variety.

Epidote

Composition. Iron occurs in varying amounts isomorphous with both the aluminum and cal cium.

Crystallization. Monoclinic. Crystals are often much elon gated parallel to the ortho-axis with a prominent development

of the faces of the orthodome zone, giving them a prismatic aspect. Stri ated parallel to the ortho-axis. Termi nated usually only at one end of the ortho-axis and most commonly by the two faces -of a pyramid (Fig. 329). Twinning shown at times.

a

r

Fig. 329.

Structure. Usually coarse to fine granular. In crystals. At times fibrous.

Physical Properties. Perfect basal cleavage. H. 6-7. G. 3.37-3.45. Vitreous luster. Color usually pistachio-green or yellowish to blackish green, sometimes gray. Transparent to opaque. Transparent varieties often show strong dichroism, appearing dark green in one direction, and brown in a direction at right angles to the first.

Tests. Fuses at 3-4 with intumescence to a black slag. On intense ignition in C. T. yields a little water.

Occurrence. Epidote occurs commonly in the crystalline metamorphic rocks; as gneiss, amphibolite and various schists. Is

Axinite

formed frequently also during the metamorphism of an impure limestone. Is the product of alteration of such minerals as feldspar, pyroxene, amphibole, biotite, scapolite, etc. Often associated with chlorite. Notable localities for its occurrence in fine crystals are Knappenwand, Unterzulzbachthal, Salzburg, Austria; Bourg d'Oisans, Isere, France; the Ala Valley and Traversella, Piedmont; Prince of Wales Island, Alaska; Haddam, Connecticut; Riverside, California.

Allanite

A mineral similar to epidote in composition, but containing con siderable amounts of the cerium metals, cerium, lanthanum and didymium, and sometimes with smaller amounts of yttrium and erbium. Composition complex and widely varying. Monoclinic, habit of crystals often similar to epidote. Commonly massive and in embedded grains. H. 5.5-6. G. 3.5-4.2. Submetallic to pitchy and resinous luster. Brown to pitch-black color. Fuses at 2.5 with intumescence. Sometimes magnetic after heating. Gelati nizes in acids. Occurs as a minor accessory constituent in many igneous rocks. Frequently associated with epidote.

Axinite

Composition. with varying amounts of fer rous iron, manganese, magnesium and hydrogen isomorphous with the calcium, and ferric iron with the aluminum.

Crystallization. Triclinic. Crystals usually thin with sharp edges but varied in habit (Fig. 330).

Structure. In crystals. Massive, lamellar to granular.

Physical Properties. Pinacoidal cleavage.

H. 6.5-7. G. 3.27-3.35. Vitreous luster.

Color clove-brown, gray, green, yellow.

Transparent to opaque.

Tests. Fusible at 2.5-3 with intumescence.

When mixed with potassium bisulphate and fluorite and the mixture heated on platinum wire gives a green flame (boron).

Occurrence. Occurs in cavities in graniteordiabase and especially in the contact zone of these rocks. Notable localities for its occur-

Fig. 330.

Manual Of Mineralogy

rence are Bourg d'Oisans, Isere, France; various points in Switzer land; St. Just, Cornwall; Obira, Japan; Franklin Furnace, New Jersey, etc.

Name. Derived from a Greek word meaning ax, in allusion to the wedgelike shape of the crystals.

Prehnite

Composition. fDCaAhShOn Silica 43.7, alumina 24.8, lime 27.1, water 4.4.

Crystallization. Orthorhombic. Distinct crystals rare.

Structure. Reniform, stalactitic. In rounded groups of tab ular crystals.

Physical Properties. H. 6-6.5. G. 2.8-2.95. Vitreous luster. Color usually light green, passing into white. Trans lucent.

Tests. Fuses at 2.5 with intumescence to an enamel. Heated in C. T. yields water. Slowly acted upon by hydrochloric acid but gelatinizes after simple fusion.

Occurrence. As a mineral of secondary origin lining amygdaloidal cavities in basalt, etc. Associated with zeolites, datolite, pectolite, calcite, etc. Occurs in the United States at Farmington, Connecti cut; Paterson and Bergen Hill, New Jersey; Somerville, Massa chusetts; Lake Superior copper district. Found also in various European localities.

4. Subsilicates Humite Group

The three minerals, humite, chrndrodite, and dinohumite, are closely related chemically and crystallographically. They are characteristically found in crystalline limestones. Chondrodite is the most common in occurrence.

Ilvaite, or lievrite, HCaFe*"Fe'"Si209, is a rare mineral belong ing in this section.

Calamine

Calamine

Composition. Silicate of zinc, Silica 25, zinc oxide 67.5, water 7.5.

Crystallization. Orthorhombic; hemimorphic. Crystals usu ally tabular parallel to the brachypinacoid. They show prism faces and are terminated above usually by a combination of macro domes and brachydomes and base, and below by a pyramid (Fig. 331).

Structure. Usually in crystal groups with the individuals attached at their lower (pyramidal) ends and lying with their brachypinacoid faces in common. Crystals often divergent, giving rounded groups with slight reentrant notches between the individual crystals, forming knuckle or coxcomb masses. Also mammillary, stalactitic, massive and granular.

Physical Properties. Prismatic cleavage.

H. 4.5-5. G. 3.4~3.5. Vitreous luster. Color white, some times with faint bluish or greenish shade; also yellow to brown. Transparent to translucent. Strongly pyroelectric

Tests. Fusible with difficulty at 5. Soluble in hydrochloric acid and yields gelatinous silica on evaporation. Fused on charcoal with sodium carbonate gives a nonvolatile coating of zinc oxide (yellow when hot, white when cold). Gives water in C. T. Rec ognized usually by the characteristic grouping of its crystals, but may be obscure and to be determined only by above tests.

Occurrence. A mineral of secondary origin, found in the oxidized portion of zinc deposits, associated with smithsonite, sphalerite, cerussite, anglesite, galena, etc. Usually with limestone rocks. Occurs at Moresnet, Belgium; Aix-la-Chapelle, Germany; in Carinthia; Rumania; Sardinia; Cumberland and Derbyshire, England; Algeria; Chihuahua, Mexico; Sterling Hill, near Ogdensburg, New Jersey; Friedensvilie, Pennsylvania; Wythe County, Virginia; with the zinc deposits of southwestern Missouri; Leadville, Colorado; Organ Mts., New Mexico; Elkhorn Mts., Montana.

Name. Supposed to be derived from cadmia, a name given by the ancients to the silicate and carbonate of zinc. The mineral

Fig. 331.

Manual Of Mineralogy

is called by English mineralogists hemimorphite or electric cala mine.

Use. An ore of zinc.

Tourmaline

Composition. A complex silicate of boron and aluminum, containing varying amounts of ferrous iron, magnesium, hangar nese, calcium, sodium, potassium, lithium, hydroxyl and fluorine.

Crystallization. Hexagonal-rhombohedral ; hemimorphic. Crystals usually prismatic, vertically striated. A triangular prism, with three faces, prominent, which with the tendency of the prism faces to be vertically striated and to round into each other gives the crystals usually a cross section like a spherical

Fig. 334.

triangle (Fig. 332). Crystals are commonly terminated by base and low positive and negative rhombohedrons; sometimes scalenohedrons are present. When the crystals are doubly terminated they usually show different forms at the opposite ends of the verti cal axis (hemimorphism) (Figs. 333 and 334).

Structure. Usually in crystals. Sometimes massive compact; also coarse to fine columnar, either radiating or parallel.

Physical Properties. Vitreous to resinous luster. Color varied, depending upon the composition. Common tourmahne with much iron is black, sometimes brown. More rarely colored in fine shades of red, pink, green, blue, yellow, etc. Rarely white or colorless. A single crystal may show several different colors either arranged in concentric bands about the center of the

Tourmaline

crystal or in transverse layers along its length. Strongly pyro electric; i.e., when cooling from being heated to about 100° C. it develops positive electricity at one end of the crystal and negative at the other, which enables the crystal to attract and hold bits of paper, etc. Strongly diehroic; i.e., light traversing the crystal in one direction may be of quite a different color or shade of color from that traversing the crystal in a direction at right angles to the first. H. 7-7.5; G. 2.98-3.2.

Tests. To be recognized usually by the characteristic rounded triangular cross section of the crystals; absence of prismatic cleavage, coal-like fracture of black variety.

Occurrence. Tourmaline is one of the most common and charac teristic minerals formed by pneumatolytic action. That is, it is a mineral that has been formed at high temperatures and pressures through the agency of vapors carrying boron, fluorine, etc. It is found, therefore, commonly as an accessory mineral in pegmatite veins, or dikes, occurring with granite intrusions. Associated with the ordinary minerals of granite pegmatite, orthoclase, albite, quartz and muscovite; also with lepidolite, beryl, apatite, fluorite, etc. Found also as an accessory inineral in metamorphic rocks, such as gneisses, schists and crystalline limestones.

The black tourmaline is of widespread occurrence as an accessory mineral in metamorphic rocks. The light colored gem varieties are found in the pegmatite dikes. Famous localities for the occur rence of the gem tourmalines are the island of Elba; in the state of Minas Geraes, Brazil; Ural Mountains near Ekaterinburg; Mada gascar; Paris and Auburn, Maine; Chesterfield, Massachusetts; Haddam Neck, Connecticut; Mesa Grande, Pala, Rincon and Ra mona in San Diego County, California. Brown crystals are found near Gouverneur, New York and fine black crystals at Pierrepont, New York.

Name. The name tourmaline comes from turamali, a name given to the early gems from Ceylon.

Use. Tourmaline forms one of the most beautiful of the semi precious gem stones. The color of the stones varies, the principal shades being olive-green, pink to red and blue. Sometimes a stone is so cut as to show different colors in different parts. The green-colored stones are usually known by the mineral name, tourmaline, or as Brazilian emeralds. The red or pink stones are

Manual Of Mineralogy

known as rubellite, while the rarer dark blue stones are called indicolite.

Staurolite

Composition. A ferrous iron-aluminum silicate, IIAUFe-

Si20l3.

Crystallization. Orthorhombic. Habit prismatic, showing usually a combination of prism with large angle (130°), brachypinacoid, base and macrodome (Fig. 335). Cruciform twins very common; of two types, (1) in which *the two individuals cross at nearly 90° (Fig. 336), (2) in which they cross at nearly 60° (Fig. 337). Sometimes both types are combined in one crystal.

Fig. 336.

Fig. 337.

Structure. Usually in crystals.

Physical Properties. H. 7-7.5. G. 3.65-3.75. Resin ous to vitreous luster, for pure and fresh material; often dull to earthy when altered or impure. Color red-brown to brownish black. Translucent to opaque.

Tests. Infusible. Insoluble. On intense ignition in C. T. yields a little water. Often very impure. Recognized by its characteristic crystals and twins.

Occurrence. Staurolite is an accessory mineral in metamorphic rocks; in crystalline schists, slates, and sometimes in gneisses. Often associated with garnet, cyanite, sillimanite, tourmaline. Not able localities for its occurrence are Monte Campione, Switzerland; in Brittany; Windham, Maine; Franconia and Lisbon, New Hamp shire; Chesterfield, Massachusetts; Fannin County, Georgia.

Apophyllite

Name. Derived from a Greek word meaning cross, in allusion to its cruciform twins.

Use. Occasionally a transparent stone from Brazil is cut as a

gem.

Hydrous Silicates

Zeolite Division Introductory Subdivision

Apophyllite

Composition. ILKCaSKDsAULO. Usually contains a small amount of fluorine.

Crystallization. Tetragonal. Usually shows a combination of prism of second order, pyramid of first and basal plane (Figs. 338 and 339). Small faces of a ditetragonal prism sometimes observed (Fig. 340) . Prism faces show vertical striations and have

a vitreous luster, while base shows pearly luster. Crystals may resemble an isometric combination of cube and octahedron, but are shown to be tetragonal by difference in luster between faces of prism and base.

Structure. In crystals; also massive and lamellar.

Physical Properties. Perfect basal cleavage. H. 4.5-5. G. 2. .>-3. 4. Luster of base pearly, other faces vitreous. Color usually colorless, white or grayish ; may show pale shades of green, yellow, rose. Usually transparent, rarely nearly opaque.

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Tests. Fuses easily with swelling to a white vesicular enamel. Colors the flame pale violet (potassium). Yields 16 per cent of water in C. T. Decomposed by hydrochloric acid with separation of silica but without the formation of a jelly. Solution gives little or no precipitate with ammonia but gives an abundant white precipitate with ammonium carbonate (calcium carbonate). Recognized usually by its crystals, color, luster and basal cleavage.

Occurrence. Occurs commonly as a secondary mineral lining cavities in basalt and related rocks. Associated with various zeo lites, with calcite, datolite, pectolite, etc. Found in fine crystals at Bergen HOI, Paterson, etc., New Jersey; Lake Superior copper dis trict; Nova Scotia; Guanjuato, Mexico; near Bombay, India; Andreasberg, Harz Mountains; Aussig, Bohemia; on the Seiser Alpe in Trentino, Italy; Faroe Islands; Iceland; Greenland, etc.

Name. Apophyllite, named from two Greek words meaning to get leaves, because of its tendency to exfoliate when ignited.

Zeolites

The zeolites form a large family of hydrous silicates which show close similarities in composition and in their associations and mode of occurrence. They are silicates of aluminum with sodium and calcium as the important bases. They average from 3.5 to 5.5. in hardness and from 2 to 2.4 in specific gravity. Many of them fuse readily with marked intumescence, hence the name zeolite, from two Greek words meaning to boil and stone. They are secondary minerals found characteristically in cavities and veins in basic igneous rocks.

Heulandite

Composition, Monoclinic, but crystals often simulate orthorhombic symmetry. Clinopinacoid prominent, having often a diamond shape. Perfect cleavage parallel to clino pinacoid. H. 3.5-4. G. 2.15-2.2. Vitreous luster, except on clinopinacoid, which is pearly. Color white, yellow, red. Trans parent to almost opaque. Fusible (3) with intumescence. Decom posed by hydrochloric acid with separation of silica. Water in C. T. A mineral of secondary origin found usually in cavities of basic igneous rocks associated with other zeolites, calcite, etc. Found in

Stilbite

notable quality in Iceland; the Faroe Islands; Andreasberg, Harz Mts. ; Tyrol, Austria; British India, near Bombay; West Paterson, etc., New Jersey; Nova Scotia.

Phillip site

Composition, Monoclinic. Crystals are uniformly penetration twins but often appearing to be tetragonal or orthorhombic in form. Cleavage parallel to base and clinopina coid. H. 4-4.5. G. 2.2. Vitreous luster. White or reddish in color. Translucent to opaque. Fuses at 3 to a white enamel. Gelatinizes with hydrochloric acid. Water in C. T. A secondary mineral found in cavities of igneous rocks associated with other zeolites, etc.

Harmotone

A barium zeolite having the composition Monoclinic. Crystals are uniformly cruciform penetration twins. Perfect cleavage parallel to clinopinacoid. H. 4.5. G. 2.4- 2.5. Vitreous luster. Colorless or white. Translucent. Fuses at 3. Decomposed by hydrochloric acid with separation of silica. Addition of sulphuric acid to hydrochloric acid solution gives a white precipitate of barium sulphate. Water in C. T.

A mineral of secondary origin, occurring in cavities of basic igneous rocks, associated with other zeolites, calcite, etc.

Stilbite. Desmine

C omp osition. (Na2, Ca) Al2Si60i 6. 6H20 .

Crystallization. Monoclinic. Uniformly in cruci form twins. Commonly tabular parallel to clino pinacoid. Crystals usually in sheaflike aggregates (Fig. 341).

Structure. In crystal groups, divergent or radi ated. #

Physical Properties. Perfect cleavage parallel to clinopina coid. H. 3.5-4. G. 2. 1-2.2. Vitreous luster; pearly on clinopinacoid. Color white, yellow, brown, red. Translucent.

Tests. Fuses with intumescence at 3. Decomposed by hydro chloric acid with separation of silica but without the formation

manual of mineralogy

of a jelly. Water in C. T. Characterized chiefly by its cleavage, pearly luster on the cleavage face and common sheaflike groups of crystals.

Occurrence A mineral of secondary origin found in amygdaloidal

zSS m |3afsa tsf and related rocks. Found associated with other

n.,l! r' hCa CJtT' et,Co, Notable localities for its occurrence are Poo-

Hnd-nw-n Is e °fMkyer; Far5e Islands>' Kilpatrick, Scotland; Ice land, northeastern New Jersey; Nova Scotia.

Name. Derived from a Greek word meaning luster.

Laumontite

A zeolite with composition H4CaAl2Si40I4.2H20. Monoclinic. In prismatic crystals with oblique terminations; columnar. Cleav age parallel to prism and clinopinaeoid. H. 3.5— J. G. 2 25- 2.35. Vitreous to pearly luster. Color white or gray. Alters on exposure, becoming opaque and pulverulent. Fusible (2.5) Gelat inizes m acids. Water in C. T. Found as a mineral of secondary

origin in cavities of basic igneous rocks, associated with other zeoiites, etc.

Chabazite

Composition. Usually corresponds to but different analyses show considerable variation from this for mula, so that the composition is still uncertain.

Crystallization. Hexagonalrhombohedral. Common form is the simple rhombohedron r, having nearly cubic angles. May show several different rhombohedrons (Fig. 342). Often in penetration twins.

Fig. 342. Structure. Usually in crystals.

Physical Properties. H.

4-5. G. 2.05-2.15. Vitreous luster. Color white, yellow, flesh-red. Transparent to translucent.

Tests. Fuses with swelling at 3. Decomposed by hydro chloric acid with the separation of silica but without the formation

Analcite

of a jelly. Solution after filtering off silica gives precipitate of aluminum hydroxide with ammonia, and in filtrate ammonium carbonate gives white precipitate of calcium carbonate. Gives much water in C. T. Recognized usually by its crystals.

Occurrence. A mineral of secondary origin found usually with other zeolites, lining amygdaloidal cavities in basalt. Notable localities for its occurrence are the Faroe Islands; the Giant's Cause- " ay, Ireland; at Aussig, Bohemia; Seiser Alpe, Trentino, Italy; Oberstein, Germany; West Paterson, etc., New Jersey; Goble Station, Oregon; in Nova Scotia, etc.

Name. Chabazite is derived from a Greek word which was an ancient name for a stone.

Gmelinite, (Na2,Ca) AhShO.fil'hO, is closely related to chabazite but rarer in occurrence.

Analcite

Composition. Hydrous sodium-aluminum metasilicate, Na- AlSi206.H20 Silica 54.5, alumina 23.2, soda 14.1, water 8.2. Note similarity in composition to leucite, KAlSi206.

Fig. 343.

Fig. 344.

Crystallization. Isometric. Usually in trapezohedrons (Fig.

343) . Cubes with trapezohedral truncations also known (Fig.

344) .

Structure. Usually in crystals, also massive granular. Physical Properties. H. 5-5.5. G. 2.27. Vitreous lus ter. Colorless or white. Transparent to nearly opaque.

Manual Of Mineralogy

Tests. Fusible at 3.5, becoming first opaque and then a clear glass. Colors the flame yellow (sodium). Decomposed by hy drochloric acid with the separation of silica without the formation of a jelly. Gives water in C. T. Usually recognized by its crystals and its vitreous luster.

Occurrence. Commonly a secondary mineral, formed by the action of hot circulating waters, and is to be found deposited in the cavities of igneous and especially volcanic rocks. Associated with calcite, and various zeolites and related minerals. Also at times as an original constituent of igneous rocks, as in the analcite-basalts. Fine crystals found at Bergen Hill, etc., New Jersey; in the Lake Superior copper district; at Table Mountain, near Golden, Colorado; at Cape Blomidon, etc., Nova Scotia; in the Cyclopean Islands near Sicily; in the Val di Fassa and on the Seiser Alpe, Trentino, Italy; from Victoria, Australia; Kerguelen Island in the Indian Ocean.

Name. Derived from a Greek word meaning weak, in allusion to its weak electric power when heated or rubbed.

Natrolite

Composition. Na2Al2Si3Oi0.2H2O. A zeolite.

Crystallization. Orthorhombic. Crystals usually slender prismatic, often acicular. Prism zone vertically striated. Some times terminated by low pyramid. Crystals often appear to be tetragonal in symmetry. Sometimes in cruciform twins.

Structure. Usually in radiating crystal groups (see Fig. C, pi. II) ; also fibrous, massive, granular or compact.

Physical Properties. Perfect prismatic cleavage. H. 5-5.5. G. 2.25. Vitreous luster. Colorless or white. Sometimes tinted yellow to red. Transparent to translucent.

Tests. Easily fusible (2.5) to a clear, transparent glass giving a yellow (sodium) flame. Water in C. T. Soluble in hydrochloric acid and gelatinizes upon evaporation. Recognized chiefly by its radiating crystals.

Occurrence. A mineral of secondary origin, found lining amvgdaloidal cavities in basalt, etc. Associated with other zeolites, calcite, etc. Notable localities for its occurrence are Aussig and Salesel Bohemia; Puy-de-Dome, France; Val di Fassa, Trentino, Italy; in various places in Nova Scotia; Bergen Hill, etc., New Jersey.

Mica Group

Scolecite

A zeolite with composition CaAI2Si3Oio.3H20. Monoclinic. In slender prismatic, twinned crystals. In radiating groups. Some times fibrous. Prismatic cleavage. H. 5-5.5. G. 2.16-2.4. Vitreous luster; silky when fibrous. Colorless or white. Trans parent to almost opaque. Fuses at 2.5 to a voluminous frothy slag. Gelatinizes in acids. Water in C. T. A mineral of secondary origin, found lining cavities in basic igneous rocks, associated with other zeolites, etc.

Thomsonite

A zeolite, having the composition Orthorhombic but distinct crystals rare. Commonly columnar with radiated structure. Perfect pinacoidal cleavage. H. 5-5.5. G. 2. 3-2. 4. Vitreous luster. Colorless, white, gray. Trans parent to translucent. Fuses with intumescence at 2-2.5. Soluble and gelatinizes in acids. Much water in C. T. Occurs in amygdaloidal cavities in basalt, etc., associated with other zeolites.

Mica Division Mica Group

The micas form a series of complex silicates of aluminum with potassium and hydrogen, also often magnesium, ferrous iron, and in some varieties, sodium, lithium, ferric iron. More rarely manganese, chromium, barium, fluorine and titanium are present in small amounts. The composition of many of the micas is not definitely understood and the formulas assigned to them are only approximate.

They crystallize in the monoclinic system but with an axial inclination of practically 90°, so that their monoclinic symmetry is not clearly seen. The crystals are usually tabular with promi nent basal planes, and have either a diamond- or hexagonal-shaped outline with angles of 60° and 120°. The crystals, as a rule, there fore, appear to be either orthorhombic or hexagonal in their sym metry. They are all characterized by a veiy perfect basal cleavage.

They form an isomorphous series, and various gradations between the different members occur. Their isomorphism is

Manual Of Mineralogy

further indicated by two members of the group frequently crys tallizing together, with a parallel position, in the same crystal plate. Biotite occurs crystallizing in this way with muscovite, and muscovite with lepidolite, etc.

The important members of the group follow:

Muscovite,

Lepidolite, KLi[ A1 . 2 (OH,F) ] A1 (Si03) 3.

Biotite,

Phlogopite,

Lepidomelane,

Muscovite. Common Mica

Composition. Contains also frequently small amounts of ferrous and ferric iron, magnesium, calcium, sodium, lithium, fluorine, titanium, etc.

Crystallization. Monodinic with axial angle nearly 90°. Occurs in tabular crystals with prominent base. The presence of prism faces having angles of 60° and 120° with each other gives the plates a diamond-shaped outline, making them simulate ortho rhombic symmetry. If the clinopinacoid faces are also present, the crystals become hexagonal in outline with apparently hexagonal symmetry. The prism faces are roughened by horizontal striations and frequently taper.

Structure. Foliated in large to small sheets; in scales which are sometimes aggregated into plumose or globular forms. Dis tinct crystals comparatively rare.

Physical Properties. Extremely perfect cleavage parallel to base, allowing the mineral to be split into excessively thin sheets. Folia flexible and elastic. H. 2-2.5. G. 2.76-3. Vitre ous to silky or pearly luster. Transparent and almost colorless in thin sheets. In thicker blocks, opaque with light shades of brown and green. May be yellow to white. Some crystals are translu cent when viewed perpendicular to the prism zone but opaque in a direction perpendicular to the base.

Tests. Fusible at 4.5-5. Unattacked by boiling hydrochloric or sulphuric acids. Characterized by its micaceous structure and

Muscovite

light color. Told from phlogopite by its not being decomposed in sulphuric acid and from lepidolite by not giving a crimson flame

B. B.

Occurrence. A widespread and very common rock-making min eral. Found in such igneous rocks as granite and syenite. Espe cially characteristic of pegmatite veins, and found lining cavities in granites, where it has evidently been formed by the action of mineralizing vapors during the last stages of the formation of the rock. Muscovite is chiefly characteristic of the deep-seated igneous rocks, and is found rarely in the recent eruptive rocks. Also very common in metamorphic rocks, as gneiss and schist, forming the chief constituent in certain mica-schists. In some schistose rocks it occurs in the form of fibrous aggregates of minute scales having a silky luster, but which do not show so plainly the characters of the mineral. This variety is known as sericite, and is usually the prod uct of alteration of feldspar. Muscovite also originates, as the alteration product of several other minerals, as topaz, cyanite, spodumene, adalusite, scapolite, etc. Pinite is a name given to the micaceous alteration product of various minerals, and which corre sponds in composition more or less closely to muscovite.

In the pegmatite veins, muscovite occurs associated with quartz and feldspar, with tourmaline, beryl, garnet, apatite, fluorite, etc. It is found often in these veins in large blocks, which are at times several feet across.

Muscovite is found in the United States in commercial deposits chiefly in the Appalachian and Rocky Mountain regions. The most productive pegmatite veins occur in New Hampshire and in North Carolina, and in the Black Hills of South Dakota. Of less importance are the deposits in Colorado, Alabama and Virginia. Muscovite has been mined in Maine and Connecticut. Large de posits are found in Canada in the township of Grenville, east of Ottawa, and in a district to the east of Quebec. Large and important deposits occur in India.

Name. Muscovite was so called from the popular name of the mineral, Muscovy-glass, because of its use as a substitute for glass in Russia. Mica was probably derived from the Latin micare, meaning to shine.

Use. Used chiefly as an insulating material in the manufacture of electrical apparatus. Used as a transparent material (isinglass) for stove doors, lanterns, etc. Scrap mica, or the waste material in the manufacture of sheet mica, is used in many ways, as in the manufacture of wall papers to give them a shiny luster; as a lubri-

Manual Of Mineralogy

cant when mixed with oils; as a nonconductor of heat and as a fireproofing material.

Lepidolite

Composition. Lithia mica,

Crystallization. Monoclinic. Crystals usually in small plates or prisms with hexagonal outline.

Structure. Commonly in coarse- to fine-grained scaly aggre gates.

Physical Properties. Perfect basal cleavage. H. 2.5-4. G. 2.8. Pearly luster. Color pink and lilac to grayish white. Translucent.

Tests. Easily fusible (2), giving a crimson flame (lithium). Insoluble in acids. Characterized chiefly by its micaceous struc ture and lilac to pink color.

Occurrence. A comparatively rare mineral, found in pegmatite veins, usually associated with pink and green tourmaline, cassiterite, amblygonite, spodumene, etc. Often intergrown with muscovite in parallel position. Notable localities for its occurrence are at Rozna, Moravia; Madagascar; western Maine at Hebron, Auburn, Norway, Paris, Rumford; near Middletown, Connecticut; San Diego County, California.

Name. Derived from a Greek word meaning scale.

Use. A source of lithium compounds.

Biotite

Composition.

Crystallization. Monoclinic. In tabular or short prismatic crystals with prominent basal planes. Crystals rare, frequently pseudorhombohedral.

Structure. Usually in irregular foliated masses; often in dis seminated scales or in scaly aggregates.

Physical Properties. Perfect basal cleavage. Folia flexible and elastic. H. 2.5-3. G. 2.95-3. Splendent luster. Color usually dark green and brown to black. More rarely lighter

Ph Logo Pi Te 291

yellow. Thin sheets usually have a smoky color (differing from the almost colorless muscovite).

Tests. Difficultly fusible at 5. Unattacked by hydrochloric acid. Decomposed by boiling concentrated sulphuric acid, giving a milky solution. Characterized by its micaceous structure, cleavage and dark color.

Occurrence. An important and widely distributed rock-making mineral, but not as common as muscovite. Occurs in igneous rocks, especially those in which feldspar is prominent, such as granite and syenite. At times in pegmatite veins in large sheets. Found also in many felsite lavas and porphyries. Less common in the ferromagnesium rocks. Is also present in some metamorphosed rocks, as gneiss and schist. Occurs in fine crystals in the lavas of Vesuvius.

Phlogopite

Composition. A.magnesium mica, near biotite, but containing no iron, ILKMgjASiChM?). Usually contains about 3 per cent of fluorine.

Crystallization. Monoclinic. Usually in six-sided plates or in tapering prismatic crystals. Crystals frequently large and coarse.

Structure. In crystals or foliated masses.

Physical Properties. Perfect basal cleavage. Folia flexible and elastic. H. 2.5-3. G. 2.86. Luster vitreous to pearly. Color yellowish brown, green, white, often with copper-like re flections from the cleavage surface. Transparent in thin sheets to opaque in the mass.

Tests. Fusible at 4.5-5. Insoluble in hydrochloric acid. Decomposed by boiling concentrated sulphuric acid, giving a milky solution. Characterized by its micaceous structure, cleav age and yellowish brown color. Told from muscovite by its de composition in sulphuric acid and from biotite by its lighter color. But it is impossible to draw a sharp distinction between biotite and phlogopite.

Occurrence. Occurs as a product of metamorphism in crystalline magnesium limestones or dolomitic marbles and is also found in serpentine. Rarely found in igneous rocks. Notable localities are

Manual Of Mineralogy

in Finland; Sweden; Campolungo, Switzerland; Ceylon; Madagascar, etc. In North America, found chiefly in Jefferson and St. Lawrence counties, New York; at North and South Burgess, Ontario, and in various localities in Ontario and Quebec, Canada.

Name. Named from a Greek word meaning firelike, in allusion to its color.

Use. Same as for muscovite.

Lepidomelane

A mica, that may be regarded as a variety of biotite, characterized by the large amount of ferric iron that it contains, Monoclinic. In small hexagonal-shaped tables, or as an aggregate of minute scales. Perfect basal cleavage. H. 3. G. 3-3.2. Adamantine to pearly luster. Color black to greenish black. Opaque or translucent in very thin laminae. Fuses at 4.5-5 to a magnetic globule. Decomposed, by hydrochloric acid. A comparatively rare mineral, found chiefly in pegmatitic granites and syenites.

Clintonite Group

The minerals of this group are rare species that lie between the true micas and the chlorites. They resemble the micas in crystal forms, cleavage, etc., but differ physically in that their folia are brittle, and chemically in that they are basic in character. The only species in the group that warrants description is margarite.

Margarite

A micaceous mineral with the composition HsCaAbSLOu. Mono clinic but seldom in distinct crystals. Usually in foliated aggregates. Perfect basal cleavage. H. 3. 5-4. 5 (harder than the true micas). G. 3.05. Luster vitreous to pearly. Color pink, white and gray. Translucent. Folia somewhat brittle. Fuses at 4-4.5. Unat tacked by acids. Occurs usually with corundum and apparently as one of its alteration products. Found in this way with the emery deposits of Asia Minor; on the islands of the Greek archipelago; at Chester, Massachusetts; Chester County, Pennsylvania; with co rundum deposits in North Carolina, etc.

Clinochlore

Chlorite Group

A somewhat ill-defined group of closely related micaceous min erals is known as the Chlorite Group or as the chlorites. They are so named on account of the characteristic green color that they show. They are silicates of aluminum with magnesium, ferrous iron and hydroxyl. Ferric iron may replace the aluminum in small amount. Chromium and manganese may occur. Calcium and the alkalies, which are characteristic of the micas proper, are practically absent. The composition of these minerals is not fully understood. Their crystal forms are similar to those of the micas and they show a perfect basal cleavage. Their laminae, however, are tough and inelastic. Clinochlore is the most common member of the group.

Clinochlore. Penninite

Composition. H8Mg5Al2Si30i8. See above.

Crystallization. Monoclinic. In six-sided tabular crystals, with prominent basal planes. Similar in habit to the crystals of the mica group, but distinct crystals rare. Penninite is pseudorhombohedral in symmetry, otherwise it is identical with clino chlore.

Structure. Usually foliated massive or in aggregates of minute scales; in finely disseminated particles; earthy.

Physical Properties. Perfect basal cleavage. Folia flexible but not elastic. H. 2-2.5. G. 2.65-2.75. Vitreous to pearly luster. Color green of various shades. Rarely pale green, yellow, white, rose-red. Transparent to opaque.

Tests. Difficultly fusible, 5-5.5. Unattacked by hydrochloric acid. Decomposed by boiling concentrated sulphuric acid, giving a milky solution. Characterized by its green color, micaceous structure and cleavage and by the fact that the folia are not elastic.

Occurrence. A common and widespread mineral, usually of sec ondary origin and occurs in connection with chloritic and talcose rocks or schists and serpentines. It results from the alteration of silicates containing aluminum, ferrous iron and magnesium, such as pyroxene, amphibole, biotite, garnet, vesuvianite, etc. 1 o be found

Manual Of Mineralogy

where rocks, containing such minerals, are undergoing metamorphic change. The green color of many igneous rocks is due to the chlorite into which the ferromagnesian silicates have altered. The green color of many schists and slates is due to finely disseminated particles of the mineral.

Name. Chlorite is derived from a Greek word meaning green, in allusion to the common color of the mineral.

Serpentine

Composition. A magnesium silicate, ILMgjSLO# Silica 44.1, magnesia 43.0, water 12.9. Ferrous iron and nickel may be present in small amount.

Crystallization. Monoclinic (optically). Occurs, however, only in pseudomorphic crystals.

Structure. Often in delicate fibers, which can be separated from each other (see Fig. D, pi. II). Usually massive, but micro scopically fibrous and felted.

Physical Properties. H. 2.5-5, usually 4. G. 2.5-2.65. Luster greasy, waxlike in the massive varieties, silky when fibrous. Color olive to blackish green, yellowish green, white. Color often variegated, showing mottling in lighter and darker shades of green. Translucent to opaque.

Tests. Infusible. Decomposed by hydrochloric acid with the separation of silica but without the formation of a jelly. Filtered solution, after being oxidized with nitric acid and having any iron precipitated by ammonium hydroxide, and the absence of calcium proved by addition of ammonium oxalate, gives a precipitate of ammonium-magnesium phosphate with sodium phosphate. Water in C. T. Recognized by its variegated green color and its greasy luster or by its fibrous structure.

Varieties. In Crystals. Occurs in crystals as pseudomorphs after various magnesian silicates, principally chrysolite, pyroxene, amphibole.

Precious Serpentine. Massive, translucent, of light to dark green color. Often mixed with white marble and shows beautiful variegated coloring. Frequently called verd antique marble.

Genthite

Ordinary Serpentine. Massive, opaque, of various shades of green.

Chrysotile. The fibrous asbestiform variety, which is to be found in veins traversing the massive serpentine. This is the asbestos of commerce for the most part.

Occurrence. A common mineral and widely distributed. Always as an alteration product of some magnesian silicate, especially chryso lite, also pyroxene, amphibole, etc. Frequently associated with magnesite, chrysolite, chromite, etc. Found in both igneous and metamorphic rocks, sometimes in disseminated particles, sometimes in such quantity as to make up practically the entire rock-mass. Precious serpentine is found at many localities. The fibrous variety, chrysotile, comes from the Province of Quebec, Canada, just north of the Vermont line; from Vermont; New York; New Jersey; in Arizona near Globe, from the Sierra Ancha and in the Grand Canyon.

Name.. The name refers to the green serpentlike cloudings of the massive variety.

Use. The variety chrysotile is the chief source of asbestos. Fibrous amphibole (which see) is also used for the same purposes. The uses of asbestos depend upon its fibrous, flexible structure, which allows it to be woven into cloth, felt, etc., and upon its incombustibility and slow conductivity of heat. Asbestos prod ucts, therefore, are used for fireproofing and as an insulating material against heat and electricity. The massive mineral is often used as an ornamental stone and may at times be valuable as building material.

Genthite. Gamierite

Nickel silicates of uncertain composition. Genthite contains mag nesium, NhMgjSijOio.filFOi?) ; Gamierite , H2NiSi04(?). Amorph ous, earthy to slightly botryoidal structure. As incrustations. H. 3— t. G. 2.2-2.8. Earthy and dull luster. Color apple-green to white. Infusible. Difficultly decomposed by hydrochloric acid, giving separated silica. In O. F. color the borax bead brown. In C. T. blacken and give water. Genthite found with chromite at Texas, Lancaster County, Pennsylvania. Gamierite occurs in con siderable amount, associated with serpentine and chromite, near Noumea, New Caledonia, and serves as an important ore of nickel.

Manual Of Mineralogy

Talc. Steatite. Soapstone

Composition. A magnesium silicate, Silica 63.5, magnesia 31.7, water 4.8.

Crystallization. Monoclinic. Crystals rare. Usually tabu lar with rhombic or hexagonal outline.

Structure. Foliated massive; sometimes in radiating foliated groups. Also compact.

Physical Properties. Perfect basal cleavage. Thin folia somewhat flexible but not elastic. Sectile. H. 1 (will make a mark on cloth). G. 2.8. Pearly to greasy luster. Color apple-green, gray, white; in soapstone often dark gray or green. Translucent to opaque. Greasy feel.

Tests. Difficultly fusible (5). Unattacked by acids. Char acterized by its micaceous structure and cleavage, by its softness and greasy feel. To be distinguished from pyrophyllite by mois tening a fragment with cobalt nitrate and heating intensely; talc will assume a pale violet color, pyrophyllite a blue color.

Varieties. Foliated Talc. Light green or white, foliated, with a greasy feel.

Steatite or Soapstone. Massive, with fine granular to crypto crystalline structure. Gray to dark green colors; often impure, through the presence of such minerals as chlorite, tremolite, mica, etc.

Pseudomorphous. Is frequently pseudomorphous after such minerals as enstatite, pyroxene, amphibole, chrysolite, etc.

Occurrence. Talc is a mineral of secondary origin formed by the alteration of magnesium silicates, such as chrysolite, enstatite, pyroxene, amphibole, etc. Found at times in the igneous rocks, because of the alteration of such silicates, especially in peridotites and pyroxenites. Most characteristically found, however, in the metamorphic rocks, where it may form as soapstone, practically the entire rock-mass, or occur as a prominent constituent in the schistose rocks, as in talc-schist. In the United States, talc or soapstone quarries are to be found chiefly along the line of the Appalachian Mountains, the mineral being produced in Vermont, Massachusetts, Rhode Island, New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, and Georgia. Important deposits are located in St. Lawrence County, New York, where the talc occurs

Kaolin Or Kaolinite

in the form of beds of schist interstratified with limestones. It is associated here with tremolite and enstatite, from masses of which it has evidently been derived. Large deposits of soapstone occur in Virginia in a narrow belt running from Nelson County northeast into Albemarle County. It occurs here in sheets sometimes 100 or more feet in thickness. There is a long series of talc and soapstone deposits in Vermont, located along the east side of the Green Moun tains. Talc has been mined in considerable quantity in Swain County, North Carolina; also from California.

Use. In the form of slabs, soapstone is used extensively for wash tubs, sinks, table tops, electrical switchboards, hearthstones* furnace linings, etc. An especially compact variety is used for the tips of gas burners, for tailors' chalk, slate pencils, by the Chinese for carvings, etc. Talc is also used in.a finely powdered form as a filler to give weight to paper, as a lubricant, for toilet powders, in paints, as a heat insulator, etc.

Kaolin or Kaolinite

Composition. An aluminum silicate, KAXSLOo Silica 46.5, alumina 39.5, water 14.

Crystallization. Monoclinic. In very minute, thin, rhombic or hexagonal-shaped plates.

Structure. Usually in claylike masses, either compact or friable.

Physical Properties. Perfect basal cleavage. H. 2-2.5. G. 2.6-2.63. Luster usually dull earthy; crystal plates pearly. Color white. Often variously colored by impurities. Usually unctuous and plastic.

Tests. Infusible. Insoluble. Assumes a blue color when moistened with cobalt nitrate and ignited (aluminum). Recog nized usually by its claylike character.

Occurrence. Of widespread occurrence. The chief constituent of clay. Always a mineral of secondary origin, being derived by the alteration of aluminum silicates, particularly feldspar. It is found mixed with feldspar in rocks that are undergoing alteration; at times it forms entire beds where such alteration has been carried to completion. As one of the common products of the decomposition of rocks it gets into soils and being transported by water is deposited,

Manual Of Mineralogy

mixed with quartz and other materials in lakes, etc., in the form of beds of clay.

Name. Kaolin is a corruption of the Chinese, Raiding, a locality from which material was obtained for the manufacture of porcelain and which was thought to be the same as kaolin.

Use. Used in the form of clay in making all kinds of pottery, stoneware, bricks, etc. The finer, purer grades of kaolin are used in the manufacture of porcelain, china, etc.

Pyrophyllite

Composition. Silica 66.7, alumina 28.3, water

Crystallization. Monoclinic (?). Not observed in crystals.

Structure. Foliated, sometimes in radiating lamellar aggre gates. Also granular to compact. Identical with talc in struc ture and appearance.

Physical Properties. Perfect basal cleavage. Folia some what flexible but not elastic. H. 1-2 (will make a mark on cloth). G. 2.8-2.9. Pearly to greasy luster. Color white, apple-green, gray, brown. Usually opaque. Greasy feel.

Tests. Infusible. Unattacked by acids. Characterized chiefly by its micaceous structure and cleavage, its softness and greasy feel. Only to be easily distinguished from talc by moistening a small fragment with cobalt nitrate and igniting, when it assumes a blue color (aluminum). Talc under the same conditions would become pale violet.

Occurrence. A comparatively rare species. Found in metamorphie rocks; frequently with cyanite. Occurs in considerable amount in Guilford and Orange counties, North Carolina.

Use. Quarried in North Carolina and used for the same pur poses as talc. It does not command, however, as high a price as the best grades of talc. A considerable part of the so-called agalmatolite, from which the Chinese carve small images, is this species.

Titanite

Chrysocolla

Composition. Hydrous copper silicate, whose formula is near CuSi03. 211,(3. Varies considerably in composition and often impure, and is commonly considered to be usually a solid solution of CuO, Si02 and H20 in varying proportions.

Structure. Has been observed in small, acicular crystals but commonly cryptocrystalline or amorphous. Massive compact. Sometimes earthy.

Physical Properties. H. 2-4. G. 2.0-2.4. Luster vit reous to earthy. Color green to greenish blue; brown to black when impure.

Tests. Infusible. Decomposed by hydrochloric acid with the separation of silica but without the formation of a jelly. Gives a copper globule when fused with sodium carbonate on charcoal. In C. T. darkens and gives water.

Occurrence. A mineral of secondary origin, occurring in the oxidized zones of copper veins. Associated with malachite, azurite, cuprite, native copper, etc. Found in the copper districts of Arizona and New Mexico. In microscopic crystals from Mackay, Idaho.

Name. Chrysocolla, derived from two Greek words meaning gold and glue, which was the name of a similar appearing material used to solder gold.

Use. A minor ore of copper.

Titanite. Sphene

Composition. Calcium titano-silicate, CaTiSi05 Silica 30.6, titanium oxide 40.8, lime 28.6. Iron is usually present in small amounts.

Crystallization. Monoclinic. Crystals varied in habit. Often with prominent basal plane which is steeply inclined and which in combination with short prism and pyramid faces gives a thin wedge-shaped crystal (Figs. 345 and 346).

Structure. Usually crystallized or lamellar.

Physical Properties. Prismatic cleavage. H. 5-5.5. G. 3.4-3.55. Resinous to adamantine luster. Color gray, brown, green, yellow, black. Transparent to opaque.

Manual Of Mineralogy

Tests. Fusible at 4 with slight intumescence to a dark mass. Only slightly attacked by hydrochloric acid. Fused with sodium carbonate; fusion dissolved in hydrochloric acid; the solution when boiled with tin gives a violet color (titanium).

Occurrence. A rather common accessory mineral in igneous rocks, being found as small crystals in granites, diorites, syenites, nephelitesyenites, etc. Also found often in crystals of considerable size em bedded in the metamorphic rocks, gneiss, chlorite-schist and crys talline limestone. Very commonly associated with chlorite. Also found with iron ores, pyroxene, amphibole, scapolite, zircon, apatite, feldspar, quartz, etc. Notable localities for its occurrence in crystals are Tavetsch, Binnental, St. Gothard, etc., Switzerland; Ziliertal, Tyrol; Ala, Piedmont; Vesuvius; Arendal, Norway; Diana, Rossie, Fine, Pitcairn, Edenville, Brewster, etc., in New York; in various places in Ontario and Quebec, Canada.

Name. Sphene comes from a Greek word meaning wedge in allusion to a characteristic development of the crystals.

Perovskite, CaTi03, is a rare isometric titanate.

NIOBATES — TANTALATES Columbite — Tantalite

Composition. A niobate and tantalate of ferrous iron and manganese (Fe,Mn) which varies in composition from the niobate, columbite to the tantalate, tantalite Often contains small amounts of tin, tungsten, etc. A variety, known as manganotantalite, is essentially a tantalite with most of the iron replaced by manganese.

Columbite — Tantalite

At times in

Crystallization. Orthorhombic. Habit of crystals is short prismatic; often in square prisms because of prominent develop ment of the vertical pinacoids. Terminated by basal plane, pyramids and domes; frequently complex (Fig. 347) heart-shaped contact twins.

Structure. Crystallized and in par allel crystal groups. Also frequently granular massive.

Physical Properties. H. 6.

G. 5.3-7.3, varying with the com position, increasing with rise in per centage of tantalum oxide present.

Submetallic luster. Color iron-black, frequently iridescent. Streak dark red to black.

Tests. Difficultly fusible (5-5.5). Fused with borax; the bead dissolved in hydrochloric acid; the solution boiled with tin gives a blue color (niobium) . There is no simple test for tantalum. Generally when fused in O. F. with sodium carbonate gives an opaque bluish green bead. Fused with sodium carbonate on char coal in R. F. yields a magnetic mass. Recognized usually by its black color, submetallic streak and high specific gravity.

Occurrence. Occurs in granite rocks and in pegmatite veins, associated with quartz, feldspar, mica, tourmaline, beryl, spodumene, cassiterite, samarskite, wolframite, microlite, monazite, etc. Notable localities for its occurrence are the west coast of Greenland; near Moss, Norway; Bodenmais, Bavaria; Ilmen Mountains, Russia; Western Australia (manganotantalite); Madagascar; Standish, Maine; Haddam, Middletown and Branchville, Connecticut; in Amelia County, Virginia; Mitchell County, North Carolina; Black Hills, South Dakota; near Canon City, Colorado.

Name. The two names are derived from the acid elements that the minerals contain. Niobium is often called columbium.

Use. Source of tantalum, which has been used in making fila ments for incandescent electric lamps. Tantalum is also a constit uent of various iron alloys.

Manual Of Mineralogy

There are a number of other niobates and tantalates, all of which are rare in occurrence. The following, however, might be men tioned : pyrochlore, chiefly a niobate of the cerium metals and cal cium; microlite, essentially Ca2Ta207; fergusonite, a niobate of yttrium, erbium, cerium, uranium, etc.; samarskite, a niobate and tantalate of ferrous iron, uranium and the cerium metals.

Phosphates, Etc.

The phosphates and the related arsenates, vanadates and antimonates may be divided into three classes: (1) Anhydrous Phos phates , etc.; (2) Acid and Basic Phosphates, etc.; (3) Hydrous Phosphates, etc.

1. Anhydrous Phosphates, Etc.

Xenotime

Yttrium phosphate, YP04. Erbium may be present in consider able amount, also small amounts of cerium, silicon and thorium. Tetragonal. Crystal forms resemble those of zircon. In rolled grains. Prismatic cleavage. H. 4-5. G. 4.55-5.1. Vitreous to resinous luster. Color yellowish to reddish brown. Opaque. Infusible. Tests as in monazite, which see. A rare mineral which occurs, like monazite, as an accessory constituent in granite, gneiss and pegmatite veins. Found as rolled grains in the stream sands, particularly in Brazil.

Monazite

Composition. A phosphate of the cerium metals (Ce,La,Di)- P04 with usually some thorium silicate, ThSi04.

Crystallization. Monoclinic. Crystals usually small, often flattened parallel to the orthopinacoid.

Structure. Usually in granular masses, frequently as sand. Crystals rare.

Physical Properties. H. 5-5.5. G. 5. 2-5.3. Resinous luster. Color yellowish to reddish brown. Translucent to opaque.

Tests. Infusible. Insoluble in hydrochloric acid. After fusion with sodium carbonate, dissolve in nitric acid and add solu-

Tri Phy Lite — Lithiophilite

tion to excess of ammonium molybdate solution. A yellow precip itate forms (test for a phosphate) . Decomposed by heating with concentrated sulphuric acid; solution after dilution with water and filtering gives with ammonium oxalate a precipitate of the oxalates of the rare earths.

Occurrence. A comparatively rare mineral occurring as an acces sory mineral in granites, gneisses, aplites and pegmatites, and as rolled grains in the sands derived from the decomposition of such rocks, where it has been preserved because of its hardness and high specific gravity. Found in the United States, chiefly in North Carolina, both in gneiss and in the stream sands. The bulk of the world's supply of monazite sand comes from the provinces of Minas Geraes, Bahia, etc., Brazil.

Name. The name monazite is derived from a Greek word mean ing to be solitary, in allusion to the rarity of the mineral.

Use. Monazite is the chief source of thorium oxide, which it contains in amounts varying from 1 to 20 per cent; commercial monazite usually containing between 3 and 9 per cent. Thorium oxide is used in the manufacture of mantles for incandescent gas lights.

Triphylite — Lithiophilite

Phosphates of lithium with ferrous iron and manganese. Tri phylite corresponds to LiFePCh, Lithiophilite to LiMnP04. The two molecules are isomorphous and replace each other in varying amounts. Orthorhombic, crystals rare. Commonly massive, cleavable to compact. Cleavage parallel to base and brachypinacoid. H. 4.5-5. G. 3.42-3.56. Luster vitreous to resinous. Color bluish gray in triphylite to salmon-pink or clove-brown in lithio philite.' Translucent. Fusible at 2.5, giving red lithium flame. Triphylite becomes magnetic on heating in R. F. Lithiophilite gives in O. F. an opaque bluish green bead with sodium carbonate. Sol uble in nitric acid and when the solution is added to an excess of a solution of ammonium molybdate gives yellow precipitate (test for phosphoric acid). Rare minerals occurring in pegmatite veins asso ciated with other phosphates, etc. Triphylite found at Huntington, Massachusetts; Peru, Maine; Grafton, New Hampshire; Rabenstein, Bavaria; Finland. Lithiophilite found at Branchville, Connecticut.

Manual Of Mineralogy

The Apatite Group

The Apatite Group consists of a closely related series of minerals crystallizing in the pyramidal class of the hexagonal system. They are:

A patite, Ca4 (CaF) (P04) 3.

Pyromorphite,

Mimetite,

Vanadinite,

Apatite

Composition. Fluor-apatite, more rarely chlor-apatite,

Crystallization. .. Hexagonal: tri-pyramidal. Crystals usually long prismatic in habit; sometimes short prismatic or tabular.

Fig. 349.

Usually terminated by prominent pyramid of first order and frequently a basal plane (Figs. 348 and 349). Some crystals show faces of the third order pyramid and have at times a very complex development-

structure. Usually crystallized; also granular massive to compact.

Physical Properties. H. 5 (can just be scratched by a knife). G. 3.15. Vitreous to subresinous luster. Color usu ally some shade of green or brown; also blue, violet, colorless. Transparent to opaque.

Apatite

Tests. Difficultly fusible (5-5.5). Soluble in acids. Gives a yellow precipitate of ammonium phosphomolybdate when dilute nitric acid solution is added to large excess of ammonium molybdate solution. Concentrated hydrochloric acid solution gives white precipitate of calcium sulphate when a few drops of sulphuric acid are added. Recognized usually by its crystals, color and hardness. Distinguished from beryl by the prominent pyramidal terminations of its crystals and by its being softer than a knife.

Variety. Phosphorite. An impure variety of apatite is known as phosphorite. It occurs in a compact or earthy form or in con cretionary and nodular masses in fossiliferous rocks of different ages. Probably of organic origin.

Occurrence. Apatite is widely disseminated as an accessory con stituent in all classes of rocks; igneous, metamorphic and sedimen tary. If is also found in pegmatite and other veins, probably of pneumatolytic origin. Found in titaniferous magnetites. Occa sionally concentrated into large deposits or veins. In the form of phosphorite or phosphate rock occurs extensively as a rock stratum.

Apatite, as it exists scattered in small crystals throughout the rocks, slowly undergoes alteration and is gradually dissolved by percolating carbonated waters. Some of the phosphoric acid thus brought into solution goes into the sea where it is absorbed by living organisms; some remains in the soil, where its presence is a necessary condition for fertility and from which it is absorbed by plants and through them goes into the bodies of animals. The large bodies of phosphorite are derived from organic sources, such as animal remains. Bone is calcium phosphate in composition.

Apatite occurs in commercial amount in Ontario and Quebec, Canada. It is found there in crystals and masses enclosed in crys talline calcite and in veins and irregular nests along the contact of the limestone with eruptive rocks. The chief deposits lie in Ottawa County, Quebec. Crystalline apatite occurs in large amounts along the southern coast of Norway, between Langesund and Arendal. It is found there in veins and pockets associated with a mass of gabbro. Nodular deposits of phosphate rock are found at intervals all along the Atlantic coast from North Carolina to Florida, the chief deposits being in the latter state. High grade phosphate deposits are found in western middle Tennessee. Commercial de posits of phosphorite are to be found in northern France, Belgium, Spain, and especially in northern Africa, in Tunisia, Algeria and Morocco.

Finely crystallized apatite occurs at various localities in the Tyrol;

Manual Of Mineralogy

in Switzerland; Jumilla, Spain; at Auburn, Maine; St. Lawrence Co., New York; Alexander Co., North Carolina; San Diego Co., Califor nia, etc.

Use. Apatite and phosphate rock are chiefly used for fertilizer purposes. They are usually ground and treated with sulphuric acid to render the phosphoric acid more soluble. Transparent varieties of apatite of fine color are occasionally used for gem mate rial. The mineral is too soft, however, to allow of its very extensive use for this purpose.

Pyromorphite

Composition. Phosphorus pentoxide 15.7, lead protoxide 82.2, chlorine 2.6. The phosphorus is often re placed by arsenic and the species graduates into mimetite.

Crystallization. Hexagonal; tri-pyramidal. Prismatic crys tals with basal plane. Rarely shows pyramid truncations. Often in rounded barrel-shaped forms. Some times cavernous, the crystals being hollow prisms (Fig. 350). Frequently in parallel groups.

Structure. Crystallized, globular, reniform, fibrous and granular.

Physical Properties. H. 3.5-4. G. 6.5-7. 1. Resinous luster. Color usually various shades of green, brown, yellow; more rarely orange-yellow, gray, white. Subtransparent to nearly opaque.

Tests. Easily fusible (2). Gives a lead globule when fused on charcoal with sodium carbonate. When fused alone on charcoal gives a globule which on cooling shows crystalline structure. Faint white sub limate of lead chloride when heated in C. T. A few drops of the nitric acid solution added to ammonium molybdate solution gives a yellow precipitate of ammonium phosphomolybdate.

Occurrence. A mineral formed by secondary action and found in the upper oxidized portions of lead veins, associated with other

Vanadinite

lead minerals. Notable localities for its occurrence are the lead mines of Poullaouen and Huelgoat, Brittany; at Ems in Nassau; at Zschopau, Saxony; Pribram, Bohemia; Beresovsk, Ural Mts.; in Cumberland and at Leadhills, Scotland; Phcenixville, Pennsylvania; Davidson County, North Carolina; from Idaho, etc.

Name. Derived from two Greek words meaning fire and form in allusion to the crystalline form it assumes on cooling from fusion.

Use. A subordinate ore of lead.

Mimetite

Composition. Arsenic pentoxide 23.2, lead protoxide 74.9, chlorine 2.4. Phosphorus replaces the arsenic in part and calcium, the lead. Endlichite is a variety intermediate between mimetite and vanadinite.

Crystallization. Hexagonal; tri-pyramidal. Crystals pris matic, showing basal plane and at times pyramids. Usually in rounded barrel- to globular-shaped forms.

Structure. In rounded crystals, mammillary crusts.

Physical Properties. H. 3.5. G. 7-7.2. Resinous lus ter. Colorless, yellow, orange, brown. Subtransparent to almost opaque.

Tests. Easily fusible (1.5). Gives globule of lead when fused with sodium carbonate on charcoal. A fragment placed in C. T. and heated in contact with a splinter of charcoal gives deposit of metallic arsenic on walls of tube.

Occurrence. A comparatively rare mineral of secondary origin, occurring in the upper, oxidized portion of lead veins. Notable localities for its occurrence are in Cornwall and Cumberland, Eng land; Johanngeorgenstadt, Saxony; Nerchinsk, Siberia; Phcenixville, Pennsylvania; Eureka, Utah, etc.

Name. Derived from the Greek for imitator in allusion to its resemblance to pyromorphite.

Use. A minor ore of lead.

Vanadinite

Composition. Vanadium pentoxide 19.4, lead protoxide 78.7, chlorine 2.5. Phosphorus and arsenic some-

Manual Of Mineralogy

times present in small amount replacing vanadium. In the variety endlichite the proportion of V206 to As206 is nearly as 1 : 1.

Crystallization. Hexagonal; tri-pyramidal. Prism with base. Sometimes small pyramidal faces, rarely the pyramid of the third order. In rounded crystals; sometimes cavernous.

Structure. In crystals and globular forms. As incrustations.

Physical Properties. H. =3. G. 6.9-7. 1. Adamantine to resinous luster. Color ruby-red, brown, yellow. Transparent to opaque.

Tests. Easily fusible (1.5). Gives globule of lead on charcoal when fused with sodium carbonate. Gives an amber color in O. F. to salt of phosphorus bead (vanadium). Dilute nitric acid solution gives with silver nitrate a white precipitate of silver chloride. Endlichite would give in C. T. the reaction for arsenic (see under mimetite).

Occurrence. A rare mineral of secondary origin found in the upper oxidized portion of lead veins. Occurs in various districts in Arizona and New Mexico. Found in unusual crystals near Oudjda, Morocco.

Use. Source of vanadium and minor ore of lead. Vanadium is obtained chiefly from other ores, such as the sulphide, patronite; the vanadate, camotite; and a vanadium mica, roscoelite. Vanadium is used chiefly as a steel hardening metal. Metavanadic acid, HVOs, is used as a yellow pigment, known as va nadium bronze. Vanadium oxide is used as a mordant in dyeing.

Amblygonite

A phosphate of lithium and aluminum, having hydroxyl isomorphous with the fluorine and often sodium in small amount replacing the lithium. Triclinic. Usually massive, cleavable to compact. Perfect basal cleavage. H. =6. G. 3.08. Luster vitreous, pearly on cleavage face. Color white to pale green or blue. Translucent. Easily fusible (2) giving a red flame (lith ium). Insoluble in acids. After fusion with sodium carbonate and dissolving in nitric acid, solution with excess of ammonium molybdate solution gives yellow precipitate (test for phosphate). A

Vivianite

rare mineral found in pegmatite veins with tourmaline, lepidolite, apatite, etc. Found at Montebras, France; Hebron, Paris, Auburn, and Peru, Maine; Pala, California.

2. Acid And Basic Phosphates, Etc.

Olivenite

An arsenate and hydroxide of copper, Cu3A.S2O8.Cu (01 1) 2. Ortho rhombic. Prismatic, often in acicular crystals. Also reniform, fibrous, granular. H. 3. G. 4.1— 4.4. Fusible at 2-2.5. Ada mantine to vitreous luster. Color olive-green to blackish green; also shades of brown and yellow to white. Translucent to opaque. With sodium carbonate on charcoal gives a copper globule. When ignited in C. T. with sphnter of charcoal gives arsenical mirror. A little water when heated in C. T. Found rarely in oxidized portions of copper veins.

Lazulite

A phosphate of magnesium and aluminum, with varying amounts of ferrous iron, replacing the magnesium. Monoclinic, usually in steep pyramids. Also massive, granular to compact. H. 5-5.5. G. 3.05-3.1. Vitreous luster. Azureblue color. Translucent to opaque. Infusible. B. B. swells, loses its color and falls to pieces. Insoluble. A rare mineral.

3. Hydrous Phosphates, Etc.

Vivianite

Hydrous ferrous phosphate, Fe3P208.8H20. Monoclinic. Pris matic crystals, vertically striated; often in radiating groups; at times fibrous or earthy. Perfect pinacoidal cleavage. H. 1.5-2. G. 2.58-2.68. Vitreous to pearly luster. Colorless when un altered. Blue to green when altered. Transparent when fresh to opaque on exposure. Fusible at 2-2.5 to a magnetic globule. Nitric acid solution added to an excess of ammonium molybdate solution gives yellow precipitate (test for phosphate). Water in C. T. A rare mineral of secondary origin, associated with pyrrhotite, pyrite, limonite and other iron minerals.

Erythrite or Cobalt Bloom,' CosAs208.8H20, is a rare secondary mineral which occurs as an alteration product of cobalt arsenides. It is usually pulverulent in structure and crimson to pink in color. Annaberffite or Nickel Bloom, NijAs208.8H20, is a similar nickel compound. It is light green in color.

Manual Of Mineralogy

Scorodite

A hydrous ferric arsenate, FeAs04.2H20. Orthorhombic, usually in pyramidal crystals, resembling octahedrons; also prismatic. Crystals in irregular groups. Also earthy. H. 3.5-4. G. 3. 1-3.3. Vitreous luster. Pale green to liver-brown in color. Translucent. Fusible at 2-2.5. Magnetic when heated in R. F. Heated intensely with splinter of charcoal in C. T. gives arsenical mirror. Water in C. T. In hydrochloric acid reacts for ferric iron. Occurs in oxidized portions of metallic veins with arsenopyrite and other iron minerals.

Wavellite

A hydrous aluminum phosphate, Ortho rhombic, crystals rare. Usually in radiating globular aggregates. Good cleavage. H. 3-4. G. 2.33. Vitreous luster. Color white, yellow, green and brown. Translucent. Infusible. Insoluble. Decomposed by fusion with sodium carbonate and dissolved in nitric acid gives yellow precipitate (test for phosphoric acid) when solution is added to excess of ammonium molybdate. Moistened with cobalt nitrate, and then ignited assumes a blue color (aluminum). A rare mineral.

Turquois

Composition. A hydrous phosphate of aluminum, colored by small amounts of a copper phosphate, with isomorphous

Structure. Rarely in minute triclinic crystals, usually amor phous or cryptocrystalline. Massive compact, reniform, stalactitic, encrusting. In thin seams and disseminated grains.

Physical Properties. H. =6. G. 2. 6-2.8. Waxlike lus ter. Color blue, bluish green, green. Translucent to opaque.

Tests. Infusible. Insoluble. After fusion with sodium car bonate and dissolving in nitric acid, gives a yellow precipitate with an excess of ammonium molybdate solution (test for a phos phate). Gives a momentary green flame. In C. T. turns dark and gives water.

Occurrence. Turquois is a mineral of secondary origin, usually found in the form of small veins and stringers traversing more or less decomposed igneous rocks. The famous Persian deposits are

Soda Niter

found in trachyte near Nishapur in the province of Khorasan. In the United States it is found in a much altered trachytic rock in the Los Cerillos Mts., near Santa Fe, New Mexico; elsewhere in New Mexico. Turquois has also been found in Arizona, Nevada and California.

Name . Is French and means Turkish, the original stones having come into Europe through Turkey.

Use. As a gem stone. It is always cut in round or oval forms. Much turquois is cut which is veined with the various gangue materials and such stones are sold under the name of turquois matrix.

Nitrates

Soda Niter

Composition. Sodium nitrate, NaN03 Nitrogen pentoxide 63.5, soda 36.5.

Crystallization. Hexagonal-rhombohedral. Homceomorphous with calcite. Has closely the same crystal constants, cleav age, optical properties, etc., as calcite. If a cleavage block of calcite is placed in a crystallizing solution of sodium nitrate, small rhombohedrons of the latter will form with parallel orientation on the calcite.

Structure. Usually massive, as an incrustation or in beds.

Physical Properties. Perfect rhombohedral cleavage. H. 1.5-2. G. 2.29. 'Vitreous luster. Colorless or white, also reddish brown, gray, yellow, etc. Transparent to opaque. Cool ing taste.

Tests. Very easily fusible (1), giving a strong yellow sodium flame. After intense ignition gives an alkaline reaction on mois tened test paper. Easily and completely soluble in water. Heated in C. T. with potassium bisulphate gives off red vapors of nitrous oxide.

Occurrence. Because of its solubility in water it is only to be found in arid and desert regions. Found in large quantities in the provinces of Tarapacd and Antofagasta, northern Chile, and the neighboring parts of Bolivia. Occurs over immense areas as a salt (caliche) bed interstratified with sand, beds of common salt, gypsum,

Manual Of Mineralogy

etc. Has been noted in Humboldt County, Nevada, and in San Bernardino County, California.

Use. In Chile it is quarried, purified and used as a source of nitrates.

Niter

Potassium nitrate, KN03. Orthorhombic. Usually as thin en crustations or as silky acicular crystals. Perfect cleavage. H. 2. G. 2.09-2.14. Vitreous luster. Color white. Translucent. Easily fusible (1) giving violet flame (potassium). After ignition gives alkaline reaction on moistened test paper. Heated in C. T. with potassium bisulphate gives red fumes of nitrous oxide. Easily soluble in water. Saline and cooling taste. Found as delicate crusts, as an efflorescence, on surfaces of earth, walls, rocks, etc. Found as' a constituent of certain soils. Also in the loose soil of limestone caves. Not as common as soda niter, but produced from soils in Spain, Italy, Egypt, Arabia, Persia, and India. Used as a source of nitrogen compounds.

Borates

Boracite

Composition, Mg7Cl2BI603o. Isometric; tetrahedral. Crystals usually show cube, tetrahedron and dodecahedron in some com bination. Crystals usually isolated and disseminated in other minerals. Also massive. Vitreous luster. Colorless, white, gray, green. Transparent to translucent. H. =7. G. 2.9-3.0. Fus ible at 3 with green flame color (boron). Soluble in hydrochloric acid. Turmeric paper moistened with a solution of the mineral and then dried at 100° C. turns reddish brown (boron). Occurs asso ciated with halite, anhydrite, gypsum, etc., as one of the products formed by the evaporation of bodies of salt water.

Colemanite

Hydrous borate of calcium, Ca2B60u.5H20. Monoclinic, in short prismatic crystals, highly modified. Cleavable massive to granular and compact. Perfect pinacoidal cleavage. H. 4-4.5. G. 2.42. Vitreous to adamantine luster. Colorless to white. Transparent to translucent. Fusible at 1.5. B. B. exfoliates, crumbles and gives green flame (boron). Water in C. T. A rare mineral, but occurring in considerable quantity in the salt lake de posits, in the arid regions of southeastern California, in Death Valley, Inyo County, and in San Bernardino and Los Angeles counties.

Uraninite

Borax

Composition. Hydrous sodium borate, Na2B4O7.10H2O Boron trioxide 36.6, soda 16.2, water 47.2.

Crystallization. Monoclinic. Prismatic crystals, sometimes quite large.

Structure. In crystals and as massive cellular material or encrustations.

Physical Properties. Perfect cleavage parallel to orthopinacoid. H. 2-2.5. G. 1.75. Vitreous luster. Colorless or white. Translucent to opaque. Sweetish-alkaline taste.

Tests. Easily fusible (1-1.5) with much swelling and gives strong yellow flame (sodium). Readily soluble in water. Tur meric paper, moistened with a dilute hydrochloric acid solution of the mineral, turns reddish brown when dried at 100° C. Much water in C. T.

Occurrence. Formed as a deposit from the evaporation of salt lakes, and as an efflorescence on the surface of the ground in arid regions. The deposits in Tibet have furnished large amounts of borax, which has been exported to Europe in the crude state, under the name of tincal. Found in quantity in the United States in the desert region of southeastern California, in Death Valley, Inyo County and in San Bernardino County. Occurs also in the adjacent parts of Nevada. Borax is associated with the other minerals deposited in similar manner, such as halite, gypsum, colemanite, and various rare borates.

Name. Borax comes from an Arabic name for the substance.

Use. Borax is used for washing and cleansing; as an anti septic, preservative, etc., in medicine; as a solvent for metallic oxides in soldering and welding; and as a flux in various smelting and laboratory operations.

Uranates

Uraninite. Pitch Blende

Composition. An uncertain combination of the oxides of uranium, U03 and U02. With small amounts of lead and the rare elements, thorium, yttrium, cerium, nitrogen, helium, argon,

Manual Of Mineralogy

radium. It is the mineral in which the gas helium was first dis covered on the earth, having been previously noted in the gases surrounding the sun by means of the sun's spectrum. In it, also, was first discovered the rare and strange substance, radium.

Crystallization. Isometric. In octahedrons, also with do decahedrons. Less often showing cube faces. Crystals rare.

Structure. Usually massive and botryoidal; also in grains.

Physical Properties. H. 5.5. G. 9-9.7 (unusually high). Luster submetallic to pitchlike, dull. Color black. Streak brownish black.

Tests. Infusible. Imparts to the salt of phosphorus bead in 0. F. a yellowish green and in R. F. a green color. Soluble in dilute sulphuric acid with the slight evolution of helium gas. Characterized chiefly by its pitchy luster, its high specific gravity, its color and streak.

Occurrence. Occurs either as a primary constituent of granite rocks or as a secondary mineral with ores' of silver, lead, copper, etc. Found under the latter condition at Johanngeorgenstadt, Marienberg and Schneeberg in Saxony, at Joachimsthal and Pribram in Bohemia, and Rezbanya in Rumania. Occurs in Norway. In the United States found in isolated crystals in pegmatite veins at Middletown, Glastonbury and Branchville, Connecticut. In the mica mines of Mitchell County, North Carolina. A narrow vein of it has been mined near Central City, Gilpin County, Colorado.

Use. The chief interest in the mineral lies in the fact that it is the principal source of radium. This element exists in it in ex tremely small percentages and it is necessary to subject a large amount of the mineral to a chemical concentration in order to produce a few grains of a radium salt. Uranium, itself, has only a limited use. Experiments have been made looking toward its use in steel. In the form of various compounds it has a limited use in coloring glass and porcelain, in photography and as chemical reagents.

Sulphates

The sulphates and the related chromates may be divided into three divisions: (1) Anhydrous Sulphates; (2) Acid and Basic Sulphates; (3) Hydrous Sulphates.

Barite

1. Anhydrous Sulphates

Glaub erite

A sulphate of sodium and calcium, Monoclinic. Crystals thin, tabular parallel to base. Basal cleavage. H. 2.5-3. G. 2.7—2.85. Vitreous luster. Color pale yellow or gray. Slightly saline taste. Fusible (1.5-2), giving yellow flame (sodium). After ignition, gives an alkaline reaction on moistened test paper. Soluble in hydrochloric acid and solution with barium chloride gives white precipitate of barium sulphate. A rare mineral occurring in the saline deposits, formed by the evaporation of salt lakes.

Barite Group

The Barite Group consists of the sulphates of barium, stron tium, lead and calcium. They crystallize in the orthorhombic system with closely related crystal constants and similar habits. The members of the group are as follows:

Barite, BaS04.

Celestite, SrS04.

Angledte, PbS04.

Anhydrite, CaS04.

Barite. Barytes. Heavy Spar

Composition. Barium sulphate, BaS04 Sulphur trioxide 34.3, baryta 65.7. Strontium and calcium sulphates present at times.

Crystallization. QPfHombic. Crystals usually tabular par allel to base; often diamond shaped because of the presence of a short prism (Fig. 351). Both macro- and brachydomes usually present, either beveling the comers of the diamond-shaped crystals (Figs. 352 and 353), or, if the prism faces are wanting, beveling the edges of the tables and forming rectangular prismatic-shaped crystals elongated parallel to either the brachy- or macro-axis (Figs. 354 and 355). Crystals sometimes quite complex.

Structure. In crystals. In divergent groups of tabular crys tals forming "crested barite." Also coarsely laminated; granular, earthy.

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Physical Properties. Perfect cleavage parallel to base and prism faces. H. 3-3.5. G. 4.5 (heavy for a nonmetallic mineral). Vitreous luster; pearly at times on base. Colorless, white, and light shades of blue, yellow, red. Transparent to opaque.

Pig. 352. Fig. 353.

Tests. Fusible at 4, giving yellowish green barium flame. After ignition gives an alkaline reaction on moistened test paper. Fused with sodium carbonate and charcoal dust gives a residue, which, when moistened, produces a dark stain of silver sulphide on a clean silver surface. Recognized by its white color, high specific gravity, characteristic cleavage and crystals.

Occurrence. Barite is a common mineral of wide distribution. It occurs usually as a gangue mineral in metallic veins, associated especially with ores of silver, lead, copper, cobalt, manganese and antimony. Sometimes in veins in limestone with calcite and celestite or in sandstone with copper ores. At times acts as a cement in sandstone. Deposited occasionally as a sinter by waters from hot springs. Notable localities for the occurrence of crystalline barite are in Westmoreland, Cornwall, Cumberland, and Derbyshire, England; Felsobanya and other localities, Rumania; in Saxony and Bohemia. In the United States at Cheshire, Connecticut; Dekalb, New York; Fort Wallace, New Mexico. Massive barite, occurring usually as veins, nests and irregular bodies in limestones, has been quarried in the United States in Georgia, Tennessee, Missouri, etc.

Celestite

Use. Barite is used chiefly for the production of barium hy droxide, employed in the refining of sugar. It is ground and used as a white pigment; to give weight to cloth and paper, etc.

Celestite

Composition. Strontium sulphate, SrS04 Sulphur trioxide 43.6, strontia 56.4.

Crystallization. Orthorhombic. Crystals resemble closely those of barite (which see). Commonly tabular parallel to the base or prismatic parallel to the brachy- or macro-axis with prominent development of the domes (Fig. 356). Crystals which are elongated parallel to the brachy-axis are frequently terminated in front by four faces in nearly equal development, consisting of 2 prism faces and 2 of the macrodome (Fig. 357) .

Fig. 356.

Fig. 357.

Structure. Crystallized. Also radiating fibrous; sometimes granular.

Physical Properties. Perfect cleavage parallel to base and prism. H. 3-3.5. G. 3.95-3.97. Luster vitreous to pearly. Colorless, white, often faintly blue or red. Transparent to translucent.

Tests. Fuses at 3.5-4 and colors the flame crimson (stron tium). After ignition gives an alkaline reaction on moistened test paper. Fused with sodium carbonate and charcoal dust gives a residue, which, when moistened, produces on a clean silver surface a dark stain of silver sulphide. Closely resembles barite and it will usually need a flame test to positively differentiate the two species.

Manual Of Mineralogy

Occurrence. Celestite is found usually disseminated through limestone or sandstone, or in nests and lining cavities in such rocks. Associated with calcite, dolomite, gypsum, halite, sulphur, etc. Notable localities for its occurrence are with the sulphur deposits of Sicily; at Bex, Switzerland; Yate, Gloucestershire, England; Herrengrund, Slovakia; Strontian Island, Put-in-Bay, Lake Erie; Min eral County, West Virginia; from Lampasas, Texas; Inyo County, California.

Name. Derived from caelestis in allusion to the faint blue color often present.

Use. Used in the preparation of nitrate of strontium for fire works. Other strontium salts used in the refining of sugar.

Anglesite

Composition. Lead sulphate, PbS04 Sulphur trioxide 26.4, lead oxide 73.6.

Crystallization. Orthorhombic. Crystal habit often similar to that of barite (which see) but much more varied. Crystals may be prismatic parallel to all three of the crystal axes and frequently show many forms, with a complex development.

Structure. Crystallized. Also massive, granular to compact. Frequently earthy, in concentric layers about a nucleus of galena.

Physical Properties. Perfect cleavage parallel to base and prism. H. 2.75-3. G. 6.12-6.39 (unusually high). Ada mantine luster when pure and crystalline, dull when earthy. Colorless, white, pale shades of yellow, green and blue. May be colored dark gray, etc., by impurities. Transparent to opaque.

Tests. Easily fusible at 2.5. On charcoal with sodium car bonate reduced to a lead globule with yellow to white coating of lead oxide. Fused with sodium carbonate and charcoal dust gives a residue, which, when moistened, produces on a clean silver surface a dark stain of silver sulphide. Recognized by its high specific gravity, its adamantine luster and frequently by its association with galena.

Occurrence. Anglesite is a common lead mineral of secondary origin. It is formed through the oxidation of galena, sometimes directly to the sulphate as is shown by the concentric layers of angle-

Anhydrite

site found at times surrounding a core of unaltered galena, or some times by an intermediate solution and subsequent recrystallization. Found in the upper, oxidized portions of lead veins, associated with galena, cerussite, sphalerite, smithsonite, calamine, iron oxides, etc. Notable localities for its occurrence are Monte Poni, Sardinia; Is land of Anglesey, Wales; from Derbyshire; at Leadhills, Scotland, f rom Sidi-Amor-ben-Salem in Tunis; near Otavi, South West Africa; Broken Hill, New South Wales; Dundas, Tasmania. Occurs in the United States at Phcenixville, Pennsylvania; Tintic district, Utah; Cceur d'Alene district, Idaho.

Name. Named from the original locality on Island of Anglesey. Use. An ore of lead.

Anhydrite

Composition. Anhydrous calcium sulphate, CaS04 Sulphur trioxide 58.8, lime 41.2.

Crystallization. Orthorhombic. Crystals rare; when ob served are thick tabular, also prismatic parallel to the macro-axis.

Structure. Usually in crystalline masses, with rectangular cleavage. Fibrous, granular.

Physical Properties. Cleavage parallel to the three pinacoids, so yielding rectangular blocks. H. 3-3.5. G. 2.89-2.98. Luster vitreous to pearly. Color white with sometimes a faint gray, blue or red tinge. Transparent to translucent.

Tests. Fusible at 3-3.5. After ignition gives an alkaline re action on moistened test paper. Moistened with hydrochloric acid and ignited gives orange-red flame of calcium. Soluble in hot hydrochloric acid and dilute solution with barium chloride gives white precipitate of barium sulphate.

Occurrence. Occurs in much the same manner as gypsum, and often associated with that mineral but is not nearly as common. Found in beds associated with salt deposits and in limestone rocks. Found at times in amygdaloidal cavities in basalt. Occurs at Wieliczka, Poland; Aussee in Styria; at Stassfurt, Prussia; Bavaria; Hall in Tyrol; Bex, Switzerland; in the United States at Lockport, New York; Nashville, Tennessee. Found in large beds in Nova Scotia.

Manual Of Mineralogy

Crocoite

Lead chromate, PbCr04. Monoclinic. In slender prismatic crys tals, vertically striated. Also granular. H. 2.5-3. G. 5.9- 6.1. Adamantine luster. Color bright red. Orange-yellow streak. Fusible at 1.5. Fused with sodium carbonate on charcoal gives a lead globule. With borax gives a green bead in O. F. A rare min eral found in the oxidized zones of lead veins. Fine crystals come from Mount Dundas, Tasmania.

2. Acid And Basic Sulphates

Brochantite

A basic sulphate of copper, Orthorhombic. Slender prismatic crystals, vertically striated, often acicular. Some times massive reniform. Perfect pinacoidal cleavage. H. 3.5—4. G. 3.9. Vitreous luster. Emerald to blackish green in color. Transparent to translucent. Fusible (3.5). Copper globule when fused with sodium carbonate on charcoal. Hydrochloric acid solu tion with barium chloride gives white precipitate of barium sul phate. Water in C. T. A rare mineral found in the oxidized portions of copper veins.

3. HYDROUS SULPHATES Gypsum. Selenite

Composition. Hydrous calcium sulphate, CaS04.2H20 Sulphur trioxide 46.6, lime 32.5, water 20.9.

Crystallization. Monoclinic. Crystals usually tabular paral lel to clinopinacoid; in diamond-shaped crystals with edges beveled by prism and pyramid faces (Fig. 358). Other forms rare. Sometimes twinned (Fig. 359).

Structure. Cleavable massive; foliated; granular massive; sometimes with fibrous appearance.

Physical Properties. Cleavage in three directions; perfect parallel to clinopinacoid, yielding easily thin folia; with conchoidal surface parallel to orthopinacoid; with fibrous fracture parallel to a pyramid. H. 2 (can be scratched by the finger nail). G. 2.32. Usually with vitreous luster; sometimes

Gypsum

silky. Colorless, white, gray; sometimes various shades of yel low, red, brown, etc., from impurities. Transparent to opaque.

Tests. Fusible at 3-3.5. After intense ignition, residue gives alkaline reaction on moistened test paper. Soluble in hot dilute hydrochloric acid and solution with barium chloride gives white precipitate of barium sulphate. Much water in C. T. Charac terized by its softness and its perfect pinacoidal cleavage.

Fig. 358.

Fig. 359.

Varieties. Crystalline. In crystals or foliated masses.

Fibrous. With coarse to fine fibrous appearance. Satin spar is fine fibrous with silky luster.

Massive. Alabaster, a fine-grained variety. Rock gypsum, massive granular or earthy; often impure.

Occurrence. Gypsum is a common mineral which is widely dis tributed in sedimentary rocks, often as thick beds. It frequently occurs interstratified with limestones and shales. Usually to be found as a layer underlying beds of rock salt and has been deposited there as one of the first minerals to crystallize because of the concen tration of salt waters. Occurs also as lenticular bodies or scattered crystals in clays and shales. Commonly of primary origin but may have been derived from the alteration of anhydrite. Found at times in volcanic regions, especially where limestones have been acted upon by sulphur vapors. Also, is common as a gangue mineral in metallic veins. Associated with many different minerals, the more common ones being salt, anhydrite, dolomite, calcite, sulphur, pyrite, quartz. Deposits of gypsum of commercial importance are found in many localities in the United States, but the chief producers are located in New York, Oklahoma, Texas, Iowa, Michigan, Ohio, Kansas and

Manual Of Mineralogy

Nevada. Gypsum is found in large deposits in Arizona and New Mexico in the form of wind-blown sand.

Name. Derived from the Greek name for the species. At times the crystalline variety is called selenite, which comes from a Greek word meaning moon, probably in allusion to the moon-like white reflections from some varieties.

Use. Gypsum is chiefly used for the production of plaster of Paris. In the manufacture of this material, the gypsum is ground and then heated, until a large proportion of the water has been driven off. This plaster, when mixed with water, slowly absorbs the water and so hardens or "sets." Plaster of Paris is used ex tensively for "staff," the material from which temporary exposition buildings are built, and for molds and casts of all kinds. Gypsum is employed in making adamant plaster for interior use. Serves as land plaster, for a fertilizer. Satin spar and alabaster are cut and polished for various ornamental purposes but are restricted in their uses on account of their softness.

Chalcanthite. Blue Vitriol

Composition. Hydrous copper sulphate, CuS04.5H20 Sulphur trioxide 32.1, cupric oxide 31.8, water 36.1.

Crystallization. Triclinic. Crystals commonly tabular paral lel to a pyramid face.

Structure. Crystallized, also massive in stalactitic and reniform structure, sometimes with fibrous appearance.

Physical Properties. H. 2.5. G. 2.12-2.30. Vitreous luster. Color deep azure-blue. Transparent to translucent. Metallic taste.

Tests. Fusible at 3. Gives copper globule when fused with sodium carbonate on charcoal. Soluble in water. Dilute hydro chloric acid solution gives with barium chloride precipitate of barium sulphate. Much water in C. T. Characterized by its blue color and its solubility in water.

Occurrence. A rare mineral, found at times in arid regions as a secondary mineral, occurring near the surface in copper veins, and derived from the original copper sulphides by oxidation. Often deposited from the waters in copper mines.

Wolfram I Te-Hu Bn Erite

Use. A minor ore of copper. The artificial blue vitriol is used in calico printing, in galvanic cells, and in various manufacturing industries.

Kalinite. Potash Alum

A hydrous sulphate of aluminum and potassium, K2S04. Isometric. Usually fibrous or massive. H. 2- 2.5. G. 1.75. Vitreous luster. Colorless to white. Trans parent to translucent. Fuses at 1 with swelling and gives a violet flame (potassium). Easily soluble in water. Astringent taste. Hydrochloric acid solution with barium chloride gives a white pre cipitate of barium sulphate, and with ammonium hydroxide in excess gives white precipitate of aluminum hydroxide. A com paratively rare mineral, which usually occurs as efflorescence on clays and slates, particularly those containing disseminated pyrite. Also at times in connection with sublimation products from vol canoes.

TUNGSTATES, MOLYBDATES Wolf ramite-Hubnerite

Composition. Tungstates of ferrous iron and manganese. Wolframite in which the ratio of the iron to the manganese varies from 9:1 to 2:3. Hubnerite, nearly pure MnW04.

Crystallization. Monoclinic. Crystals commonly tabular parallel to the orthopinacoid, giving bladed forms. Prism zone vertically striated.

Structure. In bladed, lamellar or columnar forms. Massive granular.

Physical Properties. Perfect cleavage parallel to clinopinacoid. H. 5-5.5. G 7.2-7.5. Submetallic to resinous lus ter. Color black in wolframite to brown in hubnerite. Streak from nearly black to brown.

Tests. Fusible (3-4). Insoluble in acids. Fused with sodium carbonate, fusion then dissolved in hydrochloric acid, tin added and solution boiled gives a blue color (tungsten). In 0. F. with sodium carbonate gives bluish green bead (manganese). Wolfram ite when fused with sodium carbonate in R. F. on charcoal gives a magnetic mass.

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Occurrence. Comparatively rare minerals, found usually in granite and pegmatite veins, having been formed under pneumatolytic conditions. Also deposited in sulphide veins. Commonly found with cassiterite and associated also with scheelite, bismuth, quartz, pyrite, galena, sphalerite, etc. Found in fine crystals from Schlaggenwald, Bohemia, and in the various tin districts of Saxony and Cornwall. Important deposits occur in Burma, New South Wales, Bolivia. Wolframite occurs in the United States in the Black Hills, South Dakota; Boulder County, Colorado. Hubnerite is found near Silverton, Colorado; Mammoth district, Nevada; Black Hills, South Dakota.

Use. Chief ores of tungsten. Tungsten is used as a hardening metal in the manufacture of tool steel. Also as a filament in incandescent electric lights. Sodium tungstate is used in fire proofing cloth and as a mordant in dyeing.

Scheelite

Composition. Calcium tungstate, CaW04 Tungsten trioxide 80.6, lime 19.4. Molybdenum is usually present, replacing a part of the tungsten.

Crystallization. Tetragonal; tri-pyramidal. Crystals usually simple pyramids of first order. Closely resemble isometric octahe drons in angles (Fig. 360). Faces of the pyramid of third order are small and rare.

Structure. Massive granular; in crys tals.

Physical Properties. Cleavage parallel to pyramid of first order. H. 4.5-5. G. 6.05 (unusually high for a mineral with nonmetallic luster). Vitreous to ada mantine luster. Color white, yellow, green, brown. Usually translucent to opaque, sometimes transparent.

Tests. Difficultly fusible (5). Decomposed by boiling hydro chloric acid leaving a yellow residue of tungstic oxide, which, when tin is added to the solution and boiling continued, turns first blue then brown. Recognized by its high specific gravity and the test for tungsten.

Wulfenite

Occurrence. Formed under pneumatolytic conditions and is found in pegmatite veins or ore veins which are associated with granitic rocks. Associated with cassiterite, topaz, fluorite, apatite, molybdenite, wolframite, etc. Found at times with gold. Occurs in connection with the tin deposits of Bohemia, Saxony and Cornwall; in quantity in New South Wales and Queensland. Found in the United States at Trumbull, Connecticut; San Bernardino County, California; near Dragoon, Cohise County, Arizona; at Lead, South Dakota; from Leadville, Colorado.

Use. A subordinate ore of tungsten, wolframite (which see) furnishing the greater amount. Tungsten is used chiefly as a steel-hardening metal.

Wulfenite

Composition. Lead molybdate, PbMo04 Molybdenum tri oxide 39.3, lead oxide 60.7. Calcium sometimes replaces the lead.

Crystallization. Tetragonal; tri-pyramidal. Crystals usually square tabular in habit with prominent base. Sometimes very thin. Edges of tables beveled with faces of low second order pyramid. More rarely pyramidal in habit. Pyramid of third order in small faces and very rare.

Structure. In crystals; also massive granular, coarse to fine.

Physical Properties. H. 4.5-5. G. 6.05. Vitreous to adamantine luster. Color yellow, orange, red, gray, white. White streak. Transparent to subtranslucent.

Tests. Easily fusible at 2. Gives a lead globule when fused with sodium carbonate on charcoal. With salt of phosphorus in R. F. gives green bead; in 0. F. yellowish green when hot to almost colorless when cold. If powdered mineral is moistened with concentrated sulphuric acid and evaporated almost to dryness in a porcelain crucible the residue will show a deep blue color on cooling (molybdenum).

Occurrence. Found in the oxidized portion of lead veins with other ores of that metal, especially vanadinite and pyromorphite. Found in the United States at Phoenixville, Pennsylvania; in a number of places in Utah, Nevada, Arizona and New Mexico.

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Use. An ore of molybdenum. Molybdenum is used as a steel-hardening metal. In the form of ammonium molybdate it is used as a chemical reagent, as a fireproofing material and as a disinfectant. Molybdenum used also to color leather and rubber.

Lists Of Minerals Arranged According To Elements

In the following section are given lists of the minerals that are of commercial importance because of some element which they con tain. All of the minerals that could serve as a source of any particular element are grouped together, their relative importance being indicated by the type used in printing their names. The order in which the minerals are given in each list is the same as that in which they are described in the previous section of this book. The different elements have been treated in alphabetical sequence in order to facilitate ready reference to them. Each table will be followed by a brief general discussion of the occurrence of the minerals given in it and by a short statement as to the uses of the element derived from them.

Aluminum

Cryolite, Na3AlF6. Bauxite,

Corundum, A1203. The Feldspars, KAlSi308, NaAlSi308,

CaAl2Si203, etc.

Gibbsite, Kaolin, HiAliSi*0.

Aluminum is the most common of all the metals. Unlike other metals, however, its occurrence, with the exception of the fluorides, is restricted to minerals containing oxygen. It is most abundantly found in the rock-making silicates, in the majority of which it is an essential constituent. It also occurs in large amount in the clays. The minerals which can be used as ores of the metal are, however, few in number, the only one at present of importance being bauxite. The enormous amounts of aluminum contained in the various silicates are not yet available because of the difficulty and expense of extraction.

Aluminum

Bauxite is produced in the United States chiefly from Arkan sas, Alabama, Georgia and Tennessee. The deposits in Arkansas are found in Pulaski and Saline counties. They have an average thickness of 10 to 15 feet. In one district the beds lie directly upon a body of kaolin, which in turn rests upon a syenite rock-mass and it is probable that both minerals have been derived from its de composition. The Alabama-Georgia district extends from Jack sonville, Alabama, to Cartersville, Georgia. The ore occurs as pockets or lenses in a clay which has been derived by weathering processes from a dolomite limestone. The bauxite is either pisolitic or clay-like in structure.

Cryolite, imported from Greenland, has been used as an ore of aluminum and at present is used as a flux in the electrolytic process by which most of the metal is obtained.

The usual process at present by which aluminum is extracted from the bauxite ores is briefly as follows: The ore is heated to low redness with sodium carbonate forming sodium aluminate. This compound is leached out by water and by passing C02 gas into the solution the aluminum is precipitated as the hydroxide. The latter on being heated is converted into the oxide of the metal. The pure metal is prepared from this oxide by an electrolytic process which takes place in a bath of fused cryolite. The tank in which the reaction takes place is lined with carbon and forms the cathode, while graphite rods suspended in the bath serve as the anode. The metal collects in the bottom of the tank.

Aluminum is valuable because of its low density and because it is not easily oxidized or corroded. It is a good electrical conductor and to some extent is replacing copper used for that purpose. It is used in many alloys, particularly with zinc, copper and nickel. Duraluminum is the trade name of the most important alloy. It is used in small amounts in casting steel in order to take up any oxygen in the melt and also to prevent porosity in the metal. Aluminum and iron oxide are mixed in a finely divided state to form the material known as thermite. When this mixture is ignited the heat of the combustion of the aluminum is so great that it can be used in welding iron and steel. Sheets and tubes and castings of aluminum are used wherever a light weight metal is

Manual Of Mineralogy

desired, for instance in the manufacture of certain parts of auto mobiles. Aluminum is used in the manufacture of cooking uten sils, as a substitute for lithographic stones and zinc plates, as powder in the manufacture of metallic paints, etc. It is used also in the form of salts, chiefly alum and aluminum sulphate, to harden paper, in the purification of water, as mordants in dyeing, in baking pow ders, in medicine, etc.

Antimony

Native Antimony, Sb. Stibnite, Sb2S3.

Antimony occurs in a considerable number of minerals, espe cially those belonging to the series known as the sulpho-salts, which are largely combinations of copper, lead or silver with antimony and sulphur. These minerals are mined, however, for the other metals that they contain and any antimony that is produced from them is in the nature of a by-product. Stibnite is practically the only mineral which is mined for its antimony. This mineral has been found in the United States in a comparatively few deposits. It has been mined on a small scale in California, Nevada and Idaho. The greater part of the antimony produced in the United States is derived from antimonial lead which is an alloy of the two metals derived from the smelting of lead ores that contain small amounts of antimony minerals. Considerable amounts of antimony and antimony ores are imported, chiefly from Chinn, .-Franco- Italy, Mexico and Japan.

Antimony is used in alloys, such as type metal (lead, antimony and bismuth), babbitt or anti-friction metal (antimony, tin, etc.), britannia metal (tin with antimony and copper), etc. Antimony oxide is used as a pigment and in the glazing of enameled ware. The sulphide is used in fireworks, in safety matches and in percus sion caps and in vulcanizing rubber. Other compounds are used in medicine and for various purposes in the arts.

Arsenic

Native Arsenic, As. Realgar, AsS.

Orpiment, As2S3. Arsenopyrite, FeAsS.

Bismuth

Arsenic in minerals ordinarily plays the part of a nonmetallic element, similar to sulphur in its chemical relations. It forms three classes of compounds, the arsenides, the sulpharsenites and the arsenates. The number of minerals which contain arsenic is considerable but only a few can be considered as distinctively arsenic minerals. Arsenopyrite is the only one which at present serves as an ore. Most of the arsenic oxide produced comes as a by-product in the smelting of arsenical ores for copper, gold, lead, etc. Large amounts of the oxide are obtained from the smelting of the copper ores at Blllte-Mont., the mineral enargite, CuaAsS*, being its chief source. The oxide is also produced at smelting plants in Washington and Utah. Arsenopyrite has been mined .t. Rrinton, Virginia.

'Metallic arsenic is used in some alloys, particularly with lead in shot metal. Arsenic is chiefly used, however, in the form of white arsenic, or arsenious oxide. This is employed in medicine, as a poison, as a preservative, in making Paris green (an arsenate and acetate of copper), as a pigment, in glass manufacture, etc.

Barium

Witherite, BaC03. Barite, BaS04.

Barite is the chief source of barium compounds. It has been mined in the United States in Mjsmir.i North Carolina, Georgia, Kentucky and Tennessee. The mineral is ground and sometimes purified by washing and then used as a partial substitute for white lead in paint, to give weight to paper and cloth, etc. Barium hydroxide _js used extensively in sugar refining.

Bismuth

Native Bismuth, Bi. Bismuthinite, Bi2S3.

The most important bismuth mineral is the native metal. Bismuth is produced, however, mostly as a by-product in the smelting of gold and silver ores. Only a comparatively small amount is obtained in the United States, chiefly from Colorado and Utah.

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Bismuth is used in the alloys which it forms with lead, tin and cadmium. These fuse at low temperatures and are used for safety fuses, safety plugs, etc. Various compounds of bismuth are used in medicine and in the arts.

Cadmium

Greenockite, CdS.

Greenockite is the only cadmium mineral of importance and this is very rare in occurrence. The cadimum of commerce is obtained from zinc ores that carry a small amount of the metal. Practically the entire output of cadmium in the United States comes from the zinc ores of the Joplin district, Missouri, which frequently contain some 0.3 per cent of the metal. The zinc ores of Silesia have for a long time been a prominent source of cadmium.

Cadmium is used in various alloys, such as low-fusing alloys, denial amalgam, metal for stereotype plates, etc. The metal is used witlTsiiver in electroplating. The sulphide, CdS, is known as cadmium-yellow and is used extensively as a pigment. Various salts oFcadmium hnd uses in the arts. - -

Chromium

Chromite, FeCr04 with MgCr04. Crocoite, PbCr04.

Chromite, or chromic iron ore, is the chief source of chromium. Its production in the United States is very small, coming mostly from Shasta County, California. . It has also been found in work able deposits in Pennsylvania, Maryland, North Carolina and Wyoming. Large amounts of the ore are imported from British South Africa; Portugese East Africa; Greece; India; and Cuba.

Chromium is used as a steel-hardening metal. It gives to steel a superior hardness and if added in the proper proportion does not produce brittleness. Chromium is used in plating and in certain non-iron alloys. The mineral chromite is made into bricks that are used as linings for metallurgical furnaces. Various red, orange and green pigments and dyes are made from chromium compounds. Chromium salts are used as mordants in the dyeing and printing of cloth. Chromium compounds are useful in tanning leather.

Copper

Cobalt

Linnaeite, Co3S4. Cobaltite, CoSAs.

Smaltite, CoAs2.

Cobalt is a rare element which is usually found in small amounts associated with nickel minerals. Much of the cobalt of commerce is produced from other ores as a by-product. The United States produces little or no cobalt. The metal is produced from ores found in Queensland, Australia; the Belgian Congo; and also from the silver ores of Cobalt , Canada.

Cobalt is to some extent used in high speed steels and in an alloy with chromium and tungsten, known as stellite. Also used in the form of the oxide as a blue pigment in making glass and pottery.

Native Copper, Cu. Chalcocite, Cu2S. Stromeyerite, CuAgS. Covellite, CuS. Enargite, Cu*AsS4. Atacamite, Cuprite, Cu20.

Copper

Bornite, Cu6FeS4. Chalcopyrite, CuUeS2. Tetrahedrite, Cu8Sb2S7. Tennantite, CugAs2S7. Chrysocolla, CuSi03.2H20. Olivenite, Brochantite,

Malachite, Chalcanthite, CuS04.5H20. Azurite,

Copper is a common and widely distributed element. It is found in a number of important minerals which usually occur in veins. Chalconvritp is the most, important ore, and in most cases is the only primary copper mineral in a deposit. The other im portant sulphides, bornite and chalcocite, are usually, although not always, the results of secondary enrichment. Solutions that have leached out the copper content of the upper portion of a copper vein will react with the unoxidized chalcopyrite farther down to enrich it in respect to the amount of copper it contains and convert it into bornite and chalcocite. In this way copper veins often show in the upper part, just below the oxidized zone, a body of enriched sulpliides. The veins at Butte, Montana, are notable examples of this. This enriched sulphide zone is to be observed in

Manual Of Mineralogy

general when the copper veins traverse igneous rocks. When they lie in limestones the upper portion of the vein is more liable to be characterized by the presence of the oxidized copper ores, native copper, cuprite, malachite, azurite, chrysocolla, etc. Pyrite often contains small amounts of copper and when it occurs in large bodies becomes an important ore of the metal.

Copper is produced in fifteen to twenty of the states and territories of the United States. A brief description of the chief districts in the more productive states follows. Alaska: Three districts of importance have been developed; the Ketchikan dis trict where the ores are contact bodies, and are composed chiefly of pyrrho tite, magnetite, pyrite and chalcopyrite; Prince William Sound district including several mines on Latouche Island; Copper River district where immense bodies of chalcocite and azurite occur -in limestone. Arizona: A very productive district is that of Bisbee where the ore bodies replace limestone and are closely associatea with intrusive rocks. The original ores W5Tg" chiefly cupriferous pyrite, but secondary enrichment has extended to great depths Near the surface large bodies of oxidized ores were found. The Jerome district has large bodies of ore lying in an igneous rock which through shearing has been rendered almost schistose in structure. The ores at present are largely sulphides. Morenci- Metcalf district has its ores occurring as contact deposits lying in limestone and shales into which dikes of porphyry have been in truded, and as disseminated bodies lying in the porphyry itself. The workable ores are those which have undergone secondary en richment, and consist of both carbonates and sulphides. Globe- Miami district is very productive. It has deposits that occur as lenticular replacement bodies in limestone and as deposits in fis sures in diabase. Disseminated bodies also occur. California: Important districts he in Shasta County, where the ores occur as replacement bodies along shear zones in a granite porphyry. The Plumas district is a large producer. Colorado: Most of the copper from this state comes as a by-product in the smelting of gold and silver ores and is derived chiefly from Lake, San Juan, Gilpin, Chaffee and Clear Creek counties. Idaho: Part of the output comes from the Cceur d'Alene district. The deposit consists of

Copper

disseminated bomite, chalcocite and chalcopyrite in beds of quartzite. Alder Creek district in Custer County is important. Michigan: This state was for a long period the most important producer in the country, and still ranks with the leading three. The ores are unique in that they consist wholly of native copper. They occur on Keweenaw Peninsula, the rocks of which consist of a series of alternating sandstone conglomerate beds and basic lava flows, all inclined at a steep angle to the northwest. The copper is found disseminated through and acting as a cement in the conglom erates, and in less important deposits in the amygdaloidal layers of the lavas. Montana: The one important district, and for a number of years the most important copper district in the world, is at Butte. The ores occur as replacement veins in a granitic rock. The ores have been very greatly enriched by secondary action forming at times very large sulphide bodies. The important ore minerals are chalcopyrite, chalcocite and enargite. Nevada: The important district is at Ely, where the sulphide ores occur as disseminations in highly altered porphyry. New Mexico: The Santa Rita-Hanover and the Burro Mountain districts are the chief producers. Tennessee: The chief district is that of Ducktown. The ores occur as steeply dipping lenses in a schist and contain chiefly pyrrhotite, pyrite and chalcopyrite. Utah: The Bingham district, which is a very large producer, has ores which are closely associated with a granitelike rock called monzonite which is in truded into a series of quartzites, limestones and shales. The bodies are either contact deposits in limestone or in large dissemi nated deposits in the monzonite. The Tintic district has ore bodies occurring as contact deposits, replacements in limestone and filling fissures, the last being the most important.

Important copper deposits outside of the United States are at Rio Tinto in Spain; in Australasia, at Mount Lyell in Tasmania, at Wallaroo and Moonta, South Australia, at Mount Morgan in Queensland and at different localities in New South Wales; in Mexico at Cananea and at various districts in Sonora, etc.; in Canada at the Boundary district in British Columbia and the Sudbury district in Ontario. Belgian Congo, Chile, Japan and Germany also produce notable amounts of copper.

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Copper is extensively used in the form of wire, sheet and nails. A large amount, chiefly as wire, is used as an electrical conductor. It has important uses in various alloys, as brass (copper and zinc), bronze and bell metal (copper and tin, at times zinc also), German silver (copper, zinc and nickel), etc. Copper sulphate, or blue vitriol, is used in calico printing and in galvanic cells.

Gold

Native Gold, Au, with small amounts of Ag.

Petzite, Krennerite, AuTe2.

Sylvanite, AuAgTe4. Calaverite, AuTe2.

By far the greater part of gold occurs as the native metal. It enters into only one series of compounds, the tellurides, and these minerals, while at times forming rich ore deposits, as at Cripple Creek, Colorado, are found in only a few districts. For the oc currence and associations of the gold ores see under gold, page 136 ; under calaverite, page 170; and sylvanite, page 169.

The uses of gold for jewelry, plating and coins are well known. The standard gold for United States coin is composed of 9 parts gold and 1 part copper. The gold used in jewelry is alloyed with copper and silver in order to harden it. The purity of gold is given in carats; 24 carats being the pure metal. Most of the gold used is 18 carats fine or M gold and other metals. Gold is used as the standard of international exchange and one troy ounce is worth $20.67.

Iron

Hematite, Fe203. Goethite,

Magnetite, Fe304. Limonite,

Turgite, Siderite, FeC03.

Iron, next to aluminum, is the most abundant metal in the crust of the earth. It very rarely occurs native, being found chiefly in the form of oxides, sulphides and silicates. It is found in greater or less amount in many rocks, especially in those~that~contain the kTnphiTjnTpsjyrnvpnps, micas nr flli-vm- The mineral Species tEatcontain iron are very numerous but the minerals of importance

Lead

as ores number only three or four. Iron occurs in large amounts in the sulphides, pyrite, FeS2, being the most common of all sulphides. These, however, never serve as ores of the metal because of the injurious effects of the presence of sulphur upon the iron. The minerals used as ores are the various oxides or the carbonate.

The various iron ores are formed under different conditions, and as a rule occur alone or in association with only small amounts of any one of the others. For discussion of the occurrence of the iron ores see, therefore, under hematite, page 196; magnetite, page 202; limonite, page 213; and siderite, page 224.

ffematite is by far the most important ore of iron, forming in the United States about nine-tenths of the ore produced. Li monite and magnetite form each about one-twentieth of the total, while the amount of siderite produced is almost negligible. Hema tite ore comes chiefly from the various T.ake Superior districts and to a much less extent from Alabama. Limonite is found in the Appalachian states, and magnetite in New York, New Jersey and Pennsylvania. Siderite is obtained from Ohio.

Nearly one-half of the world's production of iron ore comes from the United States; the amount producedjj&m Minnesota alone

npflrly if rnf- qnifp pinrhirrrl in n.ny -gauntry

Germany and Great Britain, Spain, France and Sweden are notable producers of iron.

The uses of iron and steel are too well known to need discussion. Copperas, or green vitriol, FeS04.7H20, is the most important salt of iron, being used in dyeing, in making inks, Prussian blue, rouge, and as a disinfectant. Rouge, Fe203, is used as a polishing powder and as a red paint. Considerable amounts of soft iron ore, known as paint ore, are ground for mineral paints, such as ocher, umber, sienna, etc.

Lead

Galena, PbS.

Cerussite, PbC03.

Phosgenite, Pyromorphite, Mimetite,

Vanadinite, Anglesite, PbS04.

Crocoite, PrCr04.

Wulfenite, PbMo04.

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Galena is the usual primary ore of lead and furnishes by far the greater part of the metal. Cerussite and anglesite are secondary minerals which occur in smaller amounts in the oxidized zone of lead deposits. Galena occurs most commonly associated with zinc ores, especially sphalerite, or in connection with silver ores. Lead, which is derived from ores that are free from silver, is known as "soft lead," while "desilverized" lead, which is obtained from silver ores, is known as "hard lead." Lead ores ™mmaniy found as replacement, deposits in limestone rocks, either in the form of beds or irregular bodies, or as small masses disseminated through a stratum of the rock. For the associations and distribution of lead ores see under galena, page 150.

Metallic lead is used in the form of sheet, pipe, etc. It is used to make weights, bullets and shot. It is a constituent of various alloys such as solder (lead and tin), type metal (lead and antimony), low-fusing alloys (lead, bismuth and tin). A large amount of lead is used in the form of the basic carbonate, which is known as white lead, and is very valuable as a paint. The oxides of lead, litharge, PbO, and minium, Pb304, are used in mak ing fine grades of glass, in glazing earthenware and as pigments. Lead chromates are used as yellow and red paints. Lead acetate, known as shear of lead, has important uses in various industries.

Manganese

Alabandite, MnS. Psilomelane, Mn02, MnO, etc.

Franklinite,

Braunite, Wad, mixture of oxides.

Manganite, Rhodochrosite, MnCOj.

Pyrolusite, Mn02. Rhodonite, MnSi03.

Manganese is an element that is widely distributed in small amounts. Traces of it at least are to be found in most rocks. It most commonly occurs in silicates, oxides and carbonates. The oxides are the most abundant, and practically all of the metal is derived from them.

The ore deposits rnamrann. illy, nrrli'angrily nf tyr-nprlgry

origin. The manganese existing in the rock-making silicates,

Manganese

through the agency of weathering processes, is changed to an oxide. By some process of concentration these minerals are often gathered together into irregular bodies lying iiysiduaLclays. At times the manganese oxides occur associated with iron oxides, and when this is the case the two are smelted together to form directly an ironmanganese alloy used in making steel. Manganese minerals also frequently occur as gangue minerals in connection with silver ores. A manganese ore to be of commercial value should contain at least 40 per cent of metallic manganese and be low in percentages of phosphorus and silica.

Manganese is obtained in the United States from the following materials: manganese ores, manganiferous iron ores, manganiferous silver ores, and from the residuum left from smelting the zinc ores of Franklin Furnace, New Jersey. Manganese ores are found in commercial deposits in Virginia, Georgia, Arkansas, Montana and California. Manganiferous iron ores are found in Virginia, and at various places in the Lake Superior iron-ore dis tricts. Manganiferous silver ores are found in the Rocky Mountain and Great Basin regions, the principal locality being Leadville, Colorado. The zinc ores of Franklin Furnace, New Jersey, con tain small percentages of manganese, chiefly in the mineral franklinite, and in the smelting of them the manganese remains in the residuum from which it is later obtained. Because of the small domestic production of manganese ores large amounts have to be imported. Important foreign deposits are in-India and RraziL the Gold Coast of West Africa, and in the Caucasus Mts., Russia.

Manganese is chiefly used in the form of alloys, those with iron being the most important. Spiegeleisen is an alloy of iron and manganese containing below 20 per cent of manganese, while ferromanganese contains manganese ranging in amount from 20 to 90 per cent. These alloys are extensively used in the manufacture of steel. They serve to take away any oxygen that might be in the iron, the oxygen uniting with the manganese and going into the slag. They serve also to introduce carbon into the steel and to prevent its oxidation, and also to counteract the bad effects of sulphur and phosphorus. Manganese has also of itself a hardening influence on steel. For these reasons manganese steels have a wide use.

Manual Of Mineralogy

Chemical uses of manganese compounds include the use of the oxide, pyrolusite, Mn02, as an oxidizer in the manufacture of chlo rine, bromine and oxygen, as a drier in paints and varnishes, as a decolorizer of glass, and in the dry-cell battery. Potassium per manganate is used as a disinfectant . Manganese is used in print ing calico and for coloring bricks, pottery and glass.

Mercury

Cinnabar, HgS.

Mercury, or quicksilver, is neither abundant nor widespread in its occurrence. The native metal is sometimes found and other rare minerals of mercury are occasionally noted, but practically the only ore of the metal is the sulphide, cinnabar. For the occurrence and distribution of mercury, therefore, see under cinnabar, page

The most important use of mercury is in the amalgamation process for recovering gold and silver from their ores. It is used in the form of an amalgam with tin in "silvering" mirrors. It is used in thermometers, barometers, etc. Mercury salts, especially calomel, are used in medicine. The sulphide is used as the pig ment called vermilion.

Molybdenum

Molybdenite, MoS2. Wulfenite, PbMoCh.

Molybdenum is a rare element occurring chiefly as the sulpiride, molybdenite. More rarely wulfenite may serve as an ore. See under molybdenite, page 148, and under wulfenite, page 325, for their occurrence and distribution. Only a small amount of molyb denum is produced in the United States.

Molybdenum is used to a small extent as a steel-hardening metal. In the form of ammonium molybdate it is used as a chemical reagent, as a fireproofing material, and asm, disinfectant. Molyb denum compounds are also used to colonieather and rubber.

Platinum

Nickel

Pentlandite, Chloanthite, NiAs2.

Millerite, NiS. Gersdorflite, NiAsS.

Niccolite, NiAs. Genthite, Ni2Mg2Si3Oio.6lI20(?).

Nickeliferous Pyrrhotite. Garnierite, noumeaite, H2NiSi04(?). Linnaeite,

Nickel is a comparatively rare element, found oiten associated with cobalt. Its minerals are frequently found in small amounts in connection with magnesian jgpoons rnr.k-s- where it is commonly psanniated with chromite. Only a few localities produce the metal in commercial quantities, the world's output coming mostly from the nickeliferous pyrrhotite ores of Sudbury, Ontario, Canada, or from the silicate (garnierite) ores of New Caledonia. The pro duction of nickel from ores mined in the United States is very small.

The chief use of nickel is in various alloys. Nickel steel, con taining about 3.5 per cent of nickel, has a wide use because of its great strength and toughness. Other alloys are German silver (nickel, zinc and copper); metal for coinage (nickel and copper). Large amounts of nickel are used in nickel plating.

Platinum

Native Platinum, Pt, with some iron and traces of the rare platinum metals. Sperrylite, PtAs2.

Platinum is a rare element which usually occurs native. Its only known compound occurring as a mineral is the arsenide, sperrylite, which has been found very sparingly in two or three localities in association with copper and nickel ores. Platinum is characteristically found associated with the magnesian rocks called peridotites and often with chromite. The only commercial deposits of platinum so far known are placer deposits, the materials of which have been derived from the weathering of the rocks that contained the platinum is disseminated particles. For the occur rence and distribution of platinum see page 142.

The uses of platinum chiefly depend upon its high fusing point (1700° to 1800° C.) and its resistance to chemical reagents. It

Manual Of Mineralogy

is valuable for all sorts of laboratory apparatus, such as crucibles, dishes, spoons, etc. It is used in the sulphuric acid industry for concentrating kettles and also in the contact process for the manu facture of the acid in the form of finely divided platinum, in con tact with which the acid is formed. It is largely used as wire to form the electrical connections with the filaments of incandescent electric lights. It is used in jewelry, particularly as the setting for diamonds, in dentistry in the making of false teeth, in electrical heating apparatus, for sparking plugs in explosion motors, in the measuring of high temperatures, in electrical contacts, etc. Potas sium chloro-platinate, 2KCl.PtCl2, is employed in photography.

Silver

Native Silver, Ag. Argentite,

Stromeyerite, .\g2S.Cu2S. Sylvanite, AgAuTe4. Pyrargyrite, 3Ag2S.Sb2S3.

Proustite, 3Ag2S.As2S3. Stephanite, 5Ag2S.Sb2S3. Polybasite, 9Ag2S.Sb2S3.

Cerargyrite, AgCl. Embolite,

It is to be noted that none of the silver minerals contains oxygen, the most important series being included in the sulphide and sulpho-salt groups. Besides the distinctively silver minerals listed above, several minerals of other metals contain at times sufficient silver to make them valuable ores of the metal. Most important among these are the argentiferous varieties of galena, chalcocite, bornite, chalcopyrite and tetrahedrite. These minerals form the most common ores of silver, either because of the small amounts of silver which they contain, or the small amounts of silver minerals associated with them.

The important ores of silver can be divided into three main classes, namely, the siliceous ores, copper ores and lead ores. The siliceous ores are those ores which contain large proportions of quartz with small amounts of gold and silver minerals and are comparatively free from other metals. Most of them contain both gold and silver, the gold value being often in excess of the silver value. The chief districts in which this type of silver ore is pro-

Silver

duced are Tonopah in Nevada; the San Juan, Leadville and Aspen districts in Colorado; Granite, Silmrhow counties in Montana; and in various districts in Idaho, Arizona, California, South Dakota and Utah. The important deposits of copper ores which contain a notable amount of silver are found at Butte in Montana; at the Bingham and Tin tic districts in Utah; at the Bisbee, United Verde and Silver Bell districts in Arizona; in Shasta County, California; and at various places in Idaho, Michigan and Colorado. The important deposits of lead ore that produce silver are to be found at the Coeur d'Alene district in Idaho; at the Bing ham and Tintic districts in Utah; at the Creede, San Juan and Lead ville districts in Colorado; and at various districts in Nevada, Montana and Arizona.

Thfi important, foreign couptrips for th° nf gUiror-aro

UuNtrc) nnr] AnatmUo In Mexico the chief districts are

Guanajuato, Pachuca, El Oro, Parral and Santa Eulalia; in Canada in the Boundary and Kootenai districts in British Columbia and the Cobalt district in Ontario ; in Australia chiefly from the Broken Hill district in New South Wales.

In connection with silver ores the following facts are of interest. Owing to the high value of silver, only a small percentage of the metal in an ore is sufficient to make it valuable. For instance, an ore that contained only 0.34 per cent of silver would yield 100 ounces to the ton, which is an amount much larger than usual. In giving the assay value of an ore, the amount of silver is usually stated in ounces per ton of ore. Lead-silver ores are of value be cause in the smelting the silver will be taken up by the lead. Ores containing calcium carbonate and iron and manganese minerals are of value because of the service of these materials in fluxing the ore. Zinc minerals detract from the value of an ore because of the added difficulty in smelting caused by their presence.

The uses of silver for coinage, for various useful and ornamental objects and for plating are too well known to need discussion. The standard silver coin for the United States contains nine parts of silver to one of copper. Silver salts are used in photography and caustic silver (AgN03) is employed in medicine.

Manual Of Mineralogy

Tin

Staimite, Cu2S.FeS.SnS. Cassiterite, Sn02.

The only ore of tin of importance is the oxide, cassiterite. This is a mineral which, while occurring in small quantities in many localities, is found only in a comparatively few commercial de posits. For the occurrence and distribution of the mineral see page 206. The United States at present produces only a small amount of tin ore.

Tin is chiefly used in the coating or "tinning" of metals, es pecially iron. The tin plate thus formed is used in roofing, in various utensils, etc. _An amalgam of tin and mercury is used in "silvering" mirrors. Various alloys are valuable, such as solder (tin and lead), bronze and bell metal (copper and tin). The artificial oxide of tin is used as a polishing powder. Stannic chloride is employed as a mordant in dyeing.

Titanium

Ilmenite, titanic iron, FeTi03 Octahedrite, Ti02.

with MgTiOa and Fe203. Brookite, Ti02.

Rutile, Ti02. Titanite, CaTiSiCh.

Titanium is a rare element, but is quite widely distributed in small quantities. In the form of the minerals rutile and titanite it is present in most igneous rocks. Ilmenite is commonly found in the basic igneous rocks, and is often associated with magnetic iron ores.

Very little titanium ore is produced in the United States. Rutile deposits occur in Virginia, and some of the Adirondack magnetite deposits contain considerable ilmenite.

The present uses of titanium are rather limited. It has been used in steel and cast iron, in which it serves to eliminate the oxygen and nitrogen. It is also said to give a high tensile strength and great ductility to the steel. It is being used to some extent in the manufacture of electrodes for arc lights. The oxide is used to give a yellow color to porcelain, and to give a natural color to false teeth.

Vanadium

Tungsten

Wolframite, Scheelite, CaW04.

Hiibnerite, MnW04.

Tungsten is a rare acid-forming heavy metal found chiefly in the tungstates of iron and calcium, wolframite and scheelite. For the occurrence and distribution of these minerals see under wolframite, page 323, and scheelite, page 324.

The most important use to which tungsten is put is as a steel hardening metal. Tungsten steels hold their temper at high temperatures and are therefore valuable for the making of high speed tools, etc. Because of its high fusing point metallic tungsten is used as a filament in incandescent electric lights. Sodium tungstate is used in fireproofing cloth and as a mordant in dyeing. Calcium tungstate is used as the luminous screen in X-ray ap paratus.

Vanadium

Roscoelite,

Vanadinite, Carnotite,

Vanadium is an acid-forming metal which is known in a number of very rare minerals. The three listed above are the only ones which occur in sufficient quantities in the United States to be available for ores. Roscoelite is a green micaceous mineral con taining about 2 per cent of metallic vanadium. It is found in a soft sandstone near Placerville, Col. Carnotite is a sulphuryellow pulverulent mineral of doubtful composition which is found in sandstones in several districts in Colorado and Utah, near the boundary line between the two states. Vanadinite is a secondary lead mineral which is found sparingly in the oxidized zones of certain lead deposits in Arizona and New Mexico. All of these ores are low grade, and are worked only in a small way and at intervals. The chief supply of vanadium ores at present comes from Peru, where there are large deposits of an impure carbonaceous sulphide of vanadium, known as patronite.

Vanadium is used chiefly in steel, and is said to give it great

Manual Of Mineralogy

tensile and elastic strength. Metavanadic acid, HV03, is used as a yellow pigment, known as vanadium bronze. Vanadium oxide serves as a mordant in dyeing.

Zinc

Sphalerite, ZnS. Smithsonite, ZnC03

Zincite, ZnO. Willemite, Zn2Si04.

Franklinite,

Calamine,

The sulphide, sphalerite is t.lia ore 0f

zinc. The carbonate, smithsonite, and the silicate, calamine, are usually associated with sphalerite deposits as secondary min erals. The three minerals, zincite, franklinite and willemite, are found in unique deposits at Franklin Furnace, New Jersey. To gether with a large number of rare and unusual minerals they form anticlinal beds lying intercalated in a limestone series. In general sphalerite, the chief ore of zinc, is found in irregular replacement deposits in limestone. It is very frequently intimately associated with lead minerals. For its occurrence and distribution see page

Metallic zinc, or spelter, as it is called, is chiefly used for gal vanizing iron, as an alloy with copper in brass, and in storage and telegraph batteries. Zinc dust or zinc shavings are used to pre cipitate gold from its solution in the cyanide process. Large amounts of zinc oxide, or zinc white, are used as a. white paint which is even more permanent than lead paints- Zinc chloride is used as a wood- preservative.

Occurrence And Association Of Minerals

Although minerals are found in many modes of occurrence, and in an almost endless variety of associations, there are, however, certain frequent and important ways in which they occur that should be pointed out. An understanding of the conditions under which a particular mineral is usually formed, together with a knowledge of what other minerals are characteristically associated

Rocks And Rock-Making Minerals 345

with it, is of the greatest value. On the following pages is given, therefore, a brief discussion of the more important modes of min eral occurrence, and of the more common associations observed.

Rocks and Rock-making Minerals

Since by far the greater part of minerals occur as rock constit uents a short description of the more important rock types and of the common rock-making minerals will be given first. Only the barest outline of the subject can be given here and for more de tailed information the reader is referred to one of the textbooks which treat more particularly of petrology.

Rocks may be divided into three main divisions, namely:

I. Igneous.

II. Sedimentary.

III. Metamorphic.

I. Igneous Rocks

Igneous Rocks, as the name indicates, are those which have been formed by the cooling and consequent solidification of a once hot and fluid mass of rock material. This liquid mass is known as a rock magma. Ajnagma, in a measure, is like a solution containing in a dissociated condition the elements which, when the mass cools sufficiently, unite to form the various minerals that go to make up the resulting rock. The elements which form the chief constituents of the magmas of igneous rocks are oxygen, silicon, aluminum, iron, calcium, magnesium, sodium and potassium,

named in the nf their ahiindancp. When a magma cools these elements unite to form various mineral molecules, which, when the point of supersaturation is reached, crystallize out to form the minerals of the rock. Certain compounds under similar conditions crystallize out of the fluid mass earlier than do others. In most igneous rocks a more or less definite order of crystallization for their mineral constituents can be determined. In general the more basic minerals or those which contain the smaller amounts of

Manual Of Mineralogy

silica,, which is the acid element in igneous rocks, are observed to crystallize first and the more acid minerals last. Among the commoner rock-making minerals the following would be the usual ( order of crystallization; iron oxides like magnetite first, then the y ferro-magnesian minerals like pyroxene, next the plagioclase feld spars, then orthoclase and lastly quartz.

The type of minerals to be found in any igneous rock would / depend chiefly upon the chemical composition of the original V magma. If the magma was acid in character, i.e., had a high J percentage of silica, the resulting rock would contain the more acid / minerals and an abundance of free quartz. It would usually be 1 light in color. If, on the other hand, the magma had a low per centage of silica, or in other words was basic in character, the result ing rock would contain the more basic minerals and would not show free quartz. It would also in general be dark in color.

In addition to the wide variation in chemical and mineral com position shown by igneous rocks there is also a variation in thenphysical structure. This is dependent upon the mode of origin of the rock. If a rock has been formed from a magma buried at a considerable depth in the crust of the earth it must have cooled very slowly and taken a long period of time for its gradual crystalli zation and solidification. Under these conditions the mineral particles have had the opportunity, because of the slowness of crystallization, to grow to considerable size. A_Jock having ouch a deep-seated origin has, therefore, n mars-grained structure the various minerals that go to form the rock can in wnpral he

differentiated and recognized by the unaided eve. Such rocks are

commonly termed plutonic.

On the other hand, if, by volcanic forces, the magma has been extruded upon the surface of the earth or intruded in the form of dikes into the rocks lying close to the surface, its subsequent cooling and solidification go on quite rapidly. Under these conditions the mineral particles have little chance to grow to any size and the resulting rock is fine-grained in character. In some cases, indeed, the cooling has been too rapid to allow the separation of any min erals and the resulting rock is like a glass. Ordinarily the mineral constituents of such a rock are only to be definitely recognized by a

Plutonic, Coarse-Grained Rocks

microscopic examination of a thin section of the rock. Such igne ous rocks are known ns volcanic, rocks.

An igneous met- hppniKP nf flip merle of its, formation -af parti'nW hjIUpK m-yy hp -an jd to interlock with rit.W In other words, it Ls a solid mass, and each mineral pw-lo fa intimately and firmly embedded in the surrounding particles. This structure will enable one ordinarily to distinguish an igneous from a sedimentary rock, the latter being composed of grains which do not interlock with each other but stand out, more or less, by them selves. A sedimentary rock is not, so firm and coherent as an igne ous rock. Further the texture of an igneous rock is the same in all directions and it forms a fairly uniform and homogeneous mass. This characteristic will enable one to distinguish an igneous frnna a metamorphic rock, since the latter shows a more or less definite parallel arrangement nf its minerals and a banded structure.

Because of the almost infinite variation possible in the chemical composition of their magmas, and because of the various condi tions under which they may form, igneous rocks show likewise a wide variation in character. The more common and important types, however, are very briefly described below.

Plutonic, Coarse-grained Rocks

1. Granite. A granite is a medium- to coarse-grained, lightaolnred rock having an even texture and consisting chiefly of quartz and a feldspar. Frequently both orthoclase and a plagioclase feldspar, and usually also small amounts of mica or hornblende are present. The feldspars can be recognized by their color and cleav age. Frequently the orthoclase is colored flesh-color or red, while the soda-lime feldspar is usually white. The quartz is recognized by its glassy luster and conchoidal fracture. It is usually white or smoky-gray in color and is found in irregular grains filling up the interstices between the other minerals. The mica, which may be either muscovite or biotite, is to be recognized by its cleavage. Granite is a common rock type.

2. Syenite. A syenite is a medium- to coarse-grained lightcolored rock with an even texture and much like a granite in ap-

Manual Of Mineralogy

pearance. It is to be distinguished from granite, however, by the fact that it contains little or no quartz. Its chief minerals are the feldspars, with more or less hornblende, mica or pyroxene. A variety, known as nephelite-syenite, is characterized by the presence of considerable amounts of nephelite. Another vari ety, called anorthosite, is composed chiefly of labradorite. The feldspars, mica and hornblende, may be distinguished as described under granite. The pyroxene resembles hornblende in appearance, but does not show as good a prismatic cleavage. Nephelite is recognized by its lack of a distinct cleavage and its oily and greasy luster. Syenites are not very common.

3. Diorite. Diorite is a medium- to coarse-grained dark gray or greenish colored rock having an even texture and consisting chiefly of hornblende and a feldspar, in which the hornblende predominates. Often fine grains nf imn rn-o my observed, and frequently considerable amounts of biotite. It is a common rock type.

4. Gabbro. Gabbro is a medium- to coarse-grained dark gray

to greenish black rock with an even texture composed chiefly of pyroxene and a feldspar. It is closely similar to diorite. the distinction lying in the fact that it contains pyroxene instead of SirrpbiboJji these two minerals, as they occur in these rocks, cannot always be told apart by a megascopic examination. The pyroxeng is usually in small crystal grains with rather poor pris matic cleavages which are at nearly right angles to each other. Hornblende is more liable to be in longer prismatic crystals and shows hector the angle of which is about 125°. It is a

common rock.

5. Dolerite. This is a name given to those varieties of diorite and gabbro which are too fine-grained in character to enable one to tell megascopically whether the dark-colored mineral which they contain is hornblende or pyroxene.

6. Peridntite. A peridotite is a medium- to coarse-grained dark green to black rock with an even texture which consists \yl~inlly nf ferromagnesian minerals. These are chiefly olivine, pyroxene and hornblende. As one or the other of these minerals predominates, various variety names are used, such as dunite for

Volcanic, Fine-Grained Igneous Rocks 349

an olivine rock and pyroxenite and homblendite for respectively pyroxene and hornblende rocks. Common accessory minprala found in these rocks are ilmenit,er chromite and garnet. The peridotites are not very common in their occurrence.

Volcanic, Fine-grained Igneous Rocks

Because of their very fine-grained structure volcanic rocks cannot in general be readily told apart. A number of different types are recognized, the distinction between them being based, however, chiefly upon microscopic study. In the field only an approximate classification, depending upon whether the rock is light or dark in color, can be made. A brief description of these two types of volcanic rocks follows.

1. Felsite. This is a dense fine-grained rock type with a stony texture and includes all colors except dark gray, dark green or black. These rocks may, by the aid of a lens, still show a very fine-grained structure or their mineral constituents may occur in such small particles as to give them a dense and homogeneous, often a flinty, appearance. By microscopic study the felsites have been divided into the following groups; rhyolite, consisting chiefly of alkaline feldspars and quartz; dacite, lime-soda feldspars and quartz; trachyte , alkaline feldspars with little or no quartz; andesite, soda-lime feldspars with little or no quartz; phanolite, alkaline feldspars and nephelite. As a rule these varieties are not to be distinguished from each other in the field. The felsites are widespread in their occurrence, being found as dikes and sheets intruded into the upper part of the earth's crust or as lava flows which have been poured out upon the earth's surface.

2. Basalt. The basalts are dense fine-grained rocks that a j-p of very dark color, green or black. They are composed of microscopic grains of a soda-lime fddsnar with nvrnxene. iron ore, often more or less olivine and at times biotite or hornblende. These rocks are formed under the same conditions as the felsites and are to be found occurring in the same ways.

3. Glassy Rocks. Some of the volcanic rocks have cooled so rapidly that they are wholly or in part made up of a glassy material

Manual Of Mineralogy

in which the different elements have not had the necessary op portunity to group themselves into definite minerals. If the entire rock is composed of glass it is called obsidian, when it has a bright and vitreous luster; pitchstone when its luster is dull and pitchy; perlite if it is made up of small spheroids; and pumice if it has a distinctly cellular structure. These rocks may also have distinct crystals of various minerals embedded in the glass, in which case they are known as glass porphyries (see below for a definition of a porphyry) or vitrophyres.

Porphyries. Igneous rocks at times show distinct crystals of certain minerals which lie embedded in a much finer-grained material. These larger crystals are known as phenocrysts, and the finer-grained material as the groundmass of the rock. Rocks exhibiting such a structure are known as pornhvries. The pheno crysts may vary in size from crystals an inch or more across down to quite small individuals. The groundmass may also be composed of fairly coarse-grained material or its grains may be microscopic in size. It is the distinct difference in size existing between the phenocrysts and the particles of the groundmass that is the distinguishing feature of a porphyry. This peculiar structure is due to certain conditions prevailing during the formation of the rock which permitted some crystals to grow to considerable size before the main mass of the rock consolidated into a finer- and uniform-grained material. The explanation of the reasons why a certain rock should assume a porphyritic structure would involve a more detailed discussion than it is expedient to give in this place. Any one of the above described types of igneous rocks may have a porphyritic variety, such as granite-porphyry, diorite-porphyry, felsite-porphyry, etc. Porphyritic varieties are more lihlo tn necnr in connection with volcanic rocks, and they grp aJsn frequently in the case of the more acidjypes.

II. Sedimentary Rocks

Sedimentary rocks a.re secondary in their origin, the materials of which they are composed having been derived from the decay and disintegration of some previously existing rock mass. They

Sedimentary Rocks

have been formed by a deposition of sediments in a body of water. They may be divided into two classes, depending upon whether their origin has been mechanical or chemical in its nature. In the case of the sedimentary rocks of a mechanical origin, their constitu ent particles have been derived from the disintegration of some rock mass, and have been transported by streams into a large body of quiet water, where they have been deposited in practically horizontal layers. Sedimentary rocks of chemical origin have had the materials of which they are composed dissolved by waters circulating through the rocks and brought ultimately by these waters into a sea, where through some chemical change they are precipitated upon its floor, also in horizontal layers. These hori zontal beds of sediments are ultimately consolidated into the masses known as sedimentary rocks.

Sedimentary rocks are therefore characterized by a parallel arrangement of their constituent particles into layers and beds which are to 'be distinguished from each other byTHiTerences in thickness, size of grain and often in color. It is to be noted, further, that sedimentary rocks in general are composed of an aggregate of individual mineral particles, each of which stands out in a way by itself and does not have that intimate interlocking relation with the surrounding particles which is to be seen in the minerals of an igneous rock. In all the coarser-grained sedimenlary-ranks-there is some material which, noting as a. cement, surrounds the individual mineral particles and binds them together. This cement is usu ally either silica, calcium ca..te nr iron ovule l'hn chiefminerals to~be found in sedimentary rocks are quartz Find -car bonate, calcite or dolomite— These give rise to the twochief of sedimentary rocks, the sandstones and the limestones. A brief description of these rocks follows.

1. Sandstone. Sandstones are mechanical in their origin, being formed by the consolidation into rock masses of beds of sand and gravel. Usually the constituent grains are rounded and water-worn, but at times they may be more or less angular in shape. With the variation in the size of the mineral particles the rocks themselves vary in their grain. Coarse-grained sandstones formed from gravels are known as conglomerates. The cement

Manual Of Mineralogy

which serves to bind the sand grains together may be deposited silica, a carbonate, usually calcite, an iron oxide, hematite or limonite, or fine-grained argillaceous or claylike material. The color of the rock will depend in large measure upon the character of the cement. The rocks which have silica or calcite as their binding material are light in color, usually pale yellow, buff, white to gray, while those that contain an iron oxide are red to reddish brown. It is to be noted that when a sandstone breaks it is usually the cement that is fractured, while the individual grains remain un broken, so that the fresh surfaces of the rock have a granular ap pearance and feeling. The chief mineral of sandstones is quartz, but at times a rock may contain notable amounts of feldspar and is then termed an arkose. Graywacke is a sandstone, usually of a gray color, which in addition to quartz and feldspar contains par ticles of other rocks and minerals.

2. Shale. The shales are very fine-grained sedimentary rocks which have been formed by the consolidation of beds of mud, clay or silt. They have usually a thinly laminated structure. Their color is commonly some tone of gray, although they may be white, yellow, brown, green to black. They are composed chiefly of kaolin, mica, etc., but are too fine-grained to permit the recognition of their mineral constituents by the eye alone. By the introduction of quartz and an increase in the size of grain they grade into the sandstones.

3. Limestone. The limestones are carbonate rocks composed usually chiefly of calcite, although dolomite may also be at times an important constituent. The carbonate has in the great major ity of cases been extracted from the sea water by the agency of minute organisms and then deposited in beds which ultimately are consolidated into rock. These rocks are usually fine- and even grained in structure and sometimes quite dense. Some limestones are quite pure calcite, while others contain claylike materials and various oxides as impurities. The color of a limestone is usually gray, although it may be white, yellow, brown to almost black. It is a soft rock, to be easily scratched by a knife. It will effervesce readily in any common acid. In the case of limestones composed of dolomite, however, the acid needs to be heated. Oolite, or oolitic

Metamorphic Rocks

limestone, is a variety which consists of an aggregate of small spherical concretions. Chalk is a very fine-grained friable lime stone composed of shells of minute sea animals known as foraminifera. Travertine is a deposit of calcium carbonate formed hv springs. A fine example exists in the deposits formed by the Mam moth Hot Springs, Yellowstone Park. Marl is a loose, earthy material composed of a carbonate mixed with clay in variable amount.

III. Metamorphic Rocks

Metamorphic rocks are rocks which have undergone some chemical or physical change subsequent to their original formation. This change has been brought about by means of high temperature and pressure aided by the action of water and other chemical agents. The changes involve the formation of new minerals, the adding or subtracting of chemical constituents and a physical readjustment of the mineral particles to conform to the existing pressure. The original rock from which a metamorphic rock has been derived may be either igneous or sedimentary. As these rocks become involved in movements of the earth's crust, they are subjected to extreme pressures accompanied usually by high tem peratures. The result will be frequently to transform the existing minerals into others more stable under the new conditions. The physical structure of the rock will also ordinarily be changed during the process. Because of the pressure to which the rock is subjected the mineral particles will be more or less broken and flattened and rearranged in parallel layers. This banded or laminated character given by the parallel arrangement of its minerals is themost strik ing peculiarity of a metamorphic rock. Because of this Structure'S" metamorphic rock can be distinguished from an igneous rock. Further, in the great majority of cases a metamnrplde mel- has a crystalline, .structure distinguishes it from a sedimentary rock. There are, of course, all gradations from a typical metamorphic rock into an unaltered sedimentary rock on the one hand and into an unaltered igneous rock on the other. The most com mon types of metamorphic rocks are briefly described beyond.

Manual Of Mineralogy

1. Gneiss. When the word gneiss is used alone it usually refers to a metamorphic rock composed essentially °f quartz, feldspar and a. mioa. The quartz and feldspar occur together in layers which are separated from each other by thin drawn-out bands of mica. A gneiss has usually a light color, although this is not necessarily so. Various varieties of gneiss have received distinctive names, most of which are self-explanatory, like bandedgneiss, lenticular-gneiss, biotite-gneiss, hornblende-gneiss, granitegneiss, diorite-gneiss, etc. Gneiss is a very common rock type, especially in regions in which the oldest rocks, those of the Archaean age, are found. Gneisses have been more mmmnnly derived by the metamorphism of igneous rocks, mostly granites, but may have been formed from sedimentary rocks as well.

2. Mica-schist. Mica-schist is a rock composed essentially of quartz and a mica, usually either muscovite or biotite. The mica is the prominent mineral, occurring in irregular leaves and in foliated masses. The mica plates all lie with their cleavage planes parallel to -each other and give to the rock a striking lam inated or "schistose" structure. The mica-schists frequently carry characteristic accessory minerals, such a/'gametfaurolite)

<Ccvanita> <piclote£omblen(?ebetc. They may have been derived from either an igneous or a sedimentary rock. Next to the gneis ses, they are the most common metamorphic rocks.

3. Quartzite. As its name indicates, a quartzite is a rock composed essentially of quartz. It is a firm, compact rock which breaks with an uneven, splintery or conchoidal fracture. It is usually light in color. Quartzite has been derived from a sandstone by intense metamorphism. It is a common and widely distributed rock.

4. Slate. Slates are exceedingly fine-grained rocks which have a remarkable cleavage which permits them to be split into thin and broad sheets. Their color is commonly gray to black, but may be green, yellow, brown, red, etc. They have been formed commonly by the metamorphism of shales. Their characteristic slaty cleav age may or may not be parallel to the bedding planes of the original shales. They are quite common in occurrence.

Common Rock-Making Minerals

5. Various Schists. There are various other kinds of schistose rocks, which are chiefly derived by the metamorphism of the ferromagnesian igneous rocks. The most important types are

rfalcschist) amphibolite or hornblende-schist. They

each are characterized, as their names indicate, by the preponder ance of some metamorphic ferromagnesian mineral.

6. Marble. A marble is a metamorphosed limestone. It is a crystalline rock composed of grains of calcite, or more rarely dolomite. At times the individual grains are so small that they cannot be distinguished by the eye, and again they may be quite coarse and show clearly the characteristic cleavage of the mineral. Like limestone, a marble is characterized by its softness and its effervescence with acids. When pure, marble is white in color, but it may show a wide range of color, due to various impurities that it contains. It is a rock which is found in many localities and at times in thick and extensive beds.

The Common Rock-making Minerals

Although many minerals are found as rock constituents, those which can be termed common and characteristic rock-making minerals are comparatively few in number. The following list gives the names of these minerals, with a brief statement in each case of the types of rocks in which they most commonly occur.

1. Quartz. Quartz, Si02, is a very common and widely dis tributed rock-making mineral. It is found in all the -colored. acid, igneous and metamorphic rocks. It is the chief constituent of sandstones and quartzites. It is to be recognized by its hard ness (7), its vitreous luster, lack of cleavage and conchoidal fracture. When it occurs in igneous rocks it often has a gray or smoky color.

2. The Feldspars. The feldspars include orthoclase and microcline, KAlSi308, albite, NaAlSLOs, anorthite, CaAl2Si208, and various mixtures of these last two as oligoclase (3 albite to 1 anorthite), andesine (1 albite to 1 anorthite) and labradorite (1 albite to 3 anorthite). They are very common rock-making minerals and are found in a great variety of rock types. They

Manual Of Mineralogy

are characteristic of most igneous rocks, and frequently constitute a large proportion of them. They are found in the gneisses and to a less extent in some sandstones. They are to be distinguished by their two cleavages at right angles or nearly so, their vitreous luster and their hardness (6). It frequently is difficult, if not impossible, to tell the kind of feldspar present in a rock by inspection alone. Under favorable conditions twinning striations may be observed on the best cleavage face, which would indicate that the feldspar belonged to the plagioclase group (see page 238) and could not be orthoclase.

3. Nephelite. Nephelite is a silicate whose composition is essentially NaAlSi04. It is restricted in its occurrence, being found only in certain igneous rocks, such as the nephelite sye nites, which are low in percentages of silica. It is often mistaken for quartz, but the two minerals are practically never found to gether. It is best determined by a chemical test. Unlike most rock-making minerals, it is readily soluble in hydrochloric acid and the solution gelatinizes on evaporation.

4. Sodalite. Sodalite, is similar in its occurrence to nephelite, with which it is commonly associated. It may be greenish gray or white in color, but is usually blue. Haiiynite and noselite are similar but rare species which occur in the same way.

5. Leucite. Leucite has the composition It is a rare rock-making mineral found chiefly in rather basic lavas. It is commonly in the form of phenocrysts which show trapezohedral forms. It is white to gray in color with a dull vitreous luster.

6. The Micas. The micas are common rock-making minerals. They may be divided into two classes: the light colored micas which are chiefly muscovite, and the dark colored micas consisting mostly of biotite. They are to be determined by their micaceous structure, eminent cleavage and the elasticity of their leaves. Muscovite is found in granites and syenites and other igneous rocks. It is especially common in the metamorphic rocks, partic ularly the gneisses and schists. Biotite is found in many igneous rocks such as the granites, syenites and felsites. It occurs also in the gneisses and schists.

Common Rock-Making Minerals

7. The Pyroxenes. The pyroxenes form an important series of rock-making minerals which, although the different members vary considerably in composition, are closely related crystallographieally. The important types are hypersthene, diopside, common pyroxene, augite, with as well, and segirite, The pyroxenes are characteristically found in igneous rocks, particularly those that contain large amounts of lime, iron and magnesia, such as basalt, gabbro, peridotite, etc. Diopside and common pyroxene are at times found in metamorphic limestones. The pyroxenes vary in color from white through green to black. They occur usually in small grains or in short prisms. If they show distinct crystal outlines, they can be told by the square cross section of their prisms. They have a rather poor cleavage.

8. The Amphiboles. The amphiboles or hornblendes are calcium, magnesium, iron metasilicates which closely resemble the pyroxenes in their chemical composition. The most important members of the group are tremolite, actinolite, common hornblende, with a molecule containing aluminum and ferric iron besides, and arfvedsonite, which contains chiefly soda, lime and iron protoxide. The amphiboles are particularly characteristic of the metamorphic rocks, but are found in the igneous rocks as well. Tremolite is most commonly found in crystalline metamorphosed limestones, actinolite in schists, hornblende in granites, syenites and diorites, and also in gneisses and hornblende schists. The amphiboles commonly occur in bladed prismatic crystals with a good prismatic cleavage. The cleavage angle is broad, having a value of about 125°. They vary in color from white through green to black, but are most commonly green.

9. Chrysolite, or Olivine. Chrysolite, or as it is more commonly termed when spoken of as a rock constituent, is an orthosilicate of magnesium and ferrous iron It is a characteristic constituent of the ferromagnesian igneous rocks such as gabbros, peridotites and basalts. It is almost the only mineral present in the igneous rock known as dunite. It is

Manual Of Mineralogy

usually green in color, with a vitreous luster and granular struc ture.

10. Kaolin. Kaolin is a silicate of aluminum, EUAljSiiO*, which is always secondary in its origin. It is formed by the weath ering of some aluminum silicate, usually a feldspar. It may occur in quite pure masses where feldspathic rocks have been entirely altered, but is most commonly found, however, in an impure state in clay, and in the rocks formed from claylike mate rials such as shales, slates, etc. When pure it is often friable or mealy in structure, although at times it is compact. It varies in color from white to yellow, brown, red, etc., depending upon the amount and character of the foreign material mixed with it

11. Chlorites. The chlorites are a group of green-colored micaceous minerals of which clinochlore is the most common member. In composition they are hydrous silicates of aluminum and magnesium. They are always secondary in their origin. They are frequently formed by the alteration of the ferromngnesinn minerals occurring in igneous rocks. The green color of such rocks is usually due to the presence of chlorite. They are also common in the chlorite-schists, in green slates, etc. They are to be recognized

12. Serpentine. Serpentine, HJVIgaSiaOg, is also a secondary mineral formed by the alteration of some original ferromagnesian mineral, such as pyroxene, amphibole, and especially olivine. It QmuvJbenioixv.m -aiterecHgneous rocks and in metamorphic fokffr It may occur in disseminated particles or in rock masses, of which it is the chief mineral. It is usually of some shade of green in color and has an oily or waxy luster. It is usually mas sive in structure, but may become coarsely fibrous in the variety known as chrysotile.

13. Talc. Talc, is similar in its origin and oc currence to serpentine. It is found at times in altered igneous rocks, but is more characteristic of mctamornhic rocks where it may occur in large beds as soapstone. It is characterized by its extreme softness (1), greasy feel and also frequently by its foliated structure.

Accessory Rock-Making Minerals 359

14. Calcite. Calcite, CaC03, is a common and widely dis tributed rock-making mineral found chiefly in the sedimentary and metamorphic, jacks. Such rocks as the limestones, marbles and chalks are composed almost entirely of the mineral. It is to be told by its softness (3), its rhombohedral cleavage and its ready effervescence in cold acids.

15. Dolomite. Dolomite, is found in the same way as calcite but less commonly. The two minerals are usually associated with each other and form dolomite marbles and dolomitic limestones. Its physical properties are practically the same as those of calcite. It will only effervesce, however, in hot acids.

Accessory Rock-making Minerals

In addition to the more important and common rock-making minerals that have been described in the preceding pages, there is a group of minerals which are characteristically found as rock con stituents but in a minor way. They occur usually only as small and scattered crystals in the rock and seldom become one of its prime constituents. These minerals are known as accessory rock making minerals. The occurrences of the more important of them are briefly described below.

1. Garnet. Garnet, is a common accessory mineral, being par ticularly characteristic of the metamorphic rocks. It is found frequently in micarschists, hornblende-schists, gneisses and meta morphosed limestones. More rarely it is found in igneous rocks. It occurs in small irregular grains or frequently in fair-sized definitely shaped crystals. It is usually red or brown in color. For the different varieties of garnets and their distinguishing fea tures, see p. 259.

2. Epidote. Epidote is formed by the alteration of silicates containing lime, iron and aluminum. It is also characteristic of metamorphosed limestones. It may be associated with chlorite, calcite, etc. It is usually found in bladed crystalline masses and has a characteristic yellow-green color, is hard and has one good cleavage.

3. Staurolite. Staurolite is found in metamorphic rocks, such as the micarschists and slates. Sometimes it is a constituent of

Manual Of Mineralogy

gneiss. It is associated with mica, quartz, garnet, cyanite, etc.

It is characterized by a brown color, hardness (7) and prismatic orthorhombic crystals which may show cross-shaped twins.

4. Cyanite. Cyanite, Al2Si05, is a rather rare accessory min eral which is found in gneisses and mica-schists. It is associated with muscovite, quartz, garnet, staurolite, etc. It is to be distinguished by its bladed structure, one good cleavage, blue color f and by the fact that it is distinctly harder in the direction parallel ( to the length of the crystals than in the direction at right angles ter'* this.

5. Zircon. Zircon, ZrSi04, is a rather rare mineral which usually occurs in minute crystals scattered throughout a rock mass. It is found in granites, syenites, crystalline limestones, chloritic schists, etc. It is to be distinguished by its usually brown -color, hardness (7.5) and tetragonal crystallization

6. Titanite. Titanite or sphene, CaTiSiOs, is a comparatively rare mineral found as an accessory constituent in granite, syenites, gneiss, mica- and chlorite-schists and crystalline limestones. It occurs as microscopical crystals in many igneous rrH-re-

7. Magnetite. Magnetite, FoD... is widespread m its occur rence as a rock constituent. It is found in all kinds of igneous rocks, usually in small disseminated grains. It is also charac teristic of the crystalline schists and gneisses. Ordinarily it occurs in comparatively small amounts and would be classed as an ac cessory mineral but at tunes it becomes a prime constituent of the rock and may be segregated into almost pure bodies of the mineral.

It is characterized by its metallic luster, black color and streak and its strong magnetic properties.

8. Ilmenite. Ilmenite or titanic iron, FeTiOa, is a common accessory mineral onqjrring in the same wav as magnetite and frequently found associated with it. It is most commonly found in the gabbros and related rocks. It is difficult to tell it from magnetite by simple inspection.

9. Hematite. Hematite, Fe2Oais. found as an accessory mineral in the feldspathic igneous rocksjmch as granite- It occurs also in the crystalline schists. It is common in the sedimentary and metamorphic rocks and at times forms large bodies of almost

Pegmatite Dikes And Veins

pure mineral. It is the red pigment in many rocks and soils and forms the cementing material in many sandstones. It is to be recognized by its red streak.

10. Pyrite. Pyrite, FeS2, is found in small disseminated *. tals in all classes of rocks. It is characterized by its pale brass color, metallic luster, hardness (6), black streak and frequently also by its isometric crystal forms.

11. Apatite. Apatite, is found in crystals of considerable size in metamorphosed limestones. It is also com mon in microscopic crystals in all varieties of igneous rocks, and in many metamorphic ones.

In addition to the minerals listed above, the following, more rare in their occurrence, are at times found as accessory rock con stituents: rutile, iolite, scapolite, andalusite and sillimanite.

Pegmatite Dikes and Veins

In connection with the deep-seated, coarse-grained igneous rocks, especially the granites, we frequently find mineral deposits

which are known as pegmatite dikes or veins. These bodies have

the general shape and character of an igneous dike or a broad mineral vein although in certain respects they differ markedly from either of these. They are to be found running through the main mass of the igneous rock or filling fissures in the other sur rounding rocks. They are composed chiefly of the same minerals as occur in the igneous rock, but usually in very coarse crvstallizations. A granite pegmatite is therefore made up principally of quartz, feldspar and mica. The quartz and feldspar crystals may be several feet in length and the mica plates are at times more than a foot across. In addition to the coarseness of the crystallization of the minerals, these veins possess other peculiar features. The minerals nf ft pegmatite vein fnr ingtangn Iwm nnt ipporuntly been deposited in the, definite order that prevailed in the igneous. rockjruiss, rnnfol" v,a'lrQ pearly simnltftqg-

Olisjv- These vairm- will 'iKn a.t times show n rihhnnp.fl nr bflndH structure where the different minerals nenn- in rlistinrt. lftyarsjhieh lie parallel to the walls of the deposit, Their minerals are also

Manual Of Mineralogy

commonly quite irregularly distributed through the mass, so that at times the vein is composed chiefly of feldspar and again becomes nearly pure quartz. Frequently, along the central portion of the dike, cavities and openings wflT be observed into which crystals of

the different minerals project. These characteristics point to a

somewhat different origin for the pegmatite veins from that of the igneous rock with which they are associated.

No extended and detailed discussion of the theory of the origin of pegmatite veins can be given here, but it may be briefly sum marized as follows. Pegmatite veins are formed during the last stages of the cooling and solidification of a plutonic igneous rock. As an igneous magma cools and slowly solidifies, it shrinks somewhat in volume and various cracks and fissures open up throughout the mass. The pressure due to the weight of the rock forces any still fluid material from the interior of the mass up through these cracks and also into any fissures that may exist in the surrounding rocks. The filling up of these fissures both in the igneous rock it self and in the neighboring rocks constitutes a pegmatite vein. As a magma cools and its minerals crystallize, large amounts of wrater vapor are frequently set free so that the residue of the still fused rock material must contain much higher percentages of water than the original magma. Consequently it becomes in its character and behavior more like a solution than a fused mass. This would account for the peculiar features observed in pegmatite veins which differentiate them from ordinary igneous deposits.

The minerals found in pegmatite veins may be divided into three general divisions. First come those minerals which form the main mass of the deposit and which, as stated above, are the same as the prominent minerals of the igneous rock with which the pegmatite dike is associated. These are commonly quart.?. : ajeldspar which is usually either orihnrlnstp. nr miW/gf but -may be qnd a mica may be either muscovite or Motile.

Garnet is also at times in a smaller way a characteristic constituent. Second comes a series of rare minerals which are, however, quite commonly observed in pegmatite deposits, and which are char acterized by the presence in them of fluorine, boron or hydroxyl. Their presence in the veins indicates also that gases under high

Contact Metamorphic Minerals

pressures have been instrumental in their formation. The min erals of this type include hill fmmnnLinp. apatite and fluorite. A third class of minerals found in pegmatite veins includes species containing rare elements such as lithium, molybdenum, tin, niobium and tantalum, the rare earths, etc. These are minerals which are rarer still in their occurrence, but when they do occur are usually to be found in pegmatite deposits. The most important members of this group are molybdenite, levidolite. svodumene. triphylite, columbite, cassiterite and monazite. r Because of the frequent occurrence in pegmatite veins of the1 'rare minerals mentioned above, some of which are often found finely colored and well crystallized, these deposits are of particular interest to students of mineralogy. TfomnWi+A are also of commercial importance, for it is from them that most of the feld spar andmica used in the arts are~obtained. Many~beautifuTgem stones7~ as beryl and tourmaline, arc also found in them. Pegmatite veins are widely distributed in their occurrence, being almost universally found wherever plutonic igneous rocks are exposed. Important districts for pegmatite veins in thp TTm±c*l States includethi JNew England states, the Black Hills in South Dakota and Southern California.

Contact Metamorphic Minerals

When an igneous rock magma is intruded into the earth's crust, it causes through the attendant heat and pressure a greater or less alteration in the surrounding rock. This alteration, or meta morphism, of the rocks lying next to an igneous intrusion usually consists partly in the development of new and characteristic mineral species. The minerals that are formed under these conditions are known as <zmtactwcfnh mineral. s, since they are produced hy . a metamorphic change and are to be found at or near the contact. line between the rock in which they lie and an igneous rock. Any rock into which an igneous mass is intruded will be affected in a greater or less degree, the amount and character of the change de pending chiefly upon the size of the intruded mass and upon the chemical and physical character of the surrounding rock. The

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t

most striking and important contact metamorphic changes take place when the igneous rock is intruded into impure limestones. When a pure limestone is affected, it is recrystallized and converted into a marble, but without any development of new species. But, on the other hand, in the case of an impure limestone the heat and pressure caused by the igneous intrusion will serve to develop new and characteristic minerals in the rock. An impure limestone will ordinarily contain, besides the calcium carbonate of the rock, vary ing amounts of quartz, clay, iron oxide, etc. Under the influence of the heat and pressure these materials will combine with the calcium carbonate to form new minerals. For instance, the calcite and quartz may react together to form wollastonite, CaSiCh. If the limestone contains dolomite, the reaction of this mineral with gijarlz, may produce pyrnvene, (Ca,Mg).Si03. If clay is present, aluminum will enter into the reaction and such minerals as spinel, MgAl2Q4, and grossularite, Ca3Al2Si30i2, may result. If any car bonaceous materials are present, the effect of thp. metnmnrpKism may convert them into graphite. The common contact metamorphic minerals found in limestone are as follows: graphite, spinel, corundum, wollastonite, tremolite. pyroxene and the lime garnets. grossularite and andradite.

As mentioned in a preceding paragraph, an igneous rock in cool ing often gives off large amounts of mineralizing vapors. These consist largely of water vapor, but often include boron and fluorine gases. Under the influence of these vapors, other minerals are often formed in the contact zone of a limestone. These particular minerals are commonly spoken of as pneumatolytic minerals, since they are formed, partly at least, through the agency of mineral gases. They consist chiefly of calcium and aluminum silicates which contain hydroxyl, fluorine or boron. The most common of the pneumatolytic contact minerals are chondrodite, vesuvianite, scapolite, phlogopite, tourmaline andjhoorite

Veins and Vein Minerals

Most of the important, mineral deposit* qi.,Hv those .that fernislTfErvaalixi-mMls, ;irp"fniiml in pro known ac veins A brief discussion of veins and vein minerals follows.

Veins And Vein Minerals

The rocks of the earth's crust have many openings existing within them. These openings vary in size from microscopic cracks to cavities of considerable extent. The openings may be irregular and discontinuous or they may be in the form of fissures which are continuous for greater or less distances. Below a certain inconsiderable depth, these openings are largely filled by water. This underground water, as it is termed, slowly circulates through the rocks by means of the openings in them. Through a large part of its circulation, the water must exist at a high temperature and pressure, and under these circumstances becomes a strong solvent and active chemical agent. Underground water in general descends slowly through the smaller openings in the rocks, and then gradually finding its way into the bigger openings will at last enter some larger fissure and changing its course will begin to ascend. On its passage through the rocks, it will have dissolved their more soluble constituents, and when it ultimately enters the larger fissures and commences to rise will be carrying considerable amounts of dissolved mineral material. The igneous rocks in particular are important factors in furnishing underground waters with mineral constituents partly because of the effect of their heat upon its activity, and partly because they give off in the form of vapors a large amount of mineral material which ultimately gets into the underground circulation. When these mineral laden waters commence to rise in the larger fissures, they slowly come into regions of lower pressure and temperature. Under these changing conditions, the water will not be able to retain all its mineral con stituents in solution, and their points of saturation being reached various minerals will begin to crystallize out and be deposited on the walls of the fissure. In time, if the process continues, the fis sure may he comp1ptply wall tn wall xyj+b minnrrrtb

deposited in this way. Such a fiUsd fissure is knnyrn as a veim

Evidence that the minerals of a vein have been deposited from solution is given by the following facts. Often a mineral vein shows a distinctly banded or ribboned structure. That is, the different minerals occur in more or less regular layers which lie parallel to the walls. This shows that the various minerals have

Manual Of Mineralogy

not been deposited simultaneously, but in a definite order of suc cession. Again, frequently it wall be observed that the vein material has not completely filled the fissure, but that there are openings left along its central line. These openings are termed vugs and are often lined with crystallized minerals. These con ditions cannot be easily explained except on the assumption that the contents of a mineral vein have been deposited from solution.

The shape and general physical character of a vein depends upon the type of fissure its minerals have been deposited in, and the type of fissure in turn depends upon the character of the rock in which it lies and the kind of force which originally caused its for mation. In a firm homogeneous rock, like a granite, a fissure will be fairly regular and clean cut in character. It is liable to be com paratively narrow in respect to its horizontal and vertical extent and reasonably straight in its course. On the other hand, if a rock that is easily fractured and splintered, like a slate or a schist, is subjected to a breaking strain, we are more liable to have formed a zone of narrow and interlacing fissures, rather than one straight crack. In an easily soluble rock like a limestone, a fissure will often be extremely irregular in its shape and size due more or less to a solution of its walls by the waters that have flowed through it.

A typical vein consists of a mineral deposit which has filled a fissure solidly from wall to wall, and shows sharply defined boun daries. There are, however, many variations from this type. Frequently, as observed above, irregular openings termed vugs may occur among the vein minerals. It is from these vugs that we obtain many of our crystallized mineral specimens. Again, the walls of a vein may not be sharply defined. The mineralizing waters that filled the fissure may have acted upon the wall rocks and partially dissolving them may have replaced them with the vein minerals. Consequently we may have almost a complete gradation from the unaltered rock to the pure vein filling, and with no sharp line of division between. Some deposits have largely formed by the deposition of vein minerals in the wall rocks. Such ctepositsare known as replacement deposits. They are more liable to be found in the soluble rocks like limestones. There is every

Veins And Vein Minerals

gradation possible from a true vein with sharply defined walls to a replacement deposit with indefinite boundaries.

The mineral contents of a vein depend chiefly upon the chemi cal composition of the waters from which its minerals have crys tallized. There are many different sorts of veins, and many different mineral associations are observed in them. There are, however, certain minerals and associations that are more frequent in their occurrence to which attention should be drawn. The sulphideg_ nerhans the most characteristic chemical group of minerals to be found in veins. The following minerals are very common vein minerals, pyrite, FeS2, chalcopyrite, CuFeS2, galena, PhSwhaleute, ZuS, chalcocite. Cu2S, borrnte, (JiuFeSi, marcasite . FeS,. arsenopyrite, FeAsS, stibnite, Sb2S3, tetrahedrite , CusSbsS?. etc. In addition to these, which in large part comprise our ore minerals, certain nonmetallic minerals are also commonly to be observed. These being of no particular commercial value are called gangue minerals {gangue is from gang, a vein ) . They include the following : quartz, Si02, caldte, CaC03, dolomite, siderite, FeCCh, barite. BaSO..- Huorite, CaF2, rhodochrosite , MnCCh, etc.

While comparatively few positive statements concerning the associations of vein minerals can be made, the following points are of interest.

1. Gold-bearing Quartz Veins. Native gold is most com monly found in quartz veins. It may occur alone in the quartz either in nests or in finely disseminated particles, or it may occur in connection with certain sulphides in the veins. The most common sulphides found in such connections are pyrite, chalcopyrite and arsenopyrite.

2. Gold- and Silver-bearing Copper Veins. The gold and silver content of these veins is associated with the various copper sulphides. Frequently the amount of the precious metals is quite small. The chief minerals are chalcopyrite, tetrahedrite, bornite, chalcocite, pyrite and various rarer silver minerals.

3. Silver-bearing Lead Veins. Silver and lead minerals atp yprv ]y p seriated with each nth nr These veins contain such minerals as galena, argentite, tetrahedrite, sphalerite, pyrite, calcite, dolomite, rhodochrosite, etc.

Manual Of Mineralogy

4. Lead-zinc Veins. Lead and zinc minerals often occur to gether particularly in deposits that lie in limestones. The chief minerals of such deposits are galena, sphalerite, marcasite, chalcopyrite, smithsonite, calamine, cerussite, calcite, dolomite.

5. Copper-iron Veins. Hopper anr] irnn snlnhides are ouite commonly associated with each other, the prominent minerals of such veins bemg pynte, chalcopyrite, chalcocite, bomite, tetrahedrite, enargite, etc.

Primary and Secondary Vein Minerals. Secondary

Enrichment

In many mineral veins, it is obvious that certain minerals belong to the original vein deposit while certain others have been formed subsequently. These two classes of minerals are known respec tively as Primary and Secondary Minerals. The primary vein minerals are those which were originally deposited by the ascending waters in the vein fissure. The primary metallic vein minerals are comparatively few in number, the more important heinmpvrite. pjrjteTga.lena, and sphalerite. The secondary vein minerals have been formed from the primary minerals by some subsequent chemical reaction. This change is ordinarily brought about

through the influence of oxidizing waters which coming from the surface of the earth descend through the upper portions of the vein. Under these conditions, various new minerals are formed, many of them being oxidized compounds. As the descending waters lose their oxygen content within a comparatively short -distance of the earth's surface, the secondary minerals are only to be found in the upper part of a vein. Together with the formation of these secondary minerals, there is frequently a downward migration of the valuable metals in the vein. This is brought about by the solu tion of the minerals in the uppermost portion of the vein /and a subsequent reprecipitation a little farther down. As the surface of the earth is gradually lowered by erosion, the upper part of a vein is continually being worn away . 1 lut the metallic content of the uppermost, part of thr olTT,"1,rl f,nrrinrl hy

the descending oxidizing waters. In this way, the metallic content

Primary And Secondary Vein Minerals 369

of the upper part of many veins has been notably enriched since there is concentrated in this short space most of the original con tents of hundreds, perhaps thousands, of feet of the vein which have been slowly worn away by the general erosion of the country. Consequently the zone of the secondary vein minerals is also fre quently a zone of secondary enrichment. This is an important fact to be borne in mind since, because of it, the upper two or three hundred feet of a vein are ordinarily the richest portion of a deposit. The ore below that depth gradually reverts to its original unaltered and unenriched character and may frequently prove too low in value to warrant its being mined. The prevalent idea that the ore of a vein must increase in value with increasing depth is not true in the great majority of cases.

It will be of interest to consider the more important primary vein minerals and the secondary minerals that are commonly formed from them.

1. Iron Minerals. The common nrimarv vpi'n imn ™'Vml-F pynte, F eS> Marcasite, FeS2, while not so common in occurrence is also a primary mineral. When oxidized, these minerals _yi' ordinarily the .hydrated 'oxide hmonitc, FcChjOHJe. The upper portion of a vein that was originally rich in pyrite will often show a cellular and rusty mass of limonite. This limonite deposit near the surface is commonly termed gossan. The yellow rusty char acter of the outcrop of many veins enables one frequently to locate them and to trace them across the country.

2. Copper Minerals. The one common primary copper min eral is chalcopyrite, CuFeS2l At times, some of the other sulphides may be primary in their origin, but this is not generally the case. The secondary formation of bornite and chalcocite may be ex plained as follows. The copper sulphide existing in the original chalcopyrite is oxidized by the descending waters at the surface to copper sulphate which is then dissolved and carried farther down the vein. Here it comes in contact with unaltered chalcopyrite and a reaction takes place which enriches the sulphide, changing it to bornite, Cu5FeS4. Later, more copper sulphate in solution comes in contact with the bornite and a further enrichment takes place with the formation of chalcocite, Cu2S. In each case, there

Manual Of Mineralogy

is an interchange of metals, the iron in the original sulphide going into solution as a sulphate thus taking the place of the copper which has been precipitated. If the copper deposit lies in limestone rocks, we commonly find the various carbonates and oxides of copper also formed in the upper parts of the deposit. The second ary copper minerals therefore include chcdcocite, CU2S, bomite, Cu;,FeS4, native copper, Cu, cuvrite. Cu20, malachite, (Cu.OH) 2C03, azurite, chrysocolla, CuSi03.2H20, chalcanthite, CuSo4.5H20.

3. Lead Minerals. TV. primary, W1 mineral is galena. PbS. The secondary minerals of lead are all oxidized compounds and include the following: cerussite, PbC03, anglesite, PbS04, pyromorphite, wulfenite, PbMo04.

4. Zinc Minerals. SghaJgater-ZnS, is the only common pri mary zinc mineral— — The chief secondary minerals are smithsonite, ZnC03, and calamine,

5. Silver Minerals. Probably most of the sulphide minerals of silver are primary in their origin. The following minerals are "usually secondary, although native silver at times appears primary : native silver, Ag, cerargyrite, AgCl, embolite, etc.

Lists of Minerals Arranged According to Systems of Crystallization

In the following tables the minerals which are described in this book are listed according to the system of crystallization to which they belong. The order in which they are given is according to the chemical classification adopted in this book.

Isometric System: Normal Class

Elements

1. Diamond, C.

2. Gold, Au.

3. Silver, Ag.

4. Copper, Cu.

5. Platinum, Pt.

6. Iron, Fe.

List Of Minerals

Sulphides

1. Galena, PbS. 4. Bornite, Cu5FeS4.

2. Argentite, Ag. 5. Linnseite, Co3S4.

3. Pentlandite,

1. Halite, NaCl.

2. Sylvite, KC1.

3. Cerargyrite, AgCl.

Chlorides, etc.

4. Embolite,

5. Fluorite, CaF2.

Oxides

1. Senarmontite, Sb203.

2. Cuprite, Cu20.

Spinel Group, IP'R/'O. or R"0.R'"203.

3. Spinel, MgAl204.

4. Gahnite, ZnAJ204.

5. Magnetite, Fe304.

6. Franklinite, (Fe,Mn,Zn)

7. Chromite,

Silicates

1. Leucite,

2. Analcite,

3. Sodalite,

4. Lazurite,

5. Garnet Group, Grossularite, Pyrope, Almandite, Spessartite, Andradite, Uvarovite,

Ca3 (Cr , Al) 2 (Si04) 3.

Uranate

1. Uraninite, U03 and U02 with Th, Y, Ce, Pb, He, Ra.

Isometric System: Pyritohedral Class

1. Pyrite, FeS2.

2. Smaltite, CoAs2.

3. Chloanthite, NiAs2.

Sulphides, etc.

4. Cobaltite, CoAsS.

5. Gersdorffite, NiAsS.

6. Sperrylite, PtAs2.

Manual Of Mineralogy

Isometric System: Tetrahedral Class

1. Sphalerite, ZnS.

2. Tiemannite, HgSe.

Sulphides, etc.

3. Alabandite, MnS.

Sulphantimonites, Sulpharsenites

1. Tetrahedrite,

CU8Sb2S7 4Cu2S.Sb2S3.

2. Tennantite,

CusAs2S7 4Cu2S.As2Sj.

Borate

1. Boracite, Mg7Cl2Bi603o.

TETRAGONAL SYSTEM: NORMAL CLASS Sulphide

1. Stannite, Cu2FeSnS4.

Oxides and Closely Related Silicates and Phosphates

1. Octahedrite, Ti02.

2. Cassiterite, Sn02 or SnSn04.

3. Rutile, Ti02 or TiTi04.

4. Zircon, ZrSi04.

5. Thorite, ThSi04.

6. Xenotime, YP04.

Carbonate

1. Phosgenite,

Silicates

1. Vesuvianite, Complex 2. Apophyllite,

Ca,Mg,Na,Al,Fe silicate.

Tetragonal System: Tri-Pyramidal Class

Silicate

1. Wernerite or Scapolite, Ca4Al6Si8026 with Na4Al3Si9024Cl.

Tungstate and Molybdate

1. Scheelite, CaW04. 2. Wulfenite, PbMo04.

List Of Minerals

Tetragonal System: Sphenoidal Class

Sulphide

1. Chalcopyrite, CuFeS2.

Hexagonal System: Normal Class

1. Molybdenite, MoS2

2. Covellite, CuS.

Sulphides

3. Pyrrhotite, FeuSi2.

Silicates

1. Beryl, with some [OH]?.

2. Nephelite, NaAlSi04. (Approx.)

Hexagonal System: Hemimorphic Class

Sulphides, etc.

1. Greenockite, CdS. 2. Niccolite, NiAs.

Oxide

1. Zincite, ZnO with MnO.

Hexagonal System: Tri-Pyramidal Class

Phosphates, etc. Apatite Group

1. Apatite,

2. Pyromorphite,

Mimetite,

Vanadinite,

Hexagonal System: Rhombohedral Class Normal Division

Elements

1. Graphite, C. 4. Bismuth, Bi.

2. Arsenic, As. 5. Tellurium, Te.

3. Antimony, Sb.

Manual Of Mineralogy

Sulphides, Sulphantimonites, Sulpharsemtes

1. Millerite, NiS.

2. Pyrargyrite,

Ag3SbS3 or 3Ag2S.Sb2S3.

Oxides,

1. Corundum, A1203.

2. Hematite, Fe203.

3. Proustite,

Ag3AsS3 or 3Ag2S.As2S3.

Hydroxides

3. Brucite,

Carbonates

Calcite Group

1. Calcite, CaC03.

2. Dolomite,

(tri-rhombohedral) .

3. Magnesite, MgC03.

4. Siderite, FeC03.

5. Rhodochrosite, MnC03.

6. Smithsonite, ZnC03.

1. Tourmaline,

(hemimorphic).

Silicates

2. Chabazite,

Nitrate

1. Soda-niter, NaN03.

Hexagonal System: Rhombohedral Class Tri-Rhombohedral Division

Titanate

1. Ilmenite, FeTi03.

Silicates

1. Willemite, Zn2Si04. 2. Phenacite, Be2Si04.

List Of Minerals

Hexagonal System: Rhombohedral Class Trapezohedral Division

Sulphide

1. Cinnabar, HgS.

Oxide

1. Quartz, Si02.

Orthorhombic System

Element 1. Sulphur, S.

1. Stibnite, Sb2S3.

2. Bismuthinite, Bi2S3.

3. Chalcocite, Cu2S.

Sulphides, etc.

4. Stromeyerite, CuAgS.

5. Marcasite, FeS2.

6. Arsenopyrite, FeAsS.

Sulphantimonites, etc.

1. Bournonite, 2. Stephanite, Ag6SbS4 or or 5Ag2S.Sb2S3.

Sulpharsenate

1. Enargite, CujAsS or 3Cu2S.As2S5.

Chlorides

1. Atacamite, 2. Camallite, KMgCl3.6H20.

Oxides, Hydroxides

1. Chrysoberyl, BeAl204.

2. Brookite, Ti02.

3. Diaspore,

4. Goethite,

5. Manganite,

6. Pyrolusite, Mn02 with

about 2% H20. (Pseudomorphous.)

Manual Of Mineralogy

Carbonates Aragonite Group

1. Aragonite, CaC03. 3. Witherite, BaCOj.

2. Strontianite, SrC03. 4. Cerussite, PbC03.

Silicates

1. Enstatite, Bronzite,

Hypersthene, '

2.

3. Iolite,

4. Chrysolite,

5. Danburite,

6. Topaz,

7. Andalusite,

8. Zoisite,

9. Prehnite,

10. Calamine,

(hemimorphic).

11. Staurolite,

(Mg,Fe) (Al.OH)

12. Sillimanite, Al2Si06.

13. Natrolite,

Na2Al2Si30io.2H20.

14. Thomsonite

Niobate, Tantalate

1. Columbite-tantalite,

Phosphates, etc.

1. Triphylite-lithiophilite,

2. Olivenite,

3. Scorodite, FeAs04.2H20.

4. Wavellite,

Nitrate

1. Niter, KN03.

Sulphates

1. Barite, BaS04. 4. Anhydrite, CaS04.

2. Celestite, SrS04. 5. Brochantite,

3. Anglesite, PbS04.

List Of Minerals

Monoclinic System

Sulphides, Tellurides

1. Realgar, AsS. 3. Sylvanite, AuAgTe4.

2. Orpiment, As2S3. 4. Calaverite, AuTe2.

Sulphantimonite

1. Polybasite, Ag9SbS6.

Fluoride

1. Cryolite, Na;iAlF6.

Hydroxide

1. Gibbsite,

Carbonates

1. Malachite, 4. Gay-Lussite,

2. Azurite, Na2C03.CaC03.5H20.

3. Aurichalcite,

Silicates

1. Orthoclase, KAJSi3Os.

2. Pyroxene Group, R"SiO:

(R Ca,Mg,Fe).

4. Jadeite,

5. Spodumene,

6. Wollastonite, CaSi03.

7. Pectolite,

8. Amphibole Group,

Ca,Mg,Fe).

9. Datolite,

10. Epidote,

11. Allanite,

CaAl.OH) (Al,Fe,Ce,La,Di)

Hydrated Silicates

1. Heulandite,

2. Harmotome,

3. Stilbite,

4. Laumontite,

H4CaAl2Si40I4.2H20.

5. Scolecite,

CaAl2Si3Oio.3H20.

Manual Of Mineralogy

Foliated, Micaceous Silicates

1. Muscovite,

2. Lepidolite,

KLi ( AI .2 (OH,F) ) A1 (Si03) 3.

3. Biotite,

4. Phlogopite,

5. Lepidomelane,

6. Margarite, H2CaAl4Si20i2.

7. Clinochlore, Chlorite,

8. Serpentine, H4Mg3Si209.

9. Kaolin, HaShOj.

10. Talc,

11. Pyroph}'llite,

Titanosilicate 1. Titanite, CaTiSiOs.

Phosphates

1. Monazite, 3. Vivianite,

with ThSi04.

2. Lazulite,

Mg (Al .OH) 2 (P04) 2.

1. Colemanite,

Ca2B60n.5H20.

Borates

2. Borax, Na*B4O7.10HiO.

Sulphates,

Glauberite, Crocoite, PbCr04.

Chromates

3. Gypsum, CaS04.2H20.

Tungstates

1. Wolframite, FeW04 2. Hiibnerite, MnW04.

Triclinic System

Silicates

1. Microcline, KAlSi30$.

Plagioclase Feldspars.

2. Albite, NaAlSi308.

3. Oligoclase, 3 Albite, 1 Anor-

thite.

4. Andesine, 1 Albite, 1 Anor-

thite.

5. Labradorite, 1 Albite, 3

Anorthite.

6. Anorthite, CaAl2Si208.

7. Rhodonite, MnSi03.

8. Cyanite, Al2Si06.

9. Axinite,

List Of Minerals

Phosphate

1. Amblygonite,

Sulphate

1. Chalcanthite, CuS04.5H20. AMORPHOUS OR MASSIVE MINERALS

Oxides, Hydroxides

1. Opal, Si02, generally with 3

to 9% H20.

2. Turgite,

3. Limonite,

4. Bauxite,

5. Psilomelane, Mn02 with

MnO, BaO, CoO, H20, etc.

1. Genthite, Garnierite, Ni,Mg, silicates.

Silicates

2. Chrysocolla, CuSi03.2H20.

Phosphate

1. Turquois, with

V. Determinative Mineralogy

Introduction

Determinative Tables for minerals are of two kinds: (1) those which rely chiefly upon chemical tests, and (2) those which make use solely of physical tests. Obviously, since the chemical com position of a mineral is its most fundamental property, those tables which emphasize chemical tests are much the more satis factory. On the other hand, the tables which depend wholly upon physical tests have distinct limitations beyond which it is impossible to use them. These latter tables have, however, the important advantages that their tests are simpler, more readily and quickly performed, and do not require the equipment of a laboratory. For these reasons physical determinative tables probably have a wider use, in spite of their limitations, than those that involve chemical tests.

The character and purpose of this book forbid the inclusion of elaborate chemical tables and require instead the introduction of physical tables of as simple a form as possible. Such tables must, however, be used with a thorough understanding of their nature and their inherent disadvantages. Many of the physical properties of minerals are not entirely fixed in their character. Color, for instance, is frequently an extremely variable property. Hardness, while more definite, may vary to a slight extent, and by a change in the structure of a mineral may appear to vary much more widely. Cleavage is a property which may often be obscured by the physical condition of the mineral. Consequently in making a determinar tion of a mineral by means of its physical properties alone, it is necessary to have a fairly typical specimen and one which is of sufficient size to enable its characters to be definitely seen. Often, moreover, it will be impossible by the aid of such tables to posi tively differentiate between two or three similar species. Fre quently, however, in such cases the descriptions of these possible

Determinative Mineralogy

minerals given in Section IV will enable one to make a definite decision. Moreover, the tables that follow, used in connection with the chemical tests given under the description of minerals in Section IV, together with the more detailed explanations of the various tests to be found in Section III, may serve as a substitute for more elaborate chemical tables.

The Determinative Tables given beyond have been made as brief and simple as possible. Only the common species or those which, while rarer in occurrence, are of economic importance have been included. The chances of having a mineral to determine that is not included in these tables are small, but it must be borne in mind that there is such a possibility. The names of the minerals have been printed in three different styles of type, as (see page 389) chalcocite, argentite and Stephanite, in order to indicate their relative importance and frequency of occurrence. Whenever it was felt that difficulty might be experienced in correctly placing a mineral, it has been included in the two or more possible divisions. Usually, however, for the sake of brevity, the detailed description of such a mineral has been printed in full only upon one page.

On page 385 will be found a General Classification of the tables. The proper division in which to look for a mineral is to be deter mined by means of the tests indicated there. The tables are divided into two main sections depending upon the luster of the minerals in them. The first division includes those minerals which have a Metallic or Submetallic Luster. By that is meant those minerals which on their thinnest edges remain opaque and which consequently will give black or dark-colored "streaks" when they are rubbed across a piece of unglazed porcelain, the socalled streak plate. Nonmetallic minerals are those which are transparent upon their thinnest edges, and which therefore give either a colorless or a light-colored streak. It is to be noted that the color of the streak cannot always be foretold from the color of the mineral itself. Frequently a dark-colored mineral will be found to give a light-colored streak.

The tables are next subdivided according to hardness. The tests used in the General Classification are: (1) minerals that are soft enough to leave a mark when rubbed across a piece of paper;

Manual Of Mineralogy

(2) minerals that can be scratched by the finger nail; (3) those that can be cut by a cent; (4) minerals that are softer than the steel of the blade of an ordinary pocket knife; (5) and (6) min erals that are harder than a knife but can or cannot be scratched by quartz. In applying the tests for hardness, certain precautions should be observed. Before deciding upon the relative hardness of a mineral, it is well to try the test if possible in two ways. For instance, if a mineral is apparently scratched by the edge of a cent make sure on the other hand that the cent cannot be scratched by the mineral. Further, the cent and the knife blade used in making the tests should be bright and clean, otherwise the rubbing off of a layer of dirt or tarnish might be mistaken for a scratch. In the tables themselves, the hardness of the minerals is given in terms of the Scale of Hardness, see page 68. The possession of specimens of the minerals of this scale, so that the hardness of a mineral could be closely determined, would frequently be of great assistance in the use of the tables. Lastly, it is to be remembered that the physical condition of a mineral may apparently change its hardness. For instance, minerals that occur at times in pulverulent or fibrous forms will under these conditions appear to be much softer than when in their more usual form. Also the chemical alteration of a mineral will commonly change its hardness.

The minerals with nonmetallic luster are, in general, further subdivided according to whether they show a prominent cleavage or not. This will frequently be a difficult decision to make. It will require some practice and experience before one can always make the determination rapidly and accurately. Note that the minerals are divided according to whether they show a prominent cleavage or not. Minerals in which the cleavage is imperfect or ordinarily obscure are included with those that have no cleavage. It will always be best, if it is possible, to actually try to produce a cleavage upon the specimen rather than to judge from its appear ance alone. If a mineral shows a cleavage, the number of the cleavage planes, their relations to each other and to any crystal forms present, etc., are to be noted. As far as possible, the min erals in which the cleavage may become obscure, because of certain conditions of structure, have been included in both divisions.

Determinative Mineralogy

The minerals which fall in any one of the different divisions of the tables have been arranged according to various methods. In some cases, those that possess similar cleavages have been grouped together; frequently color determines their order, etc. The column farthest to the left will indicate the method of arrangement used in each section. Most of the different properties listed and the more general facts included under the headings, Crystallization and Structure and Remarks, need no especial explanation. A few words, however, may be said concerning the column headed Specific Gravity. For a discussion of specific gravity and the methods for its accurate determination, see page 69. If the specimen to be determined is of sufficient size and is pure, its approximate specific gravity can be determined by simply weighing it in the hand. In order to do this, however, will require some experience. Below is given a list of common minerals which show a wide range of specific gravity. By experimenting with specimens of these, one can become quite expert in the approximate determination of the specific gravity of any mineral.

Halite, 2.14 Gypsum, 2.32 Orthoclase, 2.56 Calcite, 2.72 Fluorite, 3.18 Topaz, 3.53

Limonite, 3.80 Corundum, 4.03 Chalcopyrite, 4.20 Barite, 4.48 Pyrite, 5.03 Chalcocite, 5.75

Cerussite, 6.51 Cassiterite, 6.95 Galena, 7.50 Cinnabar, 8.10 Copper, 8.84 Silver, 10.60

When the subdivisions of the tables are studied, the following interesting and important facts are to be noted. The majority of the minerals with metallic luster are sulphides. Most of them are softer than a knife. The only sulphides that are harder than a knife are Pyrite, Marcasite and Arsenopyrite. The greater part of minerals with metallic or submetallic luster that are harder than a knife are oxygen compounds of iron. Among the minerals with nonmetallic luster, it is to be noted that those which are harder than a knife are, with very few exceptions, either silicates or oxides. Comparatively few silicates are to be found among the minerals of nonmetallic luster which are softer than a knife. It is

Manual Of Mineralogy

to be further noted that the majority of such silicates contain water in some form. On the other hand, the greater part of the carbonates, sulphates, phosphates, etc., are to be found in these sections.

General Classification Of The

Tables

A. Metallic Or Submetallic Luster

I. Very Soft. Will Readily Leave a Mark on Paper,

p. 386.

II. Can be Scratched by a Knife, but Will not Readily Leave a Mark on Paper, p. 388.

III. Cannot be Scratched by a Knife, p. 398.

B. Nonmetallic Luster

I. Minerals which Give a Definitely Colored Streak,

p. 402.

II. Minerals which Give a Colorless Streak.

1. Can be scratched by the finger nail, p. 408.

2. Cannot be scratched by the finger nail, but can

be scratched by a cent.

a. Show a 'prominent cleavage, p. 412. h. Do not show a prominent cleavage.

1. A small splinter is fusible in the candle

flame.

a. Readily soluble in water; yield a

taste, p. 414.

b. Insoluble in water, p. 416.

2. Infusible in the candle flame, p. 416.

3. Cannot be scratched by a cent, but can be scratched

by a knife.

а. Show a prominent cleavage, p. 418.

б. Do not show a prominent cleavage, p. 426.

4. Cannot be scratched by a knife, but can be

scratched by quartz.

a. Show a prominent cleavage, p. 430. h. Do not show a prominent cleavage, p. 436.

5. Cannot be scratched by quartz.

a. Show a prominent cleavage, p. 442.

b. Do not show a prominent cleavage, p. 444.

Metallic Or

I. Very soft. Will readily

Streak.

Color.

Hardness.

Cleavage and [ Fracture.

Spec.

Grav.

Iron-black.

2-2.5. Marks paper easily.

F. Splintery.

Black.

Steel-gray to iron-black.

1-1.5. Marks paper easily.

One perfect C.

1-1.5. Marks paper easily.

One perfect C.

Gray-black.

Blue-blaclc or lead-gray.

2. Marks paper easily.

One perfect C.

2.5. Marks paper with difficulty.

Perfect cubic C.

Bright red.

Red to vermil ion.

Marks paper with difficulty.

Red-brown.

Red-brown.

Marks paper eas ily.

Yellow-brown

Yellow-

brown.

Marks paper eas ily.

3 6-4 0

See also eovellite, p. 393, and argentite, p. 389,

Submetallic Luster.

leave a mark on paper.

Crystallization and Structure.

Remarks.

Name and Composition.

Usually radiating fibrous or splintery.

Distinguished from other minerals of this group by its structure.

Pyrolusite.

Mn02.

Rhombohedral. Micaceous.

May be in hexagonal-shaped leaves. Told lrom molybdenite by the brown tinge to its black color. Greasy feel.

Graphite.

Hexagonal. Micaceous.

May be in hexagonal-shaped leaves. Told from graphite by the blue tinge to its black color and its higher specific gravity. Greasy feel.

Molybdenite.

MoS2.

Orthorhombic. B 1 a d e d structure or in slender radi ating crystals.

Characterized by its long and bright cleavage faces. Fuses in the candle flame.

Stibnite.

Sb2S3.

In cubic crystals or cleavage masses.

See p. 391.

Galena.

PbS.

Earthy.

The earthy form of cinnabar is not common.

Cinnabar.

HgS.

Earthy.

The earthy form of hematite is often known as red ochre or paint ore.

Hematite.

Fe2Os.

Earthy.

The earthy form of limonite is often known as yellow ochre.

Limonite.

which may leave a slight mark on paper.

METALLIC OR II. Can be scratched by a knife,

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Soft black.

Iron-black.

2—2 5. Very soft. Will mark paper.

F. Splintery.

Black, with sometimes a brown tinge.

Iron-black.

5-6. U. harder than knife.

F. Irregular.

Gray-black

Steel-gray on fresh surface, tarnishing to dead black on exposure.

F. Irregular.

Black, with sometimes a brown tinge.

Steel-gray, some times tarnishes to dead black on ex posure.

F. Irregular.

C. Perfect prismatic. F. Uneven.

F. Uneven.

F. Uneven.

Black.

Gray-black.

F. Uneven.

F. Uneven.

F. Fibrous

Submetallic Luster.

but will not readily leave a mark on paper.

Crystallization and Structure.

Remarks.

Name and Composition.

Usually radiating fibrous or splintery.

Usually to be told by its struc ture and soft black streak.

Pyrolusite.

Mn02.

See p. 401.

Psilomelane.

Mn02 with MnO, etc.

Orthorhombie. Compact massive.

Often associated with other cop per ores, such as bornite, chalcopyrite, malachite, etc.

Chalcocite

(Copper Glance). CujS.

Isometric, tetrahedral. Massive or in tetrahedral crystals.

Often associated with chalcopyrite, pyrite, silver ores, etc.

Tetrahedrite

(Gray Copper). 4Cu2S.Sb2S3.

Orthorhombic. In bladed masses, showing long cleav age faces. More rarely in stout prismatic crystals.

A rare mineral, found usually with other copper minerals.

Enargite.

3Cu2S.AS2Ss.

Isometric. Usually irregu lar massive or earthy. At times in small isometric crystals, commonly cubes.

Distinguished by being easily sectile, i.e., it can be cut with a knife, like lead. Bright steelgray on fresh surface but tarnish ing to a dull gray-black on expos ure.

Argentite.

Ag2S.

Orthorhombic. In small ir regular masses, often earthy. At times in stout six-sided prismatic crystals.

© A rare mineral. Bright £ steel-gray on a fresh sur- 33 face but tarnishing to a © dull gray-black on expos- -o ure. a cj

Stephanite.

5Ag2S.Sb2S3.

Monoclinic. Often in thin six-sided crystal plates with triangular markings on top. Also massive and earthy.

A rare mineral.

Polybasite.

Irregular massive.

"O

c A rare mineral. To be positively told only by chemical tests.

.£

Stromeyrite.

In fibrous, feather-like masses.

ex

$ Characterized usually by P its fibrous structure.

Jamesonite (Feather ore). 2PbS.Sb,S„

Metallic Or

II. Can be scratched by a knife, but will

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Black.

Gray-black.

F. Uneven.

F. Uneven.

Gray-black.

Blue-black or lead-gray.

Will leave a mark on paper.

One perfect cleavage.

2.5. Marks paper with difficulty.

Perfect cubic cleavage.

Tin-white, tar nishing to dark gray.

One good cleavage but seldom seen.

Tin- white.

One good cleavage seen in the more coarsely crystallized type.

Perfect prismatic cleavage in 3 direc tions.

6. 1-6. 3

Submetallic Luster.

not readily leave a mark on paper. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic. In stout sixsided prismatic crystals. Often twinned with reen trant angles, giving a "cog wheel " effect. Also mas sive granular.

Commonlycalled " cog-wheel ore" because of the characteristic group ing of its crystals. Easily fusible in the candle flame. Not to be positively identified when massive except by chemical tests.

Bournonite.

2PbS.Cu2S.Sb2Sa.

Tetragonal. Irregular mas sive.

Decrepitates violently in the can dle flame. Sometimes shows a bluish tarnish.

Stannite (Tin Pyrites). Cu2S.FeS.SnS2.

Orthorhombic. Bladed structure or in slender radi ating crystals.

Characterized by its long bright cleavage faces. Fuses easily in the candle flame.

Stibnite.

Sb2S3.

Orthorhombic. In long slender crystals, often radi ating. Frequently bladed.

Fuses in candle flame. A rare mineral. To be positively told from stibnite only by a test for bis muth.

Bismuthinite.

Bi2S3.

Isometric. Crystallized or (cleavable) granular.

If a small fragment is held in a candle flame it does not fuse but is slowly reduced and small globules of metallic lead collect upon the surfaces.

Galena.

PbS.

Rhombohedral. Usually fine granular, often with botryoidal structure.

Tarnishes more readily than the other similar minerals. Heated in the candle flame does not fuse but gives off a white smoke and yields a strong garlic odor. A rare min eral.

Arsenic.

As.

Rhombohedral. Usually fine granular.

Usually bright in luster. Heated in candle flame does not fuse read ily, gives off a white smoke but no odor. A rare mineral.

Antimony.

Sb.

Rhombohedral. In cleav able masses.

Characterized by bright luster and prominent cleavage. Heated in candle flame fuses very easily. A rare mineral, often associated with the gold and silver tellurides. See under sylvanite, below.

Tellurium.

Te.

METALLIC OR II. Can be scratched by a knife, but will

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Gray-black.

Tin-white.

One perfect C.

F. Uneven.

Usually pale cop per-red. Seep. 398.

F. Uneven.

Brownish bronze but when exposed to the air rapidly takes on a purple tarnish.

F. Uneven.

F. Uneven.

Brownish bronze.

Black.

C. Octahedral.

Brass-yellow.

F. Uneven.

Brass-yellow, al most greenish when in very slender crystals.

F. Uneven.

C. Rhombohedral but seldom seen.

Indigo-blue, may tarnish to blueblack.

Perfect basal C.

See also wolframite, p. 395, which may give nearly a black streak.

Submetallic Luster.

not readily leave a mark on paper. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. In thin lathshaped crystals. Often as thin coatings on surfaces of rock arranged like ancient forms of writing.

Fuses very easily in candle flame. A rare mineral. Often to be posi tively told from tellurium and the other similar tellurides only by chemical tests (see p. 169).

Sylvanite.

Monoclinic. In irregular small masses or in thin, deeply striated lath-shaped crystals.

Easily fusible in candle flame. Takes on at times a faint yellow color. A very rare mineral. Told from tellurium and sylvanite by its lack of cleavage, but for positive identification may need chemical tests.

Calaverite.

Hexagonal, hemimorphic. Massive.

See p. 399.

Niccolite.

Isometric. Massive.

Recognized usually by its promi nent purple tarnish. Associated with other copper ores, chiefly chalcocite and chalcopyrite.

Bornite.

Cu6FeS4.

Hexagonal. Massive.

Recognized usually by its charac teristic color. Small fragments often magnetic. Often associated with chalcopyrite and pyrite. Frequently carries nickel.

Pyrrhotite.

Isometric. Granular.

A rare mineral resembling closely pyrrhotite, with which it is inti mately associated. Distinguished from pyrrhotite by its cleavage.

Pentlandite.

Tetragonal, sphenoidal. Us ually massive. Sometimes in small tetrahedral-shaped crystals.

Usually recognized by its color and softness. Associated with pyrite, chalcocite, bomite, etc.

Chalcopyrite

(Copper Pyrites). CuFeSj.

Rhombohedral. In radiat ing groups of hairlike crys tals.

Commonly called capillary pyrites

Millerite.

NiS.

Hexagonal. In platy masses or in thin six-sided platy crystals.

A rare mineral. Characterized chiefly by its color. Tarnishes to blue-black on exposure. Mois tened with a drop of water turns purple.

Cove Hite.

CuS.

Metallic Or

II. Can be scratched by a knife, but will

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Dark-brown to black.

See also psilo

Steel-gray to ironblack.

One good C.

F. Splintery.

Iron-black to brownish black.

melane and tetrahe

5 . 5. Scratched by knife with diffi culty if at all.

drite, p. 389, which

F. Uneven.

One good C.

F. Uneven.

may give brown-black

7. 2-7. 5

streaks.

Light to dark brown.

Dark brown to coal-black.

Perfect C. in six direc tions (dodecahedral).

Red-brown.

Indian-red.

Dark brown to steel-gray to black.

5. 5-6. 5. Softer in some earthy vari eties but usually harder than a knife.

F. Uneven or fibrous.

F. Splintery.

Deep red to black.

C. Rhombohedral.

F. Conchoidal.

Red-brown to deep red. Rubyred in transparent variety.

F. Uneven.

Submetallic Luster.

not readily leave a mark on paper. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic. In radiating fibrous or crystalline masses Sometimes in distinct pris matic crystals, often grouped in bundles.

Often closely resembles pyrolusite with which it is frequently associ ated, but is to be distinguished from the latter by its greater hard ness and dark-brown streak.

Manganite.

Mn203.H20.

Usually in granular masses.

See p. 401 .

CHROMITE (Chromic Iron). FeCr204

Fe0.Cr203.

Monoclinio. In bladed masses. Granular to mas sive.

Characterized by bladed structure showing good cleavage parallel to length of crystal. As the amount of manganese contained in the min eral increases it becomes browner in color and streak and graduates toward hiibnerite, MnW04.

Wolframite.

(Fe.

Isometric, tetrahedral. Usually cleavable granular.

Most sphalerite is nonmetallic and strongly resinousin its luster. With increase in the amount of iron pres ent it becoires dark brown to black. The darker varieties can often be told by scratching a cleav age surface with a knife and noting the reddish mark left. The color of the streak is always much lighter than the color of the speci men.

Sphalerite

(Zinc Blende, Black Jack, etc.).

See p. 401.

Hematite.

See p. 401.

Turgite.

2F62O3.H2O.

Rhombohedral. Irregular massive.

The dark Ruby Silver, showing dark ruby color in thin splinters. See p. 403.

Pyrargyrite.

3Ag2S.Sb2S3.

Isometric. Massive or rarely in isometric crystals, cubes or octahedrons. Sometimes in very slender crystals (chalcotrichite or plush cop per).

Characterized by its submetallic luster and red streak. Associated with other copper minerals, espe cially malachite and native copper.

Cuprite.

Cu20.

METALLIC OR II. Can be scratched by a knife, but will

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Yellowbrown. Yel low ocher.

Dark brown to black.

5-5.5. Softer in some varieties but usually harder than a knife.

F. Splintery.

One good C.

F. Splintery.

Dark red.

Dark red to ver milion.

2-2.5. Some earthy varieties are soft enough to mark paper.

F. Uneven.

Prismatic C., seldom seen.

Copper-red,

shiny.

Copper-red, black tarnish.

F. Hackly.

Silver-white,

shiny.

Silver-white, gray to black tarnish.

F. Hackly.

Gray, shiny.

Whitish, or steelgray.

F. Hackly.

Silver-white,

shiny.

Silver-white w'ith a reddish tone.

Perfect basal and rhombohedral C.

Gold-yellow,

shiny.

Gold-yellow.

F. Hackly!

Olive-green.

Iron-black with a brown tarnish.

C. Cubical.

Submetallic Luster.

not readily leave a mark on paper. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

See p. 403 .

Limonite

(Bog Iron Ore).

2Fe203.3H20.

See p. 403.

Goethite.

FeO (OH) Fe203.H20.

Rhombohedral. Usually fine granular or earthy.

Usually impure and of a dark-red or brown color. When pure is trans lucent to transparent, and of a bright red color. Very heavy.

Cinnabar.

HgS.

Isometric. Usually in irreg ular grains. Ma> be in branching crystal groups or in rude isometric crystals.

A metal. Malleable. Very heavy.

Copper.

A metal. Malleable. Very heavy.

Silver.

Ag.

Isometric. Irregular grains or nuggets.

A metal. Malleable. Very heavy. Unusually hard for a metal. Very rare.

Platinum.

Pt.

Rhombohedral. In cleavable granular masses.

A metal. Sectile. When ham mered out is at first malleable but soon breaks up into small pieces. Easily fusible in the candle flame. A rare mineral.

Bismuth.

Bi.

Isometric. In irregular grains, nuggets, leaves, etc.

A metal. Malleable. Very heavy.

Gold.

Au.

Isometric, tetrahedral. In granular cleavable masses.

rare mineral. Characterized by ts brown tarnish, olive- green streak and cubical cleavage.

Alabandite.

MnS.

METALLIC OR III. Cannot be scratched

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Black.

Silver or tin white.

F. Uneven.

F. Uneven.

F. Uneven.

F. Uneven.

Usually pale cop per-red. Some times almost sil ver-white with pink tone.

F. Uneven.

Pale brass-yellow.

F. Uneven.

Pale yellow to al most white. Yellowish tarnish.

F. Uneven.

Black.

F. Uneven. At times shows octahedral part ing.

SUBMETALLIC LUSTER, by a knife.

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic. Massive granular. Sometimes in crystals.

When crystallized is commonly found in diamond-shaped tabular crystals with striations running parallel to the shorter diagonal ol the diamond. Sometimes in fan shaped twins.

Arsenopyrite

(Mispickel).

Isometric, pyritohedral. Massive.

Rare minerals found with other co balt and nickel species.

Smaltite-

Chloanthite.

Isometric, pyritohedral. Usually massive.

Rare minerals found with other co balt and nickel species. Cobaltite shows a faint reddish tone to its silver color.

Cobaltite-

Gersdorffite.

Isometric. In fine granular masses or in small octahe dral crystals.

A rare mineral.

Linnaeite.

Hexagonal, hemimorphic. Massive.

Recognized chiefly by its color and streak. A rare mineral found with other nickel and cobalt ores.

Niccolite.

Isometric, pyritohedral. Massive granular. Often in striated cubes, octahedrons, pyritohedrons, etc.

Most common sulphide. Will strike fire with steel.

Pyrite

(Iron Pyrites).

FeS2.

Orthorhombic. Often in ra diating fibrous masses. In crystal groups.

Found in nodules and stalactites. Not nearly so common as pyrite. Usually distinguished from pyrite by its lighter color and character istic crystals, but it may require a chemical test to positively differ entiate them (see p. 168).

MARCASITE (White Iron Py rites).

FeS,.

Isometric. Usually coarse to fine granular. At times in crystals, usually octahe drons.

Strongly magnetic. No other min eral exhibits this property as strongly.

Magnetite.

Fe304.

METALLIC OR III. Cannot be scratched

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Very dark brown to black.

Black.

F. Uneven.

F. Uneven.

Black.

F. Uneven.

F. Uneven.

Dark brown.

Iron-black to brownish black.

One good C.

F. Uneven.

7. 2-7. 5

F. Uneven.

F. Uneven.

Red-brown.

Indian-red.

Dark brown to steel-gray to black.

5. 5-6. 5.

Softer in some earthy varieties.

F. Uneven or fibrous.

F. Splintery.

Submetallic Luster.

by a knife. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Isometric. Massive granu lar. Small botryoidal Rarely in octahedral crys tals.

Characterized by its black color and pitchy luster. Rare. The

mineral in which the rare elements helium and radium have been found.

Uraninite (Pitch Blende). Uncertain composi tion. Chiefly oxides of uranium.

Rhombohedral. In grains as sand; massive granular; platy crystals.

Sometimes slightly magnetic. Often associated with magnetite.

ILMENITE (Titanic Iron). FeTiOj with Fe2Os. Sometimes much

Mg.

Compact massive, some times stalactitic or botryoi dal.

Dull-black luster. Often associ ated with other manganese ores from which it is told by its greater hardness.

Psilomelane. Uncertain composi tion. Mn02 with MnO, H20, BaO, K20, etc.

Orthorhombic. Granular or in stout prismatic crystals.

Black shiny luster on fresh surface. Sometimes takes on a slight bluish tarnish.

Columbite- Tantalite.

with

In bladed masses.

See p. 306.

Wolframite.

Isometric. Usually in granu lar masses. Rarely in small octahedral crystals.

Characterized often by a pitchy luster and accompanied frequently by traces of a yellow oxidation product.

CHROMITE. (Chromic Iron). FeCr204.

Isometric. Granular or in octahedral crystals.

Occurs at Franklin Furnace, N. J., usually in intimate association with zincite (red) and willemite (green).

Franklinite.

Rhombohedral. Radiating, reniform, crystallized, mica ceous.

Recognized usually by its red- 3rown streak. When in fibrous

mammillary forms cannot be posi tively told from the rare mineral urg'ite except by proving the ab sence of water in its composition by renting in a closed tube.

Hematite.

Fe202.

Radiating reniform and sta lactitic.

A rare mineral usually associated with limonite. For positive iden tification see above.

Turgite

(Hydro-hematite).

2Fe203.H20.

METALLIC OR III. Cannot be scratched

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Yellow-

brown.

Dark brown to black.

Softer in some earthy varieties.

F. Splintery.

One good C.

F. Splintery.

NONMETALLIC I. Give a definitely

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Dark red.

Dark red to Ver million.

F. Uneven.

Red-brown. Ruby-red when transparent.

F. Uneven.

Red-brown.

Indian-red.

Dark brown to steel-gray, to black.

5. 5-6. 5.

F. Splintery.

Deep red to black.

F. Conchoidal.

Bright red.

Ruby-red.

F. Conchoidal.

Submetallic Luster.

by a knife. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Radiating fibrous in mam millary or stalactitic forms.

Characterized by its streak and structure. Not always to be posi tively told from the rarer mineral goethite, except by an estimation of the water present. Limonite con tains 15%, goethite 10% of water.

Limonite

(Bog Iron Ore).

Fe,0,(0H),=

2Fe203.3H20.

Orthorhombic. Radiating fibrous in mammillary or stalactitic forms. Some times in groups of slender radiating crystals. More rarely in distinct prismatic crystals.

Told definitely from limonite if it shows cleavage or any crystal struc ture. Otherwise to be distin guished only as described above.

Goethite.

F60O3.H2O.

LUSTER, colored streak.

Crystallization and Structure.

Remarks.

Name and Composition.

Rhombohedral. Usually fino granular or earthy.

See p. 396.

Cinnabar.

HgS.

Usually massive.

See p. 395.

CUPRITE (Ruby Copper). Cu20.

Reniform, crystalline, mica ceous, earthy.

See p. 401.

Hematite.

F02O3.

Reniform and stalactitio.

See p. 401.

Turgite.

2Fe20s.H2O.

Rhombohedral. Irregular massive. Rarely in crystals.

The dark " ruby silver " showing dark ruby-red color in thin splin ters. A rare mineral associated with proustite, stephanite, polybassite, argentite, etc. Easily fusible in the candle flame.

Pyrargyrite.

3Ag2S.Sb2S2.

Rhombohedral. Irregular massive. Rarely in crystals.

The light " ruby silver." Charac- :erized by its color and adamantine uster. Rare, with associations ike those of pyrargyrite. Easily usable in the candle flame.

Proustite.

3Ag2S.As2Sa.

NONMETALLIC I. Give a definitely

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Yellow-

brown.

Dark brown to black.

5-5.5. Softer in some varieties but usually harder than a knife.

F. Splintery.

3 6-4 0

One good C.

F. Splintery.

Brown.

Dark brown.

One good C.

F. Uneven.

7 2-7 5

Light brown.

Light to dark brown.

Perfect C. In 6 direc tions (dodecahedral).

Light orange to dark brown.

Orange- yellow, brown, black.

Prismatic C.

4 8-5 2

Light

brown.

Brown to black.

F. Uneven.

6 8-7 1

Light

brown.

Reddish brown to black.

F. Uneven.

C. Not prominent.

Orange-yel

low.

Deep red to or ange-yellow.

C. Basal.

Bright red.

F. Uneven.

Deep red.

1.5-2. Can be scratched by fin ger nail.

F. Conchoidal. One C., not prominent.

Luster.

colored streak. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Mammillary or stalactitic.

See p. 403.

Limonite

(Bog Iron Ore).

2Fe203.3H20.

Mammillary or stalactitic. Radiating groups of slender crystals.

See p. 403 .

Goethite.

Fe203.H20.

Monoclinic. In b 1 a d e d

masses.

See p. 395.

Wolframite.

Isometric; tetrahedral. I n granular cleavable masses or in rounded crystals.

Characterized by its resinous luster and perfect cleavage. See p. 395.

Sphalerite.

ZnS.

Tetragonal. In prismatic crystals; also massive, com pact.

A rare mineral.

Thorite.

Tetragonal. In irregular masses; in compact fibrous reniform structure; in rolled grains. Rarely in prismatic crystals. Commonly twinned.

Very heavy. Usually opaque to translucent. Occurs as rolled grains in sand; in pegmatite veins and in granite rocks.

Cassiterite

(Tin Stone).

Tetragonal. In prismatic crystals vertically striated; often slender acicular. Fre quently twinned.

Rutile.

Hexagonal ; he m i m o r p h i c. Granular cleavable.

Characterized by its color, streak and cleavage. Found at Franklin Furnace, N. J., often intimately as sociated with franklinite (black) and willemite (green).

Zincite.

Monoclinic. In long slender crystals, often in interlacing groups.

Characterized by its color and high luster. Decrepitates in the candle flame.

Crocoite.

Monoclinic. Crystallized or Easily fusible in the candle flame, earthy. [Characterized by its color and

when in crystals by its resinous duster.

Realgar.

AsS.

Nonmetallic

I. Give a definitely

Streak.

Color.

Hardness.

Cleavage and Fracture.

Spec.

Grav.

Pale yellow.

Lemon-yellow.

1 . 5-2. Can be scratched by fin ger nail.

One prominent C.

Pale yellow.

1.5-2. 5.

F. Conehoidal or un even.

Light yal lowgreen.

Blackish,

olive-green,

brown.

F. Uneven.

Light green.

Dark emeraldgreen.

%

One good C.

One good C.t not com monly seen.

Bright green.

One good C., rarely seen.

Light blue.

Intense azure-blue.

F. Conehoidal or un even.

F. Conehoidal.

Very light blue.

Light green to turquois blue.

F. Uneven.

2. 0-2. 4

Grayish blue.

Verv dark blue. Bluish green.

One good C.

2. 6-2. 7

See also lazurite, p. 431. which may give a very light blue streak,

40G

Luster.

colored streak. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. In cleavable masses.

Easily fusible in the candle flame. Characterized by its cleavage, color and resinous luster.

Orpiment.

A82S3.

Orthorhombic. In crystals. Granular crystalline. Earthy.

Burns with a blue flame giving a strong odor of sulphur dioxide. A poor conductor of heat. A mass held in the hand close to the ear will be heard to crackle on account of the irregular expansion due to the heat of the hand. Often earthy and impure.

Sulphur.

S.

Orthorhombic. In aggre gates of small crystals.

Characterized by its color and small prismatic crystals.

Olivenite.

Cu

Orthorhombic. In granular cleavable masses or in small prismatic crystals.

Characterized by its dark green color and good cleavage.

Atacamite.

Orthorhombic. In small prismatic crystals or in gran ular masses.

Characterized by its green color and slender prismatic crystals.

Brochantite.

CuSO<. 3Cu

Monoclinic. Radiating fi brous, mammillary.

Characterized by its bright green color and radiating fibrous struc ture. Effervesces when a drop of cold acid is placed on the specimen.

Malachite.

CuCOj.Cu

Monoclinic. In small crys tals, often in groups. Radi ating fibrous, mammillary.

Characterized by its intense blue color. Effervesces when a drop of cold acid is placed on the specimen.

Azurite.

Triclinic. In crystals. Mas sive, stalactitic. Sometimes with fibrous appearance.

Soluble in water. Metallic taste. Characterized by color. Product of oxidation of copper sulphides.

Chalcanthite.

(Blue Vitriol). CuS04.5H20.

Massive and amorphous.

Characterized by its structure and color. Associated with other cop per minerals.

Chrysocolla.

CuSi03.2H20.

Monoclinic. Usually in pris matic crystals.

Characterized by its color and streak.

Vivinnite.

and lepidomelane, p. 409, which may give a light green streak.

NONMETALLIC II. Give a 1. Can be scratched

Cleavage and Fracture.

Color.

Luster.

Hardness.

Spec.

Grav.

Pale brown, green, yellow, white.

Vitreous, pearly.

Usually dark brown, green to black. May be yellow.

Vitreous.

Perfect cleavage in one plane.

The Micas or re lated micaceous minerals, which possess such a perfect cleavage that they can be split into exceed ingly thin sheets. Sometimes they oc cur as aggregates of minute scales when the micaceous structure may not be readily appar-

Yellowish brown, green, white.

Vitreous, pearly.

Black, greenish black.

Adamantine to pearly.

Green of various shades.

Vitreous, pearly.

ent.

White applegreen, gray.

When impure as in soapstone, dark gray, dark green to almost black.

Pearly, greasy.

Very soft. Will leave a mark on cloth.

White, gray green.

Pearly, vitreous.

LUSTER, colorless streak, by the finger nail.

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. In foliated masses; in tabular crystals with hexagonal or diamondshaped outlines: in scales.

The common mica or ising-glass. Characterized by its micaceous structure, its perfect cleavage, the elasticity of its leaves and its light color. While in the mass it may be brown or green, the thin sheets are colorless.

Muscovite

(Potash Mica).

Monoclinic. In irregular foli ated masses. Six-sided tab ular crystals rare.

The common dark green or black mica. Even in thin sheets it shows a smoky color. Sheets are flexible and elastic.

Biotite.

(AI,Fe)(SiO,)s.

Monoclinic. In irregular foli ated masses. Often in sixsided tabular crystals, fre quently large.

Usually a light- though sometimes a dark-colored mica. Often shows a coppery-like reflection from the cleavage surface. Occurs in crys talline limestone.

Phlogopite.

(Al.FeHSiO,),.

Monoclinic. Usually in masses of small irregular scales.

Characterized by its micaceous structure and its shining black color.

Lepidomelane.

(SiO<)3?.

Monoclinic. Usually i n i r- regular foliated masses, at times in compact masses of minute scales.

Characterized by its green color and by the fact that thin sheets are flexible but not elastic.

Clinochlore,

Penninite (Ripidolite, Chlo rite).

H8Mg5Al2Si20i8.

Monoclinic. Foliated or compact.

Characterized by their greasy feel, softness, frequently distinctly foli ated or micaceous structure. Can not be positively toldapart byphysical tests. See p. 296.

Talc

(Steatite,

Soapstone).

Pyrophyllite

Rhombohedral. Commonly foliated massive. At times in broad tabular crystals.

Luster on cleavage surface pearly, elsewhere vitreous. S e c t i 1 e. Transparent to translucent. Can be split with some difficulty into thin sheets which are somewhat flexible but not elastic.

Brucite.

40'J

NONMETALLIC II. Give a 1. Can be scratched

Cleavage and Fracture.

Color.

Luster.

Hardness.

Spec.

Grav.

Perfect pinacoidal C. Two other cleavages not so prominent.

Colorless, white, gray. Sometimes colored by impur ities.

Vitreous.

One perfect C.

Blue, bluish green to colorless.

Pearly to vitreous.

Cubical C.

Colorless or white.

Vitreous.

F. Uneven.

Pearl-gray or col orless. Turns to pale brown on ex posure to light.

Adamantine.

2-3. Highly sectile.

F. Uneven.

Green or yellow.

Adamantine.

2-3. Highly sectile.

F. Uneven.

Pale yellow.

Resinous.

1.5-2. 5.

F. Uneven. Rhombohedral C. Seldom seen.

Colorless or white.

Vitreous.

F. Conchoidal.

C. Prismatic, sel dom seen.

See also kaolinite, bauxite, and greenockite p 417, which on account

Luster.

colorless streak.

by the finger nail.

(Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. In granular masses or cleavable crystal line.

Characterized by its one perfect cleavage, and two others, one giv ing a conchoidal surface and the other a silky surface, and by its softness.

Gypsum

(Alabaster).

CaS04.2H20.

Monoclinic.

See p. 407.

Vivianite.

Isometric.

See p. 413.

Sylvite

Kc1.

Isometric. In irregular masses. Rarely in rude crystals.

Commonly known as horn-silver, because it can be cut with a knife like horn and because in thin plates it is translucent. More common than the other halogen salts of sil ver but to be distinguished from them only by chemical tests.

CERARGYRITE (Horn Silver).

Isometric. In irregular masses. Rarely in rude crys tals.

Like cerargyrite. To be distin guished from it only by chemical teats.

Embolite.

Orthorhombic. Crystallized. Granular. Earthy.

Bums with a blue flame giving a strong odor of sulphur dioxide. Often earthy and impure. See also p. 407.

Sulphur.

S.

Saline crusts.

Rare minerals. Readily soluble in water; cooling and salty tastes. Readily fusible in the candle flame.

SODA NITER. NaNO,.

Usually in thin crusts, silky tufts and delicate acicular crystals.

!Hter.

Kno,.

of their earthy structure may appear to be softer than the finger nail.

NONMETALLIC II. Give a

2. Cannot be scratched by the finger nail,

a. Show a

Cleavage.

Color.

Luster.

Hardness.

Spec.

Grav.

Cleavage in one plane.

See also the miner als of the mica group, p. 409, which may at times be harder than the fin ger nail.

Lilac, grayish, white.

Pearly.

2. 8-2. 9

Pink, gray, white.

Pearly.

Blue, bluish green to colorless.

Pearly to vitreous.

2. 6-2. 7

Colorless or white.

Vitreous to resi nous.

Cubic.

a

Pi

Colorless, white, red, blue.

Vitreous.

Colorless or white.

Vitreous.

o

0 In 3 directions jS at right angles to each other 2 but with vary- g ing degrees of " ease, g

Colorless, white, blue, gray, red.

Vitreous, pearly.

0)

M

t

ea

y In 3 directions not at right angles to each other, giving rhombohedrons.

Colorless, white and variously tinted.

Vitreous.

Colorless, white, pink, etc.

Vitreous, pearly.

LUSTER, colorless streak.

but can be scratched by a cent.

prominent cleavage.

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. In masses o! small irregular scales. Rarely in six-sided prismatic crystals.

Characterized by its lilac color. Always in very small sheets or scales. A rare mineral often asso ciated with colored tourmalines.

Lepidolite (Lithia Mica).

Monoclinic. Usually in ir regular foliated masses.

Folia somewhat brittle. Charac terized by its color. A rare min eral.

Margarite.

H2CaAl4Si20i2.

Monoclinic. Prismatic crys tals, often in stellate groups. At times divergent, fibrous or earthy.

A rare mineral.

Vivianite.

Usually massive with radia ting structure.

Cleavage rarely prominent. See p.

WITHE RITE. BaC03.

Isometric. In granular cleavable masses or in cubic crystals.

Common salt. Characterized by its salty taste. Fusible in the can dle flame. Highly diathermanous. Compare sylvite, below.

Halite

(Common Salt). NaCl.

Isometric. Same as for hal ite. Crystals frequently show octahedral truncations.

A rare mineral closely resembling halite. To be distinguished from it by its more bitter taste and its greater softness (can usually be scratched by the finger nail).

Sylvite.

Kc1.

Orthorhombic. In granular cleavable masses.

Characterized chiefly by its cleav age. If in a form where this does not show it will require chemical tests to determine it.

Anhydrite.

Rhombohedral. In fine- to coarse-grained cleavable masses. When crystallized shows prismatic, rhombo hedral and 8calenohedral forms.

Effervesces readily when a drop of cold acid is placed upon it. Char acterized by its perfect rhombo hedral cleavage and crystal forms. Clear varieties show strong double refraction. Occurs in large masses as limestone and marble. Crystal 'aces may be harder than a cent.

Calcite.

CaC03.

Rhombohedral

See p. 423.

Dolomite.

NONMETALLIC II. Give a

2. Cannot be scratched by the finger nail,

a. Show a

Cleavage and Fracture.

Color.

Luster.

Hardness.

Spec.

Grav.

Colorless, white, blue, yellow, red.

Vitreous, pearly.

In 3 directions giving tabular diamond-shaped cleavage blocks.

Colorless, white, blue, red.

Vitreous, pearly.

Colorless or white. Gray and brown when impure.

Adamantine.

b. Do not show a 1 . A small splinter is a. Readily soluble in water;

F. Conchoidal.

Colorless, white, red.

Vitreous, greasy.

F. Conchoidal.

One good C. sel dom seen.

Colorless or white.

Vitreous.

F. Conchoidal.

Colorless or white.

Vitreous.

See also halite, p. '413, which may exist in forms in which its cleavage is

Luster.

colorless streak.

but can be scratched by a cent.

; prominent cleavage. ( Continued .)

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic. In aggregates of platy crystals or in tabular orthorhombic crystals with rectangular or diamond shaped outlines. Crystal edges frequently beveled by other faces. At times granu lar.

Characterized by its unusual weight for a nonmetallic mineral, its platy structure, cleavage and pearly luster on basal cleavage. At times to be told from celestite and anglesite only getting a green name (test for barium).

Barite,

Barytes.

(Heavy Spar). BaSO,.

Orthorhombic. In granular platy masses or in tabular crystals like those of barite. At times in long prismaticlike crystals with blunt ter minations.

Very similar in appearance to ba rite. Frequently can only be told from barite and anglesite bv get ting a crimson flame color (test for strontium).

Celestite.

Orthorhombic. Usually earthy and impure. At times in small crystals re sembling those of barite and celestite.

Characterized by its weight. Usu- a ly associated with galena as an iteration product in concentric ayers around an unaltered core of talent. Will often need a test for ead for its positive identification.

Anglesite.

'prominent cleavage. fusible in the candle flame, yield a taste.

Orthorhombic. Commonly massive, granular.

A rare mineral. In the candle flame swells, then fuses. Bitter salty taste.

Carnal I ite. MgCl2.KC1.6H20.

Monoclinic. In crusts, often impure. Rarely in prismatic crystals.

A comparatively rare mineral. Tound only in dry countries. In candle flame swells and then fuses, oweetish-alkaline taste.

Borax.

Usually fibrous or massive or in mealy or solid crusts.

Easily fusible with frothing in candie flame. A rare mineral. As stringent taste.

Kalinite (Potash Alum).

KA1 (SO, )s. 12HsO.

obscure, and chalcanthite, p. 406, which may give a nearly colorless streak.

NONMETALLIC II. Give a

2. Cannot be scratched by finger nail,

b. Do not show a 1 . A small splinter is fusible

b. Insoluble in

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Vitreous to greasy.

F. Uneven.

C. In one direc tion, seldom seen.

Colorless or white.

Adamantine.

F. Conchoidal.

Colorless, yellow, orange, brown.

Resinous.

F. Uneven.

7. 0-7. 2

See also vanadinite below.

2. Infusible

Colorless or white. See also bauxite, wavellite and ser pentine below, which may be nearly white.

Vitreous to resi nous.

F. Uneven.

3-3 a

Pearly, dull.

F. Earthy.

Honey-, citron- or orange-yellow.

Adamantine, resi nous, earthy.

F. Uneven.

4. 9-5. 2

Yellow, browm, gray, white.

Dull, earthy.

F. Uneven.

Ruby-red, brown, yellow.

Resinous.

F. Uneven.

Luster.

colorless streak.

but can be scratched by a cent.

prominent cleavage. in the candle flame.

water.

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. Massive.

Characterized by its peculiar trans lucent appearance, like that of par affine. Its fine powder practically disappears when placed in water but is insoluble.

Cryolite.

Na3AlF6.

Orthorhombic. In granular masses; platy crystals often crossing each other to form a lattice-like effect.

W hen fused in the candle flame is slowly reduced showing globules of lead on surface of fragment. Heavy. Effervesces when a drop of cold acid is placed upon it. Associated usually with galena.

Cerussite.

See p. 429.

Mimetite.

which may fuse slightly.

in the candle flame.

Often massive with radiat ing structure.

See p. 427.

Witherite.

Generally clay-like, com pact or mealy.

Often impure. When breathed upon gives an argillaceous odor. Will adhere to a dry tongue. The basis of most clays.

Kaolinite.

H4Al2Si209.

Hexagonal, hemimorphic. Usually in form of powder. Rarely in crystals.

A rare mineral. Characterized by its color and pulverulent form. Often as a coating on sphalerite.

Greenockite.

CdS.

In rounded grains. Also earthy, clay-like.

A rare mineral. Often impure.

Bauxite.

Hexagonal, pyramidal. In slender prisms. Sometimes in cavernous crystals and also in rounded barrel-shaped forms.

Characterized by its color and crystals. Compare mimetite, above and pyromorphite, p. 429.

Vanadinite.

NONMETALLIC II. Give a

2. Cannot be scratched by the finger nail,

b. Do not show a 2. Infusible

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Yellow, green, white, brown.

Vitreous, pearly.

F. Uneven. One C., not prominent.

Olive to blackishgreen, yellow-green, white.

Greasy-, wax-like.

F. Uneven.

Pale to deep green.

Dull to resinous.

F. Uneven.

Some varieties of angle3ite, p. 415, anhydrite, p. 413, and vivianite, p.413, do not show

3. Cannot be scratched by a cent

a. Show a

Cleavage.

Color.

Luster.

Hardness.

Spec.

Grav.

S C. Pinacoidal.

£

0)

a

O

Blue, usually darker at center of crystal. At times white, gray or green.

Vitreous, pearly.

Cleavage in Only.

O

Light blue, green, gray, salmon to clove-brown.

Resinous.

fl

8 C. Pinacoidal.

o

A

White, yellow, brown, red.

Pearly, vitreous.

2. 1-2. 2

Luster.

colorless streak.

but can be scratched by a cent.

prominent cleavage.

in the candle flame. ( Continued .)

Crystallization and Structure.

Remarks.

Name and Composition.

Usually in radiating hemi spherical. globular forms.

Characterized by its structure.

Wavellite.

(Ai.Oh),(Po),

5H20.

Massive. Fibrous.

See p. 431.

Serpentine.

Massive and amorphous, at times as an incrustation with botryoidal or stalactitic sur face; earthy.

A rare mineral. Characterized chiefly by its color.

Genthite

(Garnierite).

Nickel, magnesium silicate.

a distinct cleavage and might be expected to be included in the above group.

but can be scratched by a knife.

prominent cleavage.

Crystallization and Structure.

Remarks.

Name and Composition.

Triclinic. In bladed struc ture with prominent cleavage plane.

Characterized by its color and the fact that it can be scratched by a knife in a direction parallel to length of crystal but not in a direc tion at right angles to this.

Cyanite.

Commonly massive cleavable.

Rare species. Triphyllite is essen tially LiFePOi and lithiophyllite LiMnPO,.

Triphyllite-

Lithiophyllite.

Monoclinic. Commonly in sheaf-like aggregates of crys tals or in flat tabular crys tals.

Characterized by the grouping of its crystals into a radiating sheaf like aggregate and by the pearly luster of the cleavage face.

Stilbite.

Prominent Cleavage in One Plane Only. See also willemite, p. 431

NONMETALLIC II. Give a

3. Cannot be scratched by a cent,

a. Show a

Cleavage.

Color.

Luster.

Hardness.

Spec.

Grav.

C. Basal.

Colorless, white, pale green, yellow, rose.

Pearly, vitreous.

2. 3-2. 4

C. Pinacoidal.

f

White, yellow, red.

Pearly, vitreous.

§ C. Pinacoidal, J2 n often not prominent.

S

O o

.as

White,

colorless.

Vitreous.

2. 4-2. 5

SC. Pinacoidal.

gs

u a

u

Colorless,

w white.

Vitreous.

g x C. Pinacoidal , g seldom seen.

'a

8 Colorless,

Vitreous to resi nous.

C. Pinacoidal.

W

Colorless, white, gray.

Vitreous, pearly.

2. 8-2. 9

C. Pinacoidal, also basal but seldom seen.

Colorless, white, gray.

Vitreous, pearly.

2. 7-2. 8

C. In two di rections.

C. Prismatic.

Colorless,

white.

Vitreous.

Luster.

colorless streak.

but can be scratched by a knife.

'prominent cleavage. ( Continued .)

Crystallization and Structure.

Remarks.

Name and Composition.

Tetragonal. In prismatic crystals with square crosssection. Often resemble a combination of cube and oc tahedron.

Pearly luster on basal plane (cleav age face), vitreous luster on other faces. Prism faces usually verti cally striated. A zeolite found lining cavities in igneous rocks.

APOPHYLLITE. H7 KCa4 (SiOaJs 4*H20.

Monoclinic. Crystals often tabular parallel to cleavage plane (surface of pearly lus ter).

Pearly luster on cleavage face, elsewhere vitreous. A rare zeo lite found lining cavities in igneous rocks.

Heulandite.

Monoclinic. Crystals usu ally like square prisms ter minated by 4 pyramid faces, the latter faces striated. At times in cruciform penetra tion twins.

Characterized by its crystals, see p. 283. A rare zeolite found lining cavities in igneous rocks.

Harmotone.

5H20.

Monoclinic. In crystalline or granular crystalline masses.

Decrepitates violently in the can dle flame. A rare mineral.

Colemanite.

Ca2B60n.5H20.

Usually massive with radi ating structure.

See p. 427.

Withe Rite.

BaC02.

Monoclinic. Usually cleavable massive to fibrous. Also compact. Rarely in tabular crystals.

Associated with crystalline lime stone.

Wollastonite.

Monoclinic. Commonly in close radi ting aggregates of acicular crystals Fibrous

massive.

Characterized by its radiating structure. A rare mineral.

Pectolite.

Orthorhombic. In slender to acicular prismatic crystals terminated by 4 low pyra mid faces. Prism faces ver tically striated. Often in radiating groups.

Characterized chiefly by its struc ture. A zeolite found lining cavi ties in igneous rocks.

Natrolite.

NONMETALLIC II. Give a 3. Cannot be scratched by a cent,

a. Show a

Cleavage.

Color.

Luster. Hardness.

Spec.

Grav.

C. Prismatic making angles of 55° and 125°.

White, green, black.

Vitreous, pearly.

3. 0-3. 3

g.3c. Prismatic '5 o making angles

2 sot 54° and 126°. .a o

Qcc

Gray, clovebrown, green.

Vitreous, pearly.

§C. Prismatic, g rather poor at .9 '2 90° angles.

0) G to

g 03

White, green, black.

Vitreous.

C. Prismatic with nearly 90° angles.

Rose-red, pink, brown.

Vitreous.

u

a

o

&

S

.b

A In 3 directions g not at right angles to each [2 other, giving rhombohedrons.

0)

M

at

G

Colorless, white and variously tinted.

Vitreous.

Colorless, white, pink, etc.

Vitreous, pearly.

LUSTER, colorless streak.

but can be scratched by a knife.

prominent cleavage. ( Continued .)

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. In slender pris matic crystals, showing prom inent cleavage, giving fre quently a b laded appearance. When terminated the crys tals usually show 2 low dome faces. Sometimes fibrous, asbestiform.

Tremolite, CaMg3Si4012, is white, gray, violet; Actinolite, green of various shades; Amphibole or Horn blende, CaMg3Si40i2 with Na2Al2 Si4Oi2 and Mg2Al4Si4b12, is green to black. The group is characterized chiefly by its broad angle cleavage. Found in metamorphic rocks.

Amphibole

Group.

Essentially calcium, magnesium metasil icates.

Orthorhombic. Lamellar or fibrous.

See p. 435.

Anthophyllite. (Mg,Fe) Si03.

Monoclinic. In stout pris matic crystals with rectan- g u 1 a r cross-section. When terminated they usually show more than 2 faces at ends. Often in granular crys talline masses.

Diopside, CaMgSi206, is colorless, white, pale green ; Pyroxene, light to dark green; A u g i t e, CaMgSi2Os with MgAl2SiOe and NaAlSi206, is greenish black to black. Charac terized by the rectangular crosssection of its crystals and the rather poor prismatic cleavage at right angles. Shows at times a basal parting. Found in igneous rocks.

Pyroxene

Group.

Essentially calcium, magnesium metasilcates.

Triclinic. Usually massive, cleavable to compact, in embedded grains; in large rough crystals with rounded edges.

Characterized by its color.

Rhodonite.

Rhombohedral. In granular cleavage masses or crystal lized.

See p. 403.

Calcite.

Rhombohedral. In fine- to coarse-grained cleavable masses. Often in strongly

curved rhombohedral crys tals.

Will not effervesce when a drop of cold hydrochloric acid is placed upon it Characterized by its rhombohedral cleavage, by its rounded rhombohedral crystals and its frequently pink or flesh color. Pearly lu ?ter on curved crystal faces. Occurs in large

masses as dolomite limestone and marble. Frequently associated

with lead and zinc minerals.

Dolomite.

NONMETALLIC II. Give a 3. Cannot be scratched by a cent,

a. Show a

Cleavage.

Color.

Luster.

Hardness.

Spec.

Grav.

White, yellow, gray, brown.

Vitreous.

Light to dark brown.

Vitreous, pearly.

In 3 directions not at right angles to each other, giving rhombohedrons.

Pink, rose- red, dark red, brown.

Vitreous, pearly.

3. 5-4. 5

3. 5-3, 6

Brown, green, blue, pink, white.

Vitreous.

White, yellow, flesh-red.

Vitreous.

In 3 directions at right angles to each other but with varying degrees of ease.

Colorless, white, blue, gray, red.

Vitreous, pearly.

In 3 directions giv ing tabular dia mond-shaped cleav age blocks.

Colorless, white, blue, yellow, red.

Vitreous, pearly.

C. Octahedral.

Colorless, violet, green, yellow, pink. Usually has a fine color.

Vitreous.

C. Perfect in 6 di rections, dodeca hedral.

Yellow, brown, white.

Strongly resinous.

Dodecahedral C., more or less dis tinct.

White, gray, blue, green.

Greasy, vitreous.

Note. — Apatite, p. 429, may show somewhat imperfect cleavage.

Luster.

colorless streak.

but can be scratched by a knife.

prominent cleavage. ( Continued .)

Crystallization and Structure.

Remarks.

Name and Composition.

Rhombohedral . In granu lar cleavable masses.

A rare mineral.

Magnesite.

MgC03.

Rhombohedral. In cleav able masses or in smal rhombohedral crystals.

After being heated in the candle name a fragment is attracted by magnet.

Siderite.

FeC03.

Rhombohedral. In cleav able masses or in small rounded rhombohedral crys tals.

Characterized by its color, cleavage and softness.

Rhodochro-

Site.

Rhombohedral. Usually in botryoidal or honey-combed masses.

See p. 427.

Smithsonite.

ZnC03.

Rhombohedral. In small rhombohedral crystals with nearly cubic angles.

A zeolite found lining cavities in igneous rocks.

Chabazite.

Orthorhombic. In granular cleavable masses.

See p. 413.

Anhydrite.

CaS04.

Orthorhombic. In tabular crystals and lamellar masses.

See p. 415.

Barite,

Barytes (Heavy Spar).

BaS04.

Isometric. In cubic crystals, often in interpenetration twins.

Characterized by its crystals, color and cleavage. The bluish green variety shows fluorescence, i.e. ap pears green by transmitted and blue by reflected light.

Fluorite.

CaF2.

Isometric, tetrahedral. In cleavable masses or small ronnded crystals.

Characterized by its color, luster and cleavage.

Sphalerite.

ZnS.

Isometric. Massive or in embedded grains.

Yequently blue in color. A rocknaking mineral, never associated vith quartz. Usually opaque to ranslucent.

Sodalite.

NONMETALLIC II. Give a 3. Cannot be scratched by a cent,

b. Do not show a

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Colorless,

2 pale green,

yellow.

O

£

Vitreous.

F. Uneven.

White, pale '-g green, blue.

$

o

Vitreous.

F. Uneven. C. prismatic, seldom seen.

.tS White, gray,

oa oj light green, §*.2 darker green o or brown.

§ a

Vitreous to dull.

F. Uneven. C. prismatic, seldom seen.

C Cd

Colorless or (e f white, o o

2%

Vitreous.

F. Uneven.

o-2

(0 M

15 -2 Colorless or e 8 white. m g

M

Vitreous.

F. Uneven.

O

Colorless or white.

u

O

Vitreous to resinous.

F. Uneven.

Co

Co

.2 Colorless or

white.

©

U

Vitreous, pearly.

Pinacoidal C., may be obscure.

2. 7-2. 8

§

Colorless or white.

Vitreous.

Prismatic C., may be obscure.

Brown, green,

P blue, pink,

white.

t-

Cq

Vitreous.

F. Uneven. Rarely shows rhombohedral C.

§ Gray, brown low.

Resinous, ada mantine.

F. Uneven. Pris matic C., seldom prominent.

LUSTER, colorless streak.

but can be scratched by a knife.

prominent cleavage.

Crystallization and Structure.

Remarks.

Name and Composition.

Monoclinic. Usually in crys tals developed with nearly equal dimensions in all di rections and many faces.

Characterized by its luster and crystals. Usually transparent. Occurs with the zeolites, lining cav ities in igneous rocks.

Datolite.

Orthorhombic. Often in ra diating crystal groups. Also stalactitic, mammillary.

Characterized by its structure. Pyroelectric.

Calamine.

Tetragonal. In prismatic

crystals, granular or mas sive.

Often altered.

SCAPOLITE. CajAleSieOjs with

Orthorhombic. Frequently in radiating groups of acicular crystals.

Effervesces in cold acids. Falls to powder in candle flame.

Aragonite.

CaC03.

Isometric. In crystals, usu ally trapezohedrons.

Characterized by its crystals and its glassy luster. A zeolite found lining cavities in igneous rocks.

Analcite.

Orthorhombic. Often in masses with radiating struc ture; granular; rarely in hex agonal pyramidal crystals.

Heavy. When a fragment is placed in cold hydrochloric acid there is a brisk effervescence for a moment and then the action ceases.

Witherite.

In radiating acicular crys tals.

See p. 421.

Pectolite.

Radiating prismatic.

See p. 421.

Natrolite.

Rhombohedral. In rounded botryoidal forms. Often in honey-combed masses.

Harder than most carbonates. A Fragment effervesces when placed in cold hydrochloric acid.

Smithsonite.

Monoclinic. In thin crystals with sharp edges, wedgeshaped.

Characterized by its crystals.

Titanite

(Sphene).

NONMETALLIC II. Give a 3. Cannot be scratched by a cent,

b. Do not show a

Color.

Luster.

C Fracture!1 Hardn.*,

Spec.

Grav.

Yellowish to . reddish § brown.

1?

Resinous, vitre ous.

F. Uneven. Pris matic C., seldom prominent.

p.ti Yellowish to Et -9 reddish £ g brown.

m 6

Resinous.

F. Uneven.

5. 2-5. 3

O 2

& £ White, yelot3 low, green,

g brown.

Vitreous, ada mantine.

F. Uneven.

o. Usually a brilliant

a shade of yel- w 03 low or orange. &T Also red,

£% gray, green.

Vitreous to ada mantine.

F. Uneven.

a "o Colorless,

3 yellow, or- k ange, brown.

"5

Resinous.

F. Uneven.

7. 0-7. 2

w Yellow,

brown, gray, white.

Dull, earthy.

F. Uneven.

White, green, black.

Vitreous.

F. Uneven.

Rather poor pris matic C.f at 90° angles.

0)

Green, blue, violet, brown, colorless.

Co

Vitreous, greasy.

F. Uneven.

Green, brown, yellow, gray.

Resinous.

F. Uneven.

Luster.

colorless streak.

but can be scratched by a knife.

-prominent cleavage. ( Continued. .)

Crystallization and Structure.

Remarks.

Name and Composition.

Tetragonal. In prismatic o pyramidal crystals. Ii rolled grains.

A rare mineral. Heavy.

Xenotime.

ypo4.

Monoclinic. In small crys tals or as rolled grains.

A rare mineral. Heavy.

Monazite.

(Ce.La, often with ThSi04.

Tetragonal. In octahedrallike crystals. Massive, granular.

A rare mineral. Heavy.

Scheelite.

Tetragonal. Usually in very thin square tabular crystals. Less frequently octahedral in habit. Also granular massive.

Characterized by its crystals and color. Heavy.

Wulfenite.

Hexagonal. In small pris matic crystals. Prism faces often curved, giving barrel shapes. In granular masses.

A rare mineral. Heavy. Fuses slowly in candle flame.

Mimetite.

Pb4 (PbCI) CAsOJ,.

See p. 417.

Bauxite.

Monoclinic. In stout rec tangular crystals with rec tangular cross-section.

See p. 423.

Pyroxene

Group.

Essentially calcium and magnesium sili cates.

Hexagonal. In prismatic

crystals, often large, usually with prominent pyramid planes. Also massive.

Characterized by its crystals.

Apatite.

Hexagonal. In small crys tals. Often in rounded barrel shaped forms. Crystals at times cavernous. Often

globular and botryoidal.

characterized chiefly by its structure and color. Heavy.

Py Romor- Phite.

NONMETALLIC II. Give a 3. Cannot be scratched by a cent,

b. Do not show a

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Yellow,

. green, white, ® brown, o

Vitreoua, pearly.

F. Uneven. One C., not prominent.

oS

a Olive to 'g blackish

Js green, yellow- g green, white.

.T5 fl 9

Greasy, waxlike.

F. Uneven.

(53 Y ello w-green , a white, color- a g less, blue,

§ ® gray, brown.

Vitreous.

F. Uneven. May show fairly good

J White, gray, blue, green.

Greasy, vitreous.

F. Conchoidal. Dodecahedral C., seldom seen.

? Deep azure- J blue, green- " ish blue.

Vitreous.

F. Uneven.

NONMETALLIC II. Give a 4. Cannot be scratched by a knife,

a. Show a

Cleavage.

Color.

Luster.

Hardness.

Spec

Grav.

C. Basal.

►

White to pale green or blue.

Vitreous to greasy.

© C. Pinacoidal.

Colorless, white, gray.

Vitreous, pearly.

2. 8-2. 9

Luster.

colorless streak.

but can be scratched by a knife.

; prominent cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Lsually in radiating hemi spherical, globular forms.

Characterized by its structure.

Wavellite.

Massive. Fibrous in the as bestos variety.

Characterized by its massive structure, mottled green color and frequently by the presence of veins of finely fibrous material, known as chrysotile or asbestos.

Serpentine.

H4Mg3Si2Os.

Massive and in disseminated grains.

See p. 439.

Willemite.

Zn2Si04.

Troostite.

Massive or in embedded grains.

See p. 425.

Sodalite.

(Si04),.

Usually massive.

Characterized by its color.

Lazurite (Lapis- Lazuli).

Luster.

colorless streak.

but can be scratched by quartz.

prominent cleavage.

Crystallization and Structure.

Remarks.

Name and Composition.

Usually cleavable to com pact massive.

A rare mineral. Usually found with lepidolite, tourmaline, etc.

Amblygonite.

Lsually cleavable massive to fibrous.

See p. 421.

Wollastonite.

Cleavage in two planes. , Cleavage in one plane only. See also hypersthene and willemite below.

NONMETALLIC II. Give a

4. Cannot be scratched by a knife,

a. Show a prominent

Cleavage.

C. Pinacoidal.

Color.

C. Pinacoidal.

C. Pinacoidal.

C. Basal.

White, gray, pale lavender, yellow ish, greenish.

Grayish white, green, pink.

Hair-brown, gray grayish green.

Yellowish to blackish green to gray.

C. Pinacoidal.

Cleavage in two directions. C. Prismatic.

Luster.

Hardness.

Pearly, vitreous.

Vitreous, pearly.

Vitreous.

Vitreous.

Blue, usually darker at center of crystal. At times gray or green.

Vitreous, pearly.

Colorless, white.

C. Basal and pinacoidal making a 90" angle.

Colorless, white gray, cream, red green.

Vitreous.

Vitreous, pearly.

Spec.

Grav.

LUSTER, colorless streak.

but can be scratched by quartz.

cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic. In thin tab uiar crystals or scales B laded or foliated structure

Pearly luster on cleavage face, else where vitreous. Often associated with corundum, chlorite, margarite, etc.

Diaspore.

Orthorhombic. In prismatic crystals, deeply striated ver tically and seldom distinctly terminated. Also massive, columnar to compact.

Pearly luster on cleavage face, else where vitreous.

Zoisite.

Orthorhombic. Commonly in long slender unterminated crystals. Often in close par allel groups. Fibrous, co lumnar.

In schistose rocks.

Sillimanite

(Fibrolite).

Al2Si06.

Monoclinic. In slender pris matic crystals, striated par allel to length of crystal. Also fibrous, granular.

Characterized by its olive-green color. When transparent shows dichroism ; i.e., in transmitted light appears green in one position and brown in another. In metamorphic rocks; often in crystalline lime stones.

Epidote.

Ca,(Al,OH)

(Al,Fe),(Si04),.

B laded.

See p. 419.

Cyanite.

Al2Si06.

Radiating prismatic.

See p. 421.

Natrolite.

(SiO,)s.2H20.

Monoclinic. In cleavable masses or in irregular grains as a rock constituent. May be in crystals, see Figs. 272— 274, p. 219.

Orthoclase is monoclinic while microcline is triclinic. Ordinarily

they can only be told apart by a microscopic examination. The green amazon stone is usually microcline. Characterized by its 2 cleavage planes at righ angles; the basal cleavage is the better. Found as a prominent constituent of granite rocks and pegmatite veins, associated with quartz and mica.

Orthoclase,

Vlicrocline (Potash Feldspar). KAlSiaO..

NONMETALLIC II. Give a 4. Cannot be scratched by a knife,

a. Show a prominent

Cleavage.

Color.

Luster.

Hardness.

Spec.

Grav.

C. Basal per fect. C. Pinacoidal not so distinct. The two make an gles with each other varying from 86° 50' to 86° 24'.

Colorless, white, gray, greenish, bluish, reddish. Often exhibit a beautiful play of color on the cleav age surfaces.

Vitreous, pearly.

2. 6-2. 7

et>

j§ C. Prismatic.

p.

o

B

.a

White, gray, pink, emerald-green

Vitreous.

to

§ C. Prismatic § making angles C of 55° and 125°.

White to green to black.

Vitreous, pearly.

3. 0-3. 3

C. Prismatic. Perfect at an gles of 54° and 126°.

Gray, clovebrown, green.

Vitreous, pearly.

C. Prismatic. Not very per fect at angles nearly 90°.

Greenish to browniah black.

Vitreous.

C. Prismatic. Rather poor at 90° angles.

White to green to black.

Vitreous.

LUSTER, colorless streak.

but can be scratched by quartz.

cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Tri clinic. In cleavable masses or in irregular grains as a rock constituent. Albite may be in thin tabular crystals or with a curved lamellar structure.

Albite NaAlSi308; Oligoclase 3NaAlSi308 lCaAl2Si208; Andesine lNaAlSi308 lCaAl2Si208; Labradorite =lNaAlSi3083CaAl2Si208; Anorthite CaAl2Si2Og. Charac terized bj a perfect basal cleavage and a pinacoidal cleavage not so distinct; the two making an angle with each other of nearly 90°. Often on the best cleavage surface will be seen a series of fine parallel striation lines due to intimate twining. Often they show a fine play of colors on cleavage surfaces, pale blue in albite and oligoclase; bright blue, green, gold, etc., in an desite and labradorite. Rock con stituents; albite and oligoclase in the light colored granitic rocks; the others in the darker colored, more basic igneous rocks.

Plagioclase

Feldspars.

Combinations in varying amounts of NaAISiaOg, the Al bite molecule, and of CaAl2Si2Og, the An orthite molecule.

Monoclinic. In flattened prismatic crystals, vertically striated; sometimes very large. Also massive, cleav able.

Lilac to pink called kunzite. Green is called hiddenite. Often alters to other minerals with a dull gray color. Not common.

Spodumene.

Monoclinic. In slender pris matic crystals, showing prominent cleavage.

See p. 423.

Amphibole

Group.

Orthorhombic. Commonly lamellar or fibrous massive; fibers often very slender. Also in aggregates of prisms. Distinct crystals rare.

Characterized by its cleavage an gle. Sometimes fibrous (asbestiform. Not common. An ortho rhombic amphibole.

Anthophyllite.

Monoclinic. Long prismatic crystals, vertically striated. Acute terminations charac teristic. Also in groups of acicular crystals. Fibrous.

A rare mineral.

Acmite

Monoclinic. In stout pris matic crystals with rectan gular cross-section.

See p. 423.

Pyroxene

Group.

NONMETALLIC II. Give a

4. Cannot be scratched by a knife,

a. Show a prominent

Cleavage.

Color.

Luster.

Hardness.

Spec.

Grav.

Enstatite has 2 fair prismatic "a C., at 90°. o Hypersthene £ has perfect g pinacoidal C.

Gray-brown, green, bronzebrown, black.

Pearly, bronzelike.

5. 5-6. 5

3. 2-3. 3

bO

S C. Prismatic at nearly 90°.

U

Rose-red, pink, brown.

Vitreous.

C. Basal and pyramidal.

Yellow, brown,

blue, black.

Adamantine.

3. 8-3. 9

Dodecahedral C., seldom seen.

White, gray, blue, green.

Greasy, vitreous.

b. Do not show a

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Colorless or white.

Vitreous.

F. Uneven.

tA-fGray, white.

2 ja colorless.

"5

o:5

Vitreous to dull.

F. Uneven.

m § Colorless, pale a) green, yellow.

' i c

o &

Vitreous.

F. Uneven.

Colorless, white, to pale 8 yellow.

Vitreous.

F. Uneven.

White, gray, light to dark green, brown.

Vitreous to dull.

F. Uneven. Pris matic C., seldom seen.

LUSTER, colorless streak.

but can be scratched by quartz.

cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic . Crystals usually prismatic but rare. Commonly massive, fibrous or lamellar.

Enstatite is light colored; with in crease of iron, bronziio, is olivegreen to brown, often with bronzelike reflections; hypersthene, rich in iron, is dark green to almost black. An orthorhombic pyroxene.

Enstatite

(Bronzite).

Hypersthene.

Triclinic. Usually massive, cleavable to compact.

See p. 423.

Rhodonite.

Tetragonal. In pyramidal crystals. At times tabular with promin nt basal plane.

A rare mineral.

Octahedrite

(Anatase).

Ti02.

Isometric. Massive or in

embedded grains. Rarely in dodecahedral crystals.

Frequently blue. A rock-making mineral, never associated with quartz. Opaque to translucent.

Sodalite.

; prominent cleavage.

Crystallization and Structure.

Remarks.

Name and Composition.

In trapezohedrons.

See p. 427.

Analcite.

Isometric. In trapezohe drons.

Characterized by its crystals. Usually gray in color and with a dull luster. T ranslucent to opaque. Found as phenocrysts in basic igneous rocks, never with quartz.

Leucite.

Ka1

Monoclinic. Usually crys tallized.

See p. 427.

Datolite.

Orthorhombic. In prismatic crystals.

See p. 445.

Danburite.

Tetragonal. Prismatic crys tals, granular or massive.

Often altered. Opaque to translu cent.

Scapolite.

Ca( A l8Si90 a with NajAlaSisOwCl.

NONMETALLIC II. Give a 4. Cannot be scratched by a knife,

b. Do not show a

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Colorless, gray, greenish, reddish.

Greasy, vitreous.

F. Unoven. Pris matic C., seldom seen.

Apple-green, gray, white.

d

Vitreous.

F. Uneven.

Yellow- q green, white, colorless,

k'h blue, gray, brown.

Vitreous.

F. Uneven. May show fairly good

Sj

o a Olive to " a grayish- S d green, brown. M-0

Vitreous.

F. Uneven. C., rarely seen.

cc£*

0) 2 y-,

3 . Green,

O brown, blue,

_aj red, pink, a white, black.

Vitreous.

F. Uneven.

tn

Green,

brown, yel low, blue, red.

Vitreous, resinous.

F. Uneven.

White to green to black.

Vitreous.

F. Uneven. Rather poor pris matic C., at 90° angles.

Clove-brown, gray, green, yellow.

Vitreous.

F. Conchoidal.

Pinacoidal C., not prominent.

LUSTER, colorless streak.

but can be scratched by quartz.

prominent cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Hexagonal. Usually mas

sive. Rarely in small prisms.

A rock-making mineral. Com monly found in igneous rocks which do not contain quartz. Usually opaque to translucent with a greasy luster.

Nephelite.

Orthorhombic. Reniform, globular and stalactitic with crystalline surface. Ingroups of tabular crystals, often bar rel-shaped. Distinct crys tals rare.

Characterized by its structure and pale green color. Translucent.

Prehnite.

H oCa Al2 ( Si04 )s.

Massive and in disseminated grains. Rarely in hexagonal prismatic crystals.

Characterized by its color and granular structure. Associated at Franklin with red zincite and black franklinite. Troostite is brown or gray in color.

Vvillemite.

Zn2Si04

Troostite.

Orthorhombic. Usually

granular either in masses or disseminated.

Characterized usually by its green color, glassy luster and granular structure. Occurs in basic igneous rocks.

Chrysolite

(Olivine, Peridot).

Hexagonal, rhombohedral. Usually in slender prismatic crystals.

See p. 447.

Tourmaline.

A complex boron sil icate containing chiefly Al, Fe, Mg, Mn, alkalies, F and OH.

Tetragonal. In square pris matic crystals terminated usually by base and pyramid. Often columnar. Granular massive.

Usually green or brown in color. Transparent to translucent. Often occurs in crystalline limestones.

Vesuvianite

(Idocrase)

Monoclinic. In stout pris matic crystals with rectan gular cross-section.

Seep 423.

Pyroxene

Group.

Triclinic. Crystals with

acute edges, wedge-shaped. Also lamellar, lamellse often curved.

Characterized by its crystal habit. Transparent to translucent. Not common.

Axinite.

Chiefly various shades of brown.

NONMETALLIC II. Give a 4. Cannot be scratched by a knife,

b. Do not show a

Color. Luster.

Cleavage and Fracture.

Hardness, gee.

Red-brown to

brownish

black.

Resinous, vitreous, dull when altered.

F. Uneven.

Reddish brown, fleshred, olivegreen.

Vitreous, dull when altered.

F. Uneven. C. seldom prominent.

Softer when al tered.

Brown, gray, green, yellow.

Resinous, adaman tine.

F. Uneven. Pris matic C. seldom prominent.

3. 4-3. 5

o

Yellowish to 'o reddish brown.

W

o

Resinous.

F. Uneven.

5. 2-5. 3

" Brown to

m black.

O

Adamantine.

F. Uneven.

a

Reddish brown to black.

0)

a

o

Adamantine.

F. Uneven. C. not prominent.

Hair-brown to black.

Adamantine.

F. Uneven.

Brown to pitchblack.

Pitchy or resinous.

F. Uneven to conchoidal.

3. 5-4. 2

Blue, rarely colorless.

Vitreous.

F. Conchoidal.

C. Pinacoidal not prominent.

Luster.

colorless streak.

but can be scratched by quartz.

prominent cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic. In pris

matic crystals.

See p. 439.

Staurolite.

(AlOJ.fAl.OH)

See p. 437.

Andalusite

(Chiastolite).

Al2SiOs.

Monoclinic. Wedge-shaped crystals.

See p. 427.

Titanite

(Sphene).

Monoclinic. Granular.

A rare mineral. Heavy.

Monazite.

(Ce, La, often with ThSiO..

In irregular masses; in rolled grains.

See p. 447.

Cassiterite.

(Tin Stone) Sn02.

Tetragonal. In prismatic

crystals vertically striated; often slender acicular. Crys tals frequently twinned.

Usually gives a light brown streak. Usually opaque to translucent.

Rutile.

Ti02.

Orthorhombic. Only in crystals. Habit varied; tab ular; prismatic; resembling hexagonal pyramids, etc.

A rare mineral.

Brookite.

Ti02.

Monoclinic. Massive and in embedded grains. Crystals often tabular.

A rare mineral.

Allanite.

R"=Ca and Fe.

R" =Al,Fe,Ce,La Di.

Orthorhombic. In em

bedded grains; also massive compact. In six-sided pris matic crystals.

Transparent to translucent. Mos commonly found altered with foli - ated structure, a grayish greer color, and softer than a knife.

Iolite

(Cordierite).

Blue.

NONMETALLIC II. Give a 4. Cannot be scratched by a knife,

b. Do not show a

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Deep azureblue, greenish blue.

Vitreous.

F. Uneven.

a Azure-blue.

Vitreous.

F. Uneven.

Blue, green, white, gray.

Greasy, vitreous.

F. Conchoidal. Dodecahedral C. seldom seen.

Pink to red. See tourmaline, p. 439.

Black. The following minerals may be almost or quite black; cassiterite,

NONMETALLIC II. Give a 5. Cannot be scratched

a. Show a

Cleavage

Color.

Luster.

Hardness.

Spec.

Grav.

Perfect basal C.

Colorless, yellow, pink, bluish, green ish.

Vitreous.

C. Pinacoidal.

Hair-brown, gray, grayish green.

Vitreous.

C. Prismatic.

White, gray, pink, emerald-green.

Vitreous.

C. Octahedral.

Colorless, yellow, red, blue, gray, black.

Adamantine.

See also corundum, p. 445, which may show a parting resembling cleavage.

LUSTER, colorless streak.

but can be scratched by quartz.

; prominent cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Usually massive.

Characterized by its color.

Lazurite

(Lapis-Lazuli).

Usually in pyramidal crys tals.

A rare mineral. Characterized by its color. Told from Iazurite by its crystals. Opaque.

Lazulite.

Massive.

See p. 437.

Sodalite.

rutile, brookite, allanite, p. 441; pyroxene and tourmaline, p. 439.

LUSTER, colorless streak, by quartz.

prominent cleavage.

Crystallization and Structure.

Remarks.

Name and Composition.

Orthorhombic. In prismatic crystals, terminated by base, pyramids and domes. Also coarse to fine granular.

Characterized by its crystals, hard ness and cleavage.

Topaz.

(OH) iso. with F.

Orthorhombic. Commonly in long slender crystals.

Seep. 433.

Sillimanite

(Fibrolite).

Al2Si05.

Monoclinic.

See p. 435.

Spodumene.

Isometric. In octahedral

crystals, faces usually rough and curved. In irregular

rounded pieces.

Characterized by its extreme hard ness. Rare.

Diamond.

Chiefly light to dark green. i Chiefly colorless or white.

See also jadeite, p. 447.

NONMETALLIC II. Give a 5. Cannot be scratched

b. Do not show a

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Colorless,

white,

smoky, ame thyst. Vari ously colored when impure.

Vitreous, greasy.

F. Conchoidal

O.

U .

° Colorless, w white to pale

yellow.

Is

Vitreous.

F. Uneven.

.jj co White, color- q less.

Vitreous.

F. Conchoidal.

White, gray, blue, yellow, brown, green, pink, red.

Adamantine to vitreous.

F. Uneven.

Lavender, blue, green, brown, red,

black.

Q

O

Vitreous.

F. Conchoidal.

3. 5-3. 8

Bluish green,

h green, yellow,

pink, colorless,

o

a

Vitreous.

F. Conchoidal, uneven.

° Yellowish to emeraldgreen.

Vitreous.

F. Conchoidal, uneven. C. nol

prominent.

3. 6-3. 8

LUSTER, colorless streak, by quartz.

'prominent cleavage.

Crystallization and Structure.

Remarks.

Name and Composition.

Rhombohedral, trapezohedral. Irregular massive; in embedded grains; as pebbles, sand. Crystals usually show hexagonal prism terminated by what appears to be a hex agonal pyramid. Prism faces are striated horizon tally. Crystals frequently tapering.

Characterized by its crystals; its conchoidal fracture and vitreous luster. For description of varieties see pp. 188-190. Transparent to translucent. Most common min eral.

Quartz.

Si02.

Orthorhombic. In prismatic crystals, resembling those of topaz. Also disseminated in indistinct crystals and irreg ular masses.

Characterized by its crystals. Distinguished from topaz by its lack of cleavage. Transparent to translucent. A rare mineral.

Danburite.

Rhombohedral. In small rhombohedral crystals.

A rare mineral.

Phenacite.

Be2Si04.

Hexagonal, rhombohedral. In irregular masses showing at times an almost cubic structure owing to a rhombo hedral parting. In rude prisms, often barrel-shaped.

Characterized by its extreme hard ness. Ruby=red; sapphire blue; various other colors. Emery is im pure corundum usually with magne tite. May show rhombohedral

parting with nearly 90° angles.

Corundum.

A1203.

Isometric. In octahedrons; sometimes twinned.

Characterized by its crystals and its hardness. Ruby spinel when red.

Spinel.

Hexagonal. Usually in pris matic crystals with basal plane; pyramid faces rare. Sometimes deeply furrowed vertically. Crystals at times large. Also irregular, mas sive.

Often shows a mottling of color due to alternation of transparent and opaque spots. Crystals very char acteristic. Most common color blue-green, known as aqua-marine; also deep green as emerald; yellow as golden beryl; pink as morganite. Found in pegmatite veins.

Beryl.

Orthorhombic. In tabular crystals which are frequently twinned giving hexagonal shapes.

A rare mineral. Characterized by its hardness.

Chrysoberyl

(Alexandrite).

NONMETALLIC II. Give a 5. Cannot be scratched

b. Do not show a

Color.

Luster. .

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Green,

brown, blue, os red, pink,

35 white, black, d

ts

©

a

u

a

tL

. a

Vitreous.

p. Uneven.

g.b

K N

00 Green, gray,

.12 white.

a .a "3

£t3

Vitreous.

F. Splintery. C., prismatic at nearly 90° angles, not prominent.

.jS s Olive to gray J2 ish green, t£? brown. -

Vitreous.

F. Uneven. C. rarely seen.

' 6.5-7

'J9 -2 -

.2 Green,

-§ brown, yel- g low, blue,

O red.

Vitreous, resinous.

F. Uneven.

o3 - - -

$ Dark green.

Vitreous.

F. Conchoidal, uneven.

Reddish brown to black.

g

o

U

.O

Adamantine.

F. Uneven. C. not prominent.

Jj Reddish

O brown, desh red, olivegreen.

Vitreous, dull when altered.

F. Uneven. C. seldom prominent

LUSTER, colorless streak.

by quartz.

prominent cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Rhombohedral. Usually in slender prismatic crystals, striated vertically. Crosssection usually resembles a spherical triangle. When terminated usually shows base and rhombohedrons. Often in slender radiating crystals.

Widely various in color. Most com monly black. Of the lighter colors green is most frequent. Character ized by its crystal structure. Crystals exhibit pyro-electricity; i.e., after being heated they will attract and hold small pieces of tis sue paper, etc., A candle flame may be used. Found in pegmatite veins and metamorphic rocks.

Tourmaline.

A complex boron sil icate containing chiefly Al,Fe,Mg, Mn, alkalies F and (OH).

Always massive, usually closely compact.

Translucent. A rare mineral.

Jadeite

(Jade).

Orthorhombic. Usually granular.

See p. 439.

Chrysolite

(Olivine, Peridot).

Tetragonal.

See p. 139.

Vesuvianite (I doc rase).

Isometric. Usually in octa hedrons. Sometimes

twinned.

Characterized by its crystals and hardness. A variety of spinel; see p. 445.

Gahnite (Zinc Spinel). ZnAl204.

Tetragonal. In irregular

masses; in compact fibrous, reniform structure; in rolled grains. Rarely in prismatic crystals, twins.

Very heavy. Usually opaque to translucent. Often gives a lightbrown streak. Usually to be scratched by quartz with difficulty. Occurs as rolled grains in sand, in pegmatite veins and in granite rocks.

Cassiterite

(Tin Stone).

Sn02.

Orthorhombic. In coarse prismatic crystals with nearly square cross-section.

Often soft on surface due to altera tion. Frequently a cross-section of a crystal will show a dark-colored cross due to a regular arrangement of impurities in the interior of crys tal. Occurs in metamorphic rocks, usually clay slates.

Andalusite

(Chiastolite).

Al2Si05.

Chiefly various shades of . See also vesuvianite, p. 447.

NONMETALLIC II. Give a 5. Cannot be scratched

b. Do not show a

Color.

Luster.

Cleavage and Fracture.

Hardness.

Spec.

Grav.

Clove-brown, green, yellow, gray.

Vitreous.

F. Conchoidal.

C. Pinacoidal, not prominent.

Red-brown to brownish g black.

£3

Resinous, vitreous. Dull when altered.

F. Uneven.

° 2

g-g Brown, red, d.s gray, green, j5 £ colorless.

" 8 a

Adamantine.

F. Conchoidal.

C. prismatic not prominent.

Is

a d Usually S brown to red.

Also various o shades of yel-

3 low, green,

° pink, etc.

Vitreous.

F. Uneven.

6. 5-7. 5

Yellow minerals, see corundum, beryl, p. 445, axinite and garnet above.

Pink to red minerals, see corundum, spinel, beryl, p. 445, tourmaline, p. 447, and garnet above.

Black mineral, see tourmaline, p. 447.

LUSTER, colorless streak, by quartz.

'prominent cleavage. (Continued.)

Crystallization and Structure.

Remarks.

Name and Composition.

Triclinic.

See p. 439.

Axinite.

Orthorhombic. In prismatic crystals; very commonly in cruciform penetration twins.

Characterized by its crystals. May be altered to earthy material in which case it can be softer than a knife. Opaque to translucent. Occurs in mica schist.

Staurolite.

Tetragonal. Usually in small prisms terminated by pyramid of the same order. As rolled grains in sand.

Characterized by its crystals. Usually opaque.

Zircon.

Isometric. Commonly as

dodecahedrons trapezohedrons or a combination of the two. In rolled grains.

usu ally light yellow or green. Pyrope deep red. Almandite brown to red. Spessartite red. Andradite green, yellow, brown, to black. Uvarovite emer ald-green. Characterized by crys tal shape and commonly its red color. An accessory rock mineral. Commonly in metamorphic rocks. As sand.

Garnet.

R" Ca,Mg,Fe,Mn R'" Al.Fe.Cr.

Index To Determinative Tables

Acmite, 435 Actinolite, 423 Alabandite, 397 Albite, 435 Allanite, 441 Amblygonite, 431 Amphibole, 423, 435 Analcite, 427, 437 Anatase, 437 Andalusite, 441, 447 Andesine, 435 Anglesite, 415 Anhydrite, 413, 425 Anorthite, 435 Anthophyllite, 423,

Antimony, 391 Apatite, 429 Apophyllite, 421 Aragonite, 427 Argentite, 389 Arsenic, 391 Arsenopyrite, 399 Atacamite, 407 Augite, 423 Axinite, 439, 449 Azurite, 407

Barite, 415, 425 Bauxite, 417, 429 Beryl, 445 Biotite, 409 Bismuth, 397 Bismut finite, 391 Borax, 415 Bomite, 393 Bournonite, 391 Brochantite, 407 Bronzite, 437

Brookite, 441 Brucite, 409

Calamine, 427 Calaverite, 393 Calcite, 413, 423 Carnallite, 415 Cassiterite, 405, 441,

Celestite, 415 Cerargyrite, 411 Cerussite, 417 Chabazite, 425 Chalcanthite, 407 Chalcocite, 389 Chalcopyrite, 393 Chloanthite, 399 Chromite, 395, 401 Chrysoberyl, 445 Chrysocolla, 407 Chrysolite, 439 Cinnabar, 387, 397,

Clinochlore, 409 Cobaltite, 399 Colemanite, 421 Columbite, 401 Copper, 397 Corundum, 445 Covellite, 393 Crocoite, 405 Cryolite, 417 Cuprite, 395, 403 Cyanite, 419, 433

Danburite, 437, 445 Datolite, 427, 437 Diamond, 443 Diaspore, 433

Diopside, 423 Dolomite, 413, 423

Embolite, 411 Enargite, 389 Enstatite, 437 Epidote, 433

Fluorite, 425 Franklinite, 401

Gahnite, 447 Galena, 387, 391 Garnet, 449 Garnierite, 419 Genthite, 419 Gersdorffite, 399 Goethite, 397, 403,

Gold, 397 Graphite, 387 Greenockite, 417 Gypsum, 411

Halite, 413 Harmotone, 421 Hematite, 387, 395, 401, 403 Heulandite, 421 Hornblende, 423 Hypersthene, 437

Ilmenite, 401 Iolite, 441

Jadeite, 447 Jamesonite, 389

Kalinite, 405 Kaolinite, 417

Index

Labradorite, 435 Lazulite, 443 Lazurite, 431, 443 Lepidolite, 413 Lepidomelane, 409 Leucite, 437 Limonite, 387, 397, 403, 405 Linnseite, 399 Lithiophyllite, 419

Magnetite, 399 Magnesite, 425 Malachite, 407 Manganite, 395 Marcasite, 399 Margarite, 413 Microcline, 433 Millerite, 393 Mimetite, 417, 429 Molybdenite, 387 Monazite, 429, 441 Muscovite, 409

Natrolite, 421, 427,

Nephelite, 439 Niccolite, 393, 399 Niter, 411

Octahedrite, 437 Oligoclase, 435 Olivenite, 407 Olivine, 439, 447 Orpiment, 407 Orthoclase, 433

Pectolite, 421, 427 Penninite, 409 Pentlandite, 393 Phenacite, 445 Phlogopite, 409

Platinum, 397 Plagiocla.se Feldspars,

Polybasite, 389 Prehnite, 439 Proustite, 403 Psilomelane, 389, 401 Pyrargyrite, 395, 403 Pyrite, 399 Pyrolusite, 387, 389 Pyromorphite, 429 Pyrophyllite, 409 Pyrrhotite, 393 Pyroxene, 423, 429, 435, 439

Quartz, 445

Realgar, 405 Rhodochrosite, 425 Rhodonite, 423, 437 Rutile, 405, 441

Scapolite, 427, 437 Scheelite, 429 Serpentine, 419, 431 Siderite, 425 Sillimanite, 433, 443 Silver, 397 Smalltite, 399 Smithsonite, 425, 427 Sodalite, 425, 436, 437, 443 Soda Niter, 411 Sphalerite, 395, 405,

Spinel, 445 Spodumene, 435, 443 Stannite, 391 Staurolite, 441, 449 Stephanite, 389 Stibnite, 387, 391

Stilbite, 419 Stromeyerite, 389 Sulphur, 407, 411 Sylvanite, 393 Sylvite, 411, 413

Talc, 409 Tantalite, 401 Tellurium, 391 Tetrahedrite, 389 Thorite, 405 Titanite, 427, 441 Topaz, 443 Tourmaline, 439, 447 Tremolite, 423 Triphyllite, 419 Turgite, 395, 401,

Uraninite, 401

Vanadinite, 417 Vesuvianite, 439, 447 Vivianite, 407, 411,

Wavellite, 419, 431 Willemite, 431, 439 Witherite, 413, 417, 421, 427

Wolframite, 395, 401,

Wollastonite, 421,

Wulfenite, 429

Xenotime, 429

Zincite, 405 Zircon, 449 Zoisite, 433

Appendix I.

List Of Minerals Suitable For A Small Mineral Collection.

For the convenience of those who desire to possess a small but representative mineral collection the following list is given. The names of the more important species are printed in black face type, and the names of other desirable but less important minerals in ordinary type. The first list includes 59 names, while the complete list numbers 109.

Graphite

Sulphur

Gold in quartz

Silver

Copper

Orpiment

Stibnite

Molybdenite

Galena

Argentite

Chalcocite

Sphalerite

Cinnabar

Millerite

Niccolite

Pyrrhotite

Bornite

Chalcopyrite

Pyrite

Marcasite

Arsenopyrite

Tetrahedrite

Halite

Fluorite

Cryolite

Quartz (several varieties)

Opal

Cuprite

Zincite

Corundum

Hematite

Spinel

Magnetite

Franklinite

Chromite

Cassiterite

Rutile

Pyrolusite

Manganite

Limonite

Brucite

Calcite

Dolomite

Siderite

Rhodochrosite

Smithsonite

Aragonite

Witherite

Strontianite

Cerussite

Malachite

Azurite

Orthoclase

Albite

Oligoclase

Labradorite

Leucite

Pyroxenes (several varieties) Spodumene Pectolite Rhodonite Amphibole (sev eral varieties) Beryl Garnet Chrysolite Willemite Seapolite Vesuvianite Zircon Topaz Andalusite Cyanite Datolite

Epidote

Prehnite

Calamine

Tourmaline

Staurolite

Apophyllite

Heulandite

Stilbite

Chabazite

Analcite

Natrolite

Muscovite

Lepidolite

Biotite

Phlogopite

Clinochlore

Serpentine

Talc

Kaolinite

Chrysocolla

Titanite

Columbite

Monazite

Apatite

Pyromorphite

Mimetite

Vanadinite

Turquois

Uraninite

Barite

Celestite

Anglesite

Anhydrite

Wolframite

Scheelite

Wulfenite

Appendix Ii. Mineral Statistics

Introduction

Brief statistics relative to the amount and value of the pro duction of the different economic minerals and metals are pre sented below. The figures have been taken from the bulletins of the United States Geological Survey entitled Mineral Resources of the United States for 1925 and 1927 (Preliminary Summary). Unless otherwise stated all statistics refer to productions from the United States.

Summary Of The Mineral Production Of The United States For 1925

Metals

Pig Iron . $739,316,333

Silver . 45,911,864

Gold . 49,860,200

Copper . 237,832,000

Lead . 113,956,000

Zinc . $84,456,000

Mercury . 762,616

Aluminum 36,430,000

Total . $1,380,280,000*

Nonmetals

Bituminous Coal

Anthracite Coal . Natural Gas

Petroleum .

Clay Products . .

Cement .

Lime .

This figure

$1,060,402,000 Sand (Molding,

etc.) . $103,706,038

327,664,512 Slate . 12,575,326

265,271,000 Stone . 174,216,792

1,284,960,000 Borates . 3,085,660

423,446,917 Gypsum . 47,577,240

281,075,691 Phosphate Rock 11,545,678

42,609,141 Pyrite . 650,448

includes various metals not listed separately.

Appendix

Nonmetals ( Continued )

Sulphur . $29,000,000 Glass Sand

Salt . 26,162,361 Graphite .

*Mineral Paints . 28,310,631 Mica .

Native Asphalt . 4,148,400 Quartz .

Bauxite . 1,988,250 Talc .

Feldspar . 1,315,654 Tungsten Ores .

$3,836,085

96,361

205,376

2,011,793

Total . $1,232, 420, 000f

Total value of all mineral products $5,677,630,000 (including mineral fuels).

Aluminum

The production of bauxite, the ore of aluminum, in 1927 had a value of $1,988,780. The largest production was in 1918, value $3,447,992. The value of the metal produced from ore in 1927 was $39,266,000.

Antimony

Only a small amount of antimony ore is mined in the United States. The domestic source of the metal is largely confined to the smelting of antimonial lead ores where it is obtained in the nature of a by-product. 1,972 tons of metallic antimony came from this source in 1925. The value of metal and ore imported in 1925 was $2,560,504.

Apatite, see Phosphate Rock

Arsenic

Arsenic, chiefly in the form of the oxide, is produced by only a few companies in the United States and the total production is comparatively small. It is practically all obtained as a by-product from the smelting of ores that contain small amounts of the metal. A large part of the production comes from the smelting of the cop per ores at Butte, Montana, which contain arsenic in the form of the mineral enargite and from lead ores in Utah. The amount of arsenic oxide, or white arsenic, sold in 1925 was 11,317 tons with a value of $1,199,247.

Zinc and lead pigments, t Exclusive of mineral fuels.

Appendix

Asbestos

The amount of asbestos produced is small, amounting to $336,882 worth in 1927. Imports for the same year had a value of $8, 150,340.

Barite

The value of the barite produced in 1927 was $1,594,423. The largest amount came from Missouri.

Bauxite, see Aluminum Bismuth

The bismuth produced in the United States is derived from the refining of tin and lead and the amount so produced is small. Imports of the metal reached the value of $100,773 in 1927.

Borax

A considerable amount of the borates produced in the United States comes from the mineral colemanite. All the borates mined are grouped together, however, under the title borax. The value of the production for 1927 was $3,473,399.

Calcite

Following are the statistics for the production of Portland Ce ment for 1927.

Quantity in Barrels

Value of Shipments

43,732,278

6,180,255

14,580,654

7,017,047

6,778,384

13,965,241

10,775,375

5,415,144

$66,711,069

9,939,412

26,623,396

11,312,783

Ip 117,047

20,858,202

16,380,090

9,124,405

8,853,869

5,655,835

7,564,863

4,430,439

38,257,129

14,242,901

10,232,908

10,615,428

6,580,732

19 other states .

65,116,274

Total .

173,206,513

$278,854,647

Total production of cement of all classes for 1915 had a value of $74,285,248; for 1925 of $288,661,096.

Appendix

The value of the sales of limestone for the year 1925 follows:

Florida .

. . . . $4,348,234

Ohio .

. . $9,617,437

Illinois .

. . . . 7,686,005

Pennsylvania. . .

. . 13,630,050

Indiana .

. . . . 18,140,974

Virginia .

. . 2,611,157

Michigan .

. . . . 6,327,634

West Virginia. . .

. . 2,998,579

Missouri .

. . . . 4,082,920

Wisconsin .

. . 2,079,512

New York .

. . . 10,149,440

Other states

. . 16,336,086

Total .

. . $98,008,028

Cement, see above Chromite

The production and imports of chromite for the year 1926 follow. The domestic production was very small, the total value being $2,079. Imported, chiefly from New Caledonia, British South Africa, Portuguese Africa, Canada, Cuba, Greece and India, 215,464 tons; value $1,704,947.

Clay

The total value of the various kinds of clay sold in 1927 was $13,075,520. The value of kaolin produced was $3,650,000. The value of kaolin imported during 1927 was $2,937,113. The total value of all brick and tile products for 1926 was $313,935,186; that of pottery products was $116,493,308.

Copper

The amounts of copper produced in the years 1910, 1920 and 1927 follow:

Alaska .

Pounds

4,311,026

Pounds

66,093,924

Pounds

56,489,214

Arizona .

297,250,538

552,988,731

681,168,117

California .

45,760,200

11,822,028

25,802,603

Colorado .

9,307,497

4,282,616

8,006,801

Idaho .

6,877,515

1,922,116

1,811,103

Michigan .

221,462,984

153,483,952

195,135,199

Montana .

283,078,473

177,743,747

225,208,853

118,298,342

Nevada .

64,494,640

55,580,322

New Mexico .

3,784,609

52,159,751

79,761,222

Tennessee .

16,691,777

16,727,803

14,498,951

Utah .

125,185,455

110,357,748

267,705,597

Other states .

1,954,795

5,898,302

10,154,981

Total .

1,080,159,509

1,209,061,040

1,684,040,983

Appendix 457

Note. Practically the entire production of Michigan is from native copper; that of the other states is from various other ores.

The value of copper varies quite widely from year to year. One pound was worth about 16.75 c. in 1900; 15.63 c. in 1905; 13 c. in 1910; 17.47 c. in 1915; 18.4 c. in 1920; 13.1 c. in 1927. 1

The United States furnished in 1925 about two thirds of the total world's production. Statistics are not available for subse quent years. Other countries that produce notable amounts of copper are Mexico, Spain, Japan, Australia, Chile, Peru, Canada, Germany, Belgium Congo.

Corundum

The production of corundum for abrasive purposes is practi cally negligible. Since 1898, when the production was valued at $275,064, it has rapidly fallen until in 1927 the only corundum produced was in the form of emery with a total value for the year of $5,855. Considerable amounts of emery are imported, the value for 1927 being $264,613. The decline in the domestic pro duction of corundum is due in large part to the manufacture of the artificial abrasives, carborundum and alundum. The value of such materials produced in 1925 was $7,988,930. For the pro duction of corundum as sapphire, see under gem stones.

Feldspar

The amount of feldspar sold in 1925 was as follows:

Quantity

Value

California .

Tons

6,524

26,514

39,028

8,386

62,137

42,227

$133,284

497,348

757,339

96,129

804,741

729,004

Maine .

New Jersey .

New York .

Tennessee .

Undistributed .

T otal .

184,816

$3,017,845

Appendix

Fluorite, Fluorspar

The value of shipments of fluorite during 1925 was as follows: Colorado, $153,707; Illinois, $1,024,516; Kentucky, $833,794; and New Mexico, $40,325.

Garnet

The value of garnet produced for an abrasive during 1925 was $712,853.

Gem Stones

The value of the gems and ornamental stones produced in the United States for 1915 was $170,431. More than 20 different minerals contributed to this total, the majority of them being found in small amounts, however. The values of the production of the more important stones follow: Sapphire, $88,214; Tourma line, $10,969; Turquoise and turquoise matrix, $11,691. The production has since declined until in 1923 the estimated value was only $65,000.

Gold

The values of the gold production in the years 1910, 1915 and 1927 are given below.

Alaska .

$16,126,749

$16,710,000

$5,918,300

Arizona .

3,149,366

4,555.900

4,198,200

California .

19,715,440

22,547,400

11,679,200

Colorado .

20,507,058

22,530,800

5,356,300

Idaho .

1,096,842

1,170,600

314,400

Montana .

3,730,486

4,978.300

1,159,200

Nevada .

18,878,864

11,883,700

3,089,300

Oregon .

679,488

1,867,100

298,200

South Dakota .

Utah

5,402,257

7.403.500 3,907,900

3.480.500

6.670.400

4.124.400

Other states .

5,647,228

2,610,700

Total .

$94,933,778

$101,035,700

$45,418,600

Appendix

The gold production of the leading countries for the year 1925 follows :

United States . $49,860,200 Japan

Canada . 35,880,800 China

Mexico . 16,309,900 India .

Russia and Siberia . 21,931,800 Australasia

Africa . 218,497,300

Total including all other countries

$6,557,800

2,218,100

8,140,700

13,914,600

$395,968,000

Graphite

The sales of natural graphite in 1927 was valued at $232,971. Artificial graphite produced in 1927 amounted to 12,257,239 pounds.

Imports of graphite in 1927, chiefly from Ceylon, Madagascar and Mexico amounted to $723,923 in value.

Gypsum

The value of the gypsum produced in the various states for 1925

follows:

Iowa .

Kansas .

Michigan .

Nevada .

New York .

. . . . $6,734,271 . . . . 1,009,510

. . . . 5,447,294

. . . . 1,721,809

. . . 16,219,906

Ohio .

Oklahoma .

Texas .

Other states. . .

. . . $6,394,132 . . . 2,599,463

. . . 3,721,954 . . . 3,728,901

Total .

. . . $47,577,240

Appendix

Iron

The production in long tons of the different iron ores by states is given in the following table for 1925.

Hematite

Limonite

Magnetite

Alabama .

6,453,875

14,490,529

36,856,244

639,375

202,942

172,959

125,803

952,623

15,731

1,039

58,160

4,470

96,272

Tp.nnessee .

106,557

265,322

Utah .

817,149

541,283

Other states .

85,284

17,677

Total .

59,546,690

884,600

1,472,004

Total of all ores 61,907,997 tons.

Production of Lake Superior District by ranges in long tons.

Marquette

Menominee

Gogebic

Vermilion

Mesabi*

1,384,010

524,735

227,075

1,430,862

690,435

119,590

2,863,848

2,274,192

2,914,081

891,910

2,839,350

1,982,080

1,794,970

2,625,475

1,027,103

3,945,068

3,680,738

3,104,033

1,675,949

8,158,450

3,772,645

4,472,630

3,344,551

1,578,626

20,156,566

4,631,427

4,983,729

4,746,818

1,390,360

30,576,409

3,817,892

4,665,465

4,996,237

1,541,645

30,802,409

4,457,609

5,651,542

8,298,206

1,053,518

36,641,880

Total to

3,813,687

5,009,022

6,377,710

1,331,753

34,851,109

end of

154,513,781

146,967,986

153,110,258

50,109,069

710,636,346

The Mesabi District first shipped ore in 1892.

Total for Lake Superior District to end of 1925 1,231,660,414 tons.

Appendix

Kaolin, see Clay- Lead

The production of lead in 1925 follows:

Short Tons

Colorado .

Idaho . 123,363

Missouri . 208,547

Montana . 22,008

Oklahoma . 7g 437

utah . 166*844

Other states . 55,347

Total . 686,451

The average price of lead for 1925 was 8.7 cents per pound.

Limestone, see Calcite Magnesite

The production of magnesite for 1927 amounted to 121,490 tons, valued at $1,090,550. California and Washington were the pro ducing states. The imports of the mineral were valued at $954,935.

Manganese

The United States produces only small amounts of rich mangan ese ores. The output comes chiefly from Arizona, Arkansas, Idaho, Montana, etc. Lower grade ores come f rom Colorado and Georgia. A larger amount of manganiferous ores, in which the manganese is saved as a by-product, is produced. These ores are chiefly found in Michigan, Minnesota, and Wisconsin. The value of all ores in 1927 was $5,096,299.

Mercury

The production of mercury (quicksilver) for 1925 was as follows:

California, 7,614 flasks (75 lbs. each); value, $632,936 Texas, Nevada, Arizona, and Idaho, 1,560

flasks; value, 129,680

Appendix

The value of mercury imported for consumption in the United States for 1925 was valued at $1,200,878. It came chiefly from Italy and Spain.

Mica

The total value of the mica produced during 1927 was $322,621. Importations during the same year were valued at $1,630,309.

Nickel

No nickel ores are known to have been mined in the United States in recent years. Some nickel is obtained as a by-product in the electrolytic refining of copper. The value of the nickel ore and matte imported during 1927 was $8,801,960.

Phosphate Rock

The production of phosphate rock during 1925 was as follows:

Value

Florida . $8,789,070

Tennessee . 2,429,059

Other states . 327,549

Total . $11,545,678

Platinum

The amount of the platinum produced in the United States is small , being about 8000 ounces in 1 927. The value of the platinum metals imported during 1927 was $12,413,494. Russia produced 200,450 ounces in 1905, 275,000 ounces in 1910, and 124,000 ounces in 1915, 20,000 ounces in 1921 and 25,000 ounces in 1924. Colom bia produced 46,000 ounces in 1924. Other sources at present are negligible. The value of importations into the United States of unmanufactured and manufactured platinum, except jewelry, in 1927 amounted to $23,601,425. The price of platinum has been steadily rising. The value of refined platinum ranged during 1925 from $117 to $120 an ounce,

Appendix

Potash Salts

The value of potash salts produced in the United States in 1927 was $2,448,146. The value of the various salts imported during 1927 was $18,369,805.

Pyrite

The production of pyrite for 1927 was 215,786 long tons having a value of $80.4,006. The important producing states are California, Virginia and New York.

Quartz

Pure crystalline quartz, used for pottery, scouring soaps, paints, etc., averaged in 1927 about $6.70 per ton in its crude form. The total production of quartz for these purposes, and including that used as a flux or for abrading purposes for 1925, had a value of $3,419,806. The value of the sandstone production in the United States for the same year was $10,920,016. Sand, used for glass, moulding, building, etc., was produced from a great number of states, the chief being Pennsylvania, Ohio, New York, Illinois, New Jersey, Indiana and Michigan and had a total value in 1925' of $107,542,123.

Rutile, see Titanium

Salt

The production of salt in the different important states for 1925 follows:

Quantity

Value

California .

Short Tons

277,010

244,310

841,970

384,190

287,020

86,100

25,870

88,700

$1,351,327

1,719,347

6,512,752

3,121.631

3,220,936

424,035

180,053

520,660

Kansas .

Michigan .

New York .

Ohio .

Utah .

West Virginia .

Other states .

Total .

2,235,170

$17,050,741

Appendix

Silver

The amounts and values of the silver production for the years 1905, 1915 and 1925 are given below:

Ounces

Commer cial Value

Ounces

Commer cial Value

Ounces

Commer cial Value

2,605,700

12.942.800 8,125,600

13,454,700

5.863.500

10.319.800

2.789.500

$1,589,477

7,895,108

4,956,616

8,207,367

3,576,735

6,295,078

1,701,595

5,665,672

7,199.745

13,042,466

14,423,173

14,453,085

13,073,471

7,103,463

$2,826,500

3,591,900

6.506.800 7,195,600 7,210,500 6,522,200

3.543.800

7,371,358

4,434,890

7,663,437

12,596,609

6,846,806

21,240,515

6,001,809

$5,115,722

3,077,814

5,318,425

8,742,047

4,751,683

14,740,917

4,165,256

Colorado .

Idaho .

Montana .

Utah .

Other states . .

56,101,600

$34,221,976

74,961,075

$37,397,300

66,155,424

$45,911,864

The commercial value of silver varies quite widely from year to year. An ounce was valued in 1900 at 61.6 c., in 1905 at 60.4 c., in 1910 at 49.3 c., and in 1915 at 51.9 c. From 1918 to June, 1923, it was valued at one dollar per ounce as provided by the Pittman act. The average value in 1925 was 69.4 c.

Soapstone, see Talc Sulphur

The value of the sulphur produced in 1927, chiefly from Iouisiana and Texas was approximately $38,300,000. The value of the ex ports for the same year was $16,798,600.

Talc and Soapstone

The production of talc and soapstone for 1925 follows:

New Jersey and Penn- Vermont . $533,603

sylvania . $90,502 Other states . 393,775

New York . 993,913 -

Total

$2,011,793

Appendix

Tin

The domestic production of tin is negligible. The value of the imports of the metal for 1927 was $100,865,205.

Titanium

Very little rutile is produced in the United States. The locali ties in Nelson County, Virginia, are no longer productive. Con centrates of both rutile and ilmenite have been recently obtained from beach sands of Florida.

Tourmaline, see Gem Stones

Tungsten

The total value of tungsten concentrates produced during 1927 was $724,000. These come chiefly from California and Colorado.

Turquoise, see Gem Stones

Zinc

The production of zinc in the United States for 1925 is given below:

Short Tons

Colorado . 30,811

Kansas . 118,778

Missouri . 14,794

Montana . 57,658

New Jersey . 89,261

Other states . 399,545

Total . 710,847

The world's production of spelter by countries for 1925 follows:

Metric Tons

Belgium . 170,860

France and Spain . 79,378

Germany . 62,494

Poland . 114,424

Great Britain . 38,671

United States . 519,765

Other countries . 144,408

Total . 1,130,000

Index

h ote. Names of mineral species are printed in heavy-faced tvpe; synonyms and variety names in italics; general matter in light-faced type.

A

Accessory rock-making minerals

Acicular structure, 64 Acid potassium sulphate, 101

Acini te, 248

Actinolite, 252 Adamantine luster, 73 Adularia, 236

Algirite, 248 /Enigmatite, 255

Agalmatolite, 298 Agate, 189

Alabandite, 155

Alabaster, 321

Albite, 240

Alexandrite, 206

Allanite, 275

Almandite, 259 Altaite, 152 Aluminum, tests for, 104 Aluminum minerals, 326 Amalgam, 142 Amazon stone, 238 Amblygonite, 308 Amethyst, 188 Ammonium carbonate, 102 Ammonium hydroxide, 102 Ammonium molybdate, 102 Ammonium oxalate, 102 Ammonium sulphocyanite, 102 Amorphous minerals, 379 Amphibole, 252 Amphibole Group, 252

Analcite, 285 Anatase, 209 Andalusite, 271 Andesine, 242 Andesite, 349 Andradite, 259 Anglesite, 318 Anhydrite,. 319 Ankerite, 223 Annabergite, 309 Anorthite, 243 Anthophyllite, 252 Antimony, 134 Antimony minerals, 328 Antimony, tests for, 104 Apatite, 304 Apatite Group, 304 Apophyllite, 281 Aquamarine, 256 Aragonite, 228 Aragonite Group, 227 Arfvedsonite, 254 Argentite, 149 Arkose, 352 Arsenic, 133 Arsenic minerals, 328 Arsenic, tests for, 105 Arsenopyrite, 168 Asbestos, 295 Asterism, 75 Atacamite, 185 Augite, 246 Aurichalcite, 233 Aventurine, 188 Axinite, 275 Azurite, 233

Index

B

Balas ruby, 201 Banded structure, 65

Barite, 315

Barite Group, 315 Barium chloride, 102 Barium hydroxide, 102 Barium minerals, 329 Barium, tests for, 106 Barytes, 315 Basalt, 349 Bauxite, 215 Bead tests, 99 Beam balance, 71 Beryl, 255 Biotite, 290 Bismuth, 135 Bismuthinite, 147 Bismuth minerals, 329 Bismuth, tests for, 106 Black-band ore, 225 Black jack, 153 Blowpipe, 88 Blowpipe flame, 90 Blue vitriol, 322 Bog-iron ore, 213 Boracite, 312 Borax, 313 Borax, 101 Bornite, 160 Boron, tests for, 107 Bort, 127

Botryoidal structure, 65

Bouiangerite, 172 Bournonite, 172

Brachy-axis, 52 Brachydome, 53 Brachypinacoid, 54

Braunite, 206

Brazilian emerald, 279 Brittle, 68

Brochantite, 320 Bromyrite, 182

Bronzite, 245

Brookite, 209

Brown hematite, 213

Brucite, 216

Cadmium minerals, 330 Cairngorm stone, 188

Calamine, 277 Calaverite, 170 Calcite, 217 Calcite Group, 217 Calcium, tests for, 107 Cancrinite, 258 Capillary pyrites, 158 Capillary structure, 64 Carbonado, 127 Carbon, tests for, 108 Carborundum, 196 Carbuncle, 262 Carnallite, 186 Cornelian, 189 Cassiterite, 206 Cat's eye, 188, 206 Celestite, 317 Cerargyrite, 181 Cerussite, 231 Chabazite, 284 Chalcanthite, 322 Chalcedony, 189 Chalcocite, 152 Chalcopyrite, 161 Chalcotrichite, 192 Chalk, 218, 352 Chalybite, 224 Chemical formula, 82 Chemical groups, 81 Chessylite, 233 Chiastolite, 271 Chloanthite, 165 Chlorine, tests for, 108 Chlorite Group, 293 Chlorophane, 183 Chlorospinel, 201 Chondrodite, 276

Index

Chromite, 204

Chromium minerals, 330 Chromium, tests for, 108

Chrysoberyl, 205 Chrysocolla, 299 Chrysolite, 262

Chrysoprase, 189 Chrysotile, 295

Cinnabar, 156

Cinnamon sto7ie, 260 Classification of minerals, 124 Clay ironsto?ie, 225 Cleavage, 3, 66 Clino-axis, 56 Clinochlore, 293 Clinodome, 59 Clinohumite, 276 Clinopinacoid, 59 Clintonite Group, 292 Closed tube test, 96 Coatings on charcoal, 94 Cobalt bloom, 309 Cobaltite, 166 Cobalt minerals, 331 Cobalt nitrate, 102 Cobalt, tests for, 108 Cogwheel ore, 172 Colemanite, 312 Colloidal minerals, 87 Coloradorite, 156 Color of minerals, 74 Columbite, 300 Columnar structure, 64 Compact structure, 65 Concentric structure, 65 Conchoidal fracture, 67 Conglomerate, 351 Constancy of interfacial angles, 7 Contact metamorphic minerals,

Copper, 140

Copper glance, 152 Copper minerals, 331 Copper 7iickel, 158 Copper pyrites, 161

Copper, tests for, 109 Cordierite, 257 Corundum, 194 Covellite, 157 Crocidolite, 254 Crocoite, 320 Cryolite, 184 Crystal combinations, 16 Crystal, defined, 1 Crystal distortion, 17 Crystal form, 15 Crystal habit, 16 Crystallized structure, 64 Crystallographic axes, 19 Cube, 21 Cuprite, 192 Cyanite, 272 Cymophane, 206

D

Dacite, 349 Danburite, 269 Datolite, 272

Deltoid dodecahedron, 33 Demantoid, 262 Dendritic structure, 64 Desmine, 283

Determinative Mineralogy, 380 Determinative Tables, 385

Diamond, 126 Diaspore, 211 Dimorphism, 87 Diopside, 246 Dioptase, 265 Diorite, 348 Diploid, 29

Divergent structure, 64 Dodecahedron, 22 Dolerite, 348 Dolomite, 222 Double refraction, 78 Drusy structure, 64 Dry-bone ore, 226 Dry reagents, 101 D unite, 348

Index

E

Earthy structure, 65 Eloeolite, 257 Elastic, 69

Electric calamine, 278 Electrum, 136 Elements, 125 Elements, list of, 103

Embolite, 182

Emerald, 256 Emery, 195

Enargite, 177 Endlichite, 308

Enstatite, 245 Epidote, 274 Erubescite, 161 Erythrite, 309 Essonite, 260 Eucryptite, 249

F

Fahlore, 174

Famatinite, 177 Fayalite, 263

Feather ore, 171 Feldspar Group, 235 Felsite, 349

Fergusonite, 302

Fibrolite, 271 Fibrous fracture, 67 Fibrous structure, 64 Filiform structure, 64 Flame tests, 98 Flexible, 69 Flint, 189 Flosferri, 229 Fluorine, tests for, 109 Fluorite, 182 Fluorspar, 182 Foliated structure, 65 Fosterite, 263 Fracture, 67 Franklinite, 203 Fusion, 90

G

Gabbro, 348

Gadolinite, 273 Gahnite, 202 Galena, 150 Galenite, 150 Gangue minerals, 367 Garnet, 259 Garnierite, 295 Gay Lussite, 234 Gel minerals, 87 Genthite, 295 Geocronite, 172 Geode, 65 Gersdorfflte, 166 Geyserite, 191 Gibbsite, 216 Glauberite, 315 Glaucophane, 254 Globular structure, 65 Gmelinite, 285 Gneiss, 354 Goethite, 212 Gold, 136 Golden beryl, 256 Gold minerals, 334 Gold, tests for, 110 Goniometers, 8 Gossan, 165 Granite, 347 Granular structure, 65 Graphite, 130 Gray copper, 174 Graywacke, 352 Greasy luster, 73 Greenockite, 157 Grossularite, 259 Groundmass, 350 Gypsum, 320

H

Hackly fracture, 67

Halite, 178

Hardness of minerals, 67

Index

Harmotone, 283 Hausmannite, 206 Hauynite, 258

Heavy spar, 315

Hedenbergite, 246 Hematite, 196

Hemimorphite, 278

Hessite, 152 Heulandite, 282

Hexahedron, 21 Hexagonal axes, 41 Hexagonal minerals, 373 Hexagonal prisms, 43 Hexagonal pyramids, 44, 45 Hexagonal symmetry, 42 Hexagonal system, 41 Hexakistetrahedron, 34 Hexoctahedron, 26 Hiddenite, 249 Hornblende, 252 Hornblendite, 349 Horn silver, 181 Horseflesh ore, 161 Hiibnerite, 323 Humite, 276 Hyacinth, 269 Hyalite, 191 Hyalophane, 237 Hy dr argillite, 216 Hydrochloric acid, 101 Hydrogen sodium phosphate,

Hydrohematite, 211

Hydromagnesite, 234 Hydrozincite, 234 Hypersthene, 245

Ice, 193

Iceland spar, 218 Igneous rocks, 345

Hmenite, 199 Uvaite, 276

Index of refraction, 75

Indices, 15 Indicolite, 280 Infusorial earth, 191

Iodyrite, 182 Iolite, 257

Iridescence, 74 Iridium, 144 Iridosmine, 144 Iron, 143

Iron minerals, 334 Iron pyrites, 163 Iron, tests for, 111 Irregular fracture, 67 Isometric angles, 35 Isometric axes, 19 Isometric minerals, 370 Isometric symmetry, 20 Isometric system, 19 Isomorphism, 84 Isomorphous groups, 86

J

Jacinth, 269

Jadeite, 249 Jamesonite, 171

Jargon, 269 Jasper, 189 Jeffersonite, 246 Jolly balance, 70

K

Kainite, 181 Kalinite, 323

Kaolin, 297

Kaolinite, 297

Kidney ore, 197

Krennerite, 171

Kunzite, 249

Labradorite, 243

Lamellar structure, 65 Lapis-lazuli, 258

Index

Laumontite, 284 Lazulite, 309 Lazurite, 258 Lead, 142

Lead minerals, 335 Lead, tests for, 112

Lepidolite, 290 Lepidomelane, 292 Leucite, 244

Lievrite, 276 Limestone, 218, 352

Limonite, 213 Linnasite, 161 Lithiophilite, 303

Lithium, test for, 112 Litmus paper, 101 Lodestone, 202 Luster, 72

M

Macro-axis, 52 Macrodome, 53 Macropinacoid, 54

Magnesite, 223

Magnesium, tests for, 112 Magnetic pyrites, 159

Magnetite, 202 Malachite, 232

Malleable, 69 Mammillary structure, 65 Manganese minerals, 336 Manganese, tests for, 113

Manganite, 213 Manganotantalite, 300 Marble, 218, 355

Marcasite, 167 Margarite, 292 Marialite, 265, 266 Marl, 353

Massive minerals, 379 Massive structure, 66 Meionite, 265, 266 Melaconite, 193

Melanite, 261

Menaccanite, 199 Meneghinite, 172

Mercury, 142

Mercury minerals, 338 Mercury, tests for, 113

Metacinnabarite, 156

Metallic luster, 73 Metamorphic rocks, 353 Mica Group, 287 Mica-schist, 354 Micaceous structure, 65 Microcline, 237 Microcosmic salt, 101 Microlite, 302 Milky quartz, 188 Millerite, 158 Mimetite, 307 Mispickel, 168 Mizzonite, 265, 266 Molybdenite, 148 Molybdenum minerals, 338 Molybdenum, tests for, 114 Monazite, 302 Monoclinic axes, 56 Monoclinic minerals, 377 Monoclinie prism, 58 Monoclinic pyramid, 58 Monoclinic symmetry, 58 Monoclinic system, 56 Monticellite, 263 Moonstone, 236, 241 Morganite, 256 Muriatic acid, 101 Muscovite, 288

N

Nagyagite, 171 Natrolite, 286 Nephelite, 257 Niccolite, 158

Nickel bloom, 309 Nickel minerals, 339 Nickel, tests for, 114 Niobium, tests for, 114

Index

Niter, 312

Nitric acid, 102 Nonmetallic luster, 73

Noselite, 258

Obsidian, 350

Octahedrite, 209

Octahedron, 21

Oligoclase, 241 Olivenite, 309 Olivine, 262 Onofrite, 156

Onyx, 189 Oolite, 352 Opal, 190 Opalescence, 74 Open tube test, 95 Orpiment, 145 Ortho-axis, 56 Orthoclase, 235 Orthodome, 58 Orthopinacoid, 59 Orthorhombic axes, 51 Orthorhombic minerals, 375 Orthorhombic prism, 53 Orthorhombic pyramid, 53 Orthorhombic symmetry, 53 Orthorhombic system, 51 Oxidizing flame, 92 Oxygen, tests for, 115

P

Palladium, 144

Parameters, 13 Parting, 66 Peacock ore, 161 Pearl spar, 222 Pearly luster, 73 Pectolite, 250 Pegmatite dike, 361 Penninite, 293 Pentagonal dodecahedron, 28

Pentlandite, 155

Percentage composition, 83 Peridot, 262 Peridotite, 348 Perlite, 350

Perovskite, 300 Petalite, 234 Petzite, 152 Phenacite, 265

Phenocryst, 350

Phillipsite, 283 Phlogopite, 291

Phonolite, 349 Phosgenite, 232 Phosphorescence, 75 Phosphorite, 305 Phosphorus, tests for, 115 Picotite, 201 Pitch blende, 313 Pitchstone, 350 Plagioclase feldspars, 238 Plagionite, 172 Plaster of Paris tablets, use of,

Platinum, 142

Platinum minerals, 339 Platinum, tests for, 116 Play of colors, 74 Pleonaste, 201 Plumose structure, 65 Plutonic rocks, 347, 348 Pneumatolytic minerals, 364 Polarized light, 79 Polianite, 211 Pollucite, 245 Polybasite, 176 Polyhalite, 181 Porphyry, 350 Potash alum, 323 Potash feldspar, 235 Potassium iodide and sulphur mixture, 101

Potassium ferricyanide, 102 Potassium ferrocyanide 102 Potassium, tests for, 116

Index

Prehnite, 276

Primary vein minerals, 368

Proustite, 173 Pseudomorphs, 18 Psilomelane, 217 Pumice, 350 Purple copper ore, 160 Pyrargyrite, 173 Pyrite, 163 Pyritohedral class, 28 Pyritohedron, 28 Pyrochlore, 302 Pyroelectricity, 79 Pyrolusite, 210 Pyromorphite, 306 Pyrope, 259 Pyrophyllite, 298 Pyroxene, 246 Pyroxene Group, 245 Pyroxenite, 349 Pyrrhotite, 159

Q

Quartz, 186

Quartzite, 354 Quicksilver, see Mercury

R

Radiated structure, 64 Realgar, 144 Red copper ore, 192 Reducing flame, 92 Refraction of light, 75 Reniform structure, 65 Replacement deposits, 366 Resinous luster, 73 Reticulated structure, 64 Rhodochrosite, 225 Rhodolite, 261 Rhodonite, 251 Rhombohedral class, 46 Rhombohedral minerals, 373 Rhombohedron, 47

Rhyolite, 349 Riebeckite, 254

Rock crystal, 188

Rock-making minerals, 355

Rock salt, 178

Rose beryl, 256

Rose quartz, 188

Rubellite, 280

Rubicelle, 201

Ruby, 195

Ruby copper, 192

Ruby silvers, 173

Rutile, 208

S

Salt, 178

Salt of phosphorus, 101 Samarskite, 302 Sandstone, 351 Sanidine, 236 Sapphire, 195 Satin spar, 321 Scalenohedron, 49 Scale of fusibility, 91 Scale of hardness, 68 Scapolite Group, 265 Scheelite, 324 Schefferite, 246 Schist, 354 Scolecite, 287 Scorodite, 310 Secondary enrichment, 368 Secondary vein minerals, 368 Sectile, 69

Sedimentary rocks, 350 Selenite, 320

Serpentine, 294

Shale, 352

Siderite, 224

Silicon, tests for, 116 Silky luster, 73

Sillimanite, 271 Silver, 139

Silver glance, 149

Index

Silver minerals, 340 Silver nitrate, 102 Silver, tests for, 118 Slate, 354

Smaltite, 165 Smithsonite, 226 Smoky quartz, 188 Soapstone, 296 Soda-feldspar, 240 Sodalite, 258 Soda niter, 311 Sodium carbonate, 101 Sodium, tests for, 118 Spathic iron, 224 Specific gravity, 69 Specular hematite, 197 Sperrylite, 166 Spessartite, 259 Sphalerite, 153 Sphene, 299 Sphenoid, 39 Sphenoidal class, 39 Spinel, 200 Spinel Group, 200 Spodumene, 248 Stalactitic structure, 65 Stannite, 163 Staurolite, 280 Steatite, 296 Stellated structure, 65 Stephanite, 175 Stibnite, 146 Stilbite, 283 Stromeyerite, 153 Strontianite, 230 Strontium, tests for, 119 Structure of minerals, 64 Sublimates in closed tube, 97 Sublimates in open tube, 96 Sublimates on charcoal, 94 Sublimates on Plaster of Paris tablets, 94

Submetallic luster, 73 Sulphides, 144

Sulphur, 132

Sulphuric acid, 102 Sulphur, tests for, 119 Syenite, 347 Sylvanite, 169 Sylvite, 180 Symmetry, 10 Symmetry axis, 10 Symmetry center, 10 Symmetry plane, 10

T

Tabular structure, 65 Talc, 296 Tantalite, 300 Tarnish, 75 Tellurium, 133 Tellurium, tests for, 120 Tenacity of minerals, 68 Tennantite, 174 Tenorite, 193 Tephroite, 263 Test papers, 101 Tetragonal axes, 35 Tetragonal combinations, 39 Tetragonal minerals, 372 Tetragonal prisms, 36 Tetragonal pyramids, 37, 38 Tetragonal system, 35 Tetragonal symmetry, 36 Tetragonal trisoctahedron, 24 Tetrahedral class, 31 Tetrahedrite, 174 Tetrahedron, 32 Tetrahexahedron, 23 Thomsonite, 287 Thorite, 269 Thulite, 274 Tiemannite, 156 Tiger's eye, 188 Tin minerals, 342 Tin stone, 206 Tin, tests for, 121 Titanic iron ore, 199 Titanite, 299

Index

Titanium minerals, 342 Titanium, tests for, 121 Topaz, 270 Tourmaline, 278 Trachyte, 349 Trapezohedral class, 51 Trapezohedron, 24 Travertine, 206, 220, 353 Tremolite, 252 Triclinic axes, 61 Triclinic domes, 62 Triclinic minerals, 378 Triclinic pinacoids, 62 Triclinic prisms, 62 Triclinic pyramids, 62 Triclinic symmetry, 61 Triclinic system, 61 Trigonal trisoctahedron, 25 Trimorphism, 87 Triphylite, 303 Tripolite, 191

Tri-rhombohedral class, 50 Trisoctahedron, 25 Tristetrahedron, 33 Trona, 234 Troostite, 264 Tungsten minerals, 343 Tungsten, tests for, 122 Turgite, 211 Turmeric paper, 101 Turquois, 310 Twin crystals, 18

U

Uneven fracture, 67 Uralian emeralds, 262

Uraninite, 313

Uranium, tests for, 122 Uvarovite, 259

Vanadinite, 307

Vanadium minerals, 343

Vanadium, tests for, 122 Variegated copper ore, 161 Veins and vein minerals, 364 Verd antique marble, 294 Vesuvianite, 266 Vitreous luster, 73 Vitrophyre, 350 Vivianite, 309 Volcanic rocks, 349, 350

W

Water, tests for, 110

Wavellite, 310 Wernerite, 265 Wet reagents, 101 White iron pyrites, 167

Willemite, 264 Witherite, 229 Wolframite, 323 Wollastonite, 250 Wulfenite, 325 Wurtzite, 160

Xenotime, 302

X-Ray evidence of crystal struc ture, 5

Y

Yellow copper ore, 161

Z

Zeolites, 283 Zinc blende,, 153

Zincite, 193

Zinc minerals, 344 Zinc, tests for, 123

Zinkenite, 172 Zircon, 268 Zoisite, 273

Zonal relations of Isometric Forms, 27

Qe 372 ,D2 1929

§ : 010101 000

T 63 0009492 1

Trent University

Qe372 .D2 1929

Dana, James Dwight, 1813-1895 Dana's manual of mineralogy