# 1911 Encyclopædia Britannica/Mineralogy

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​MINERALOGY, the science which describes and classifies the different kinds of mineral matter constituting the material of the earth’s crust and of those extra-terrestrial bodies called meteorites. The study of minerals is thus a branch of natural history, but one in which certain of the exact sciences find an application. The determination of the composition and constitution of minerals is a chemical problem; their optical and other physical properties are determined according to the principles of physics; the study of their crystalline form and structure belongs to crystallography; their modes of occurrence, origins, associations and changes come within the province of geology and petrology; while a consideration of the localities at which they are found requires some acquaintance with geography. Finally, there is the economic side, dealing with the mining and application of useful minerals, the extraction of metals from their ores, and the uses of minerals for building, decoration and jewelry.
In this article we shall treat only of the general characters of minerals; their special characters will be found in the articles on the individual minerals.
After a brief historical sketch the subject will be treated under the following headings:—
| I. | Characters of Minerals. | Characters of Minerals. | Characters of Minerals. | Characters of Minerals. | Characters of Minerals. |
| | | 1. | Morphological Characters. | Morphological Characters. | Morphological Characters. |
| | | | | a. | Crystalline Form. |
| | | | | b. | State of Aggregation: Structure. |
| | | 2. | Physical Characters. | Physical Characters. | Physical Characters. |
| | | | | a. | Optical Characters (Colour, &c.). |
| | | | | b. | Magnetic, Electrical and Thermal Characters. |
| | | | | c. | Characters depending on Cohesion (Hardness, &c.). |
| | | | | d. | Specific Gravity. |
| | | | | e. | Touch, Taste and Smell. |
| | | 3. | Chemical Characters. | Chemical Characters. | Chemical Characters. |
| | | | | Synthesis of Minerals. | Synthesis of Minerals. |
| II. | Occurrence and Origin of Minerals. | Occurrence and Origin of Minerals. | Occurrence and Origin of Minerals. | Occurrence and Origin of Minerals. | Occurrence and Origin of Minerals. |
| | | Alteration of Minerals: Pseudomorphs. | Alteration of Minerals: Pseudomorphs. | Alteration of Minerals: Pseudomorphs. | Alteration of Minerals: Pseudomorphs. |
| III. | Nomenclature and Classification of Minerals. | Nomenclature and Classification of Minerals. | Nomenclature and Classification of Minerals. | Nomenclature and Classification of Minerals. | Nomenclature and Classification of Minerals. |
History.—Owing to their numerous applications for useful and decorative purposes, minerals have attracted the attention of mankind from the earliest times. The stone and bronze implements of prehistoric man and many of his personal ornaments and charms were directly or indirectly of mineral origin. The oldest existing treatise on minerals is that written about 315 B.C. by Theophrastus (περί τῶν λίθον—On Stones, English version by John Hill, 1746), of which only a portion is now in existence. Minerals were then classed as metals, stones and earths. The last five books of Pliny’s Historia naturalis, written about A.D. 77, treat of metals, ores, stones and gems. Some of the Arabian philosophers devoted themselves to the study of minerals, and about 1262 Albertus Magnus wrote his De mineralibus. In the 16th century Georgius Agricola published several large volumes, dealing more especially with the mining and metallurgy of metalliferous minerals, in which more exact descriptions were given of the external characters: he mentioned several minerals by names (e.g. blende, fluor, quartz) which are now in common use. About the same period there appeared the systematic treatise on minerals of K. Gesner (1565), and that on precious stones by Anselm Boethius de Boodt (1609). The remarkable researches of Erasmus Bartholinus on Iceland-spar were published in 1669, and J. F. Henckel’s Pyritologia in 1725. Later came the Systema naturae of C. Linnaeus (1735). Although the importance of chemical properties was recognized by the Swedish chemists—J. G. Wallerius (1747) and A. F. Cronstedt (1758)—the external characters of minerals formed the basis of the mixed systems of classification of A. G. Werner (1774) and of other authors, and even as late as the Natural History System of Mineralogy of F. Mohs (1820).
It was not until the end of the 18th and beginning of the 19th century, when the foundations of crystallography were laid by Romé de l’Isle and R. J. Haüy, and chemistry had assumed its modern phase, that any real advance was made in scientific mineralogy. It was then recognized that chemical composition and crystalline form were characters of the first importance, and that external (natural history) characters were often more or less accidental. During this period numerous mineral substances were analysed by Scheele, Klaproth, Charles Hatchett, Vauquelin, Kirwan, Berzelius, Rose and other chemists, and many new mineral-species and chemical elements discovered. After W. H. Wollaston’s invention of the reflecting goniometer in 1809, exact measurements of the crystalline forms of many minerals were made. The principles of isomorphism and dimorphism enunciated by E. Mitscherlich in 1819 and 1821 respectively cleared up many difficulties encountered in the definition of mineral-species. About the same time also the discovery by E. L. Malus of the polarization of light gave an impetus to the optical examination, by Sir David Brewster and others, of natural crystals. Later, the investigation of rocks in thin section under the microscope led to the exact determination, particularly by A. Des Cloizeaux (1867), of the optical constants of rock-forming minerals.
For a detailed account of the history of mineralogy (including crystallography), see F. von Kobell, Geschichte der Mineralogie von 1650–1860 (München, 1864). The recent history of mineral-species may be well traced in the six editions of J. D. Dana’s System of Mineralogy (1837–1892).
I.—Characters of Minerals.
A distinction is to be made between essential and non-essential characters. Essential characters are those relating to chemical composition, crystalline form, crystallo-physical properties and specific gravity; these are identical, or vary only within certain defined limits, in all specimens of the same mineral-species. Non-essential characters—such as colour, lustre, hardness, form and structure of aggregates—depend largely on the presence of impurities, or on the state of aggregation of imperfectly formed crystalline individuals. In an absolutely pure and perfectly developed crystal all the characters may be said to be essential, but such crystals are of exceptional occurrence in nature, and certain of the characters are subject to modification under different conditions of growth. For example: a well-formed crystal of haematite (“specular iron ore”), with its smooth black faces and brilliant metallic lustre, is strikingly different in appearance from a piece of massive haematite (“red iron ore”), which is dull and earthy and bright red in colour; the former is so hard that it can only with difficulty be scratched with a knife, while the latter is quite soft and soils the fingers. Both specimens will, however, be found on analysis to have the same chemical composition (Fe$_2$O$_3$), the same crystalline structure (as determined by the optical characters under the microscope in the case of the massive variety), and very nearly the same specific gravity (especially if this be determined upon finely powdered material, the effect of cavities being thus eliminated). The essential characters being identical, the difference between the two specimens lies in the state of aggregation of the material: with “specular iron ore” we have a single crystal, while with the “red iron ore” we are dealing with a confused aggregate of minute crystalline individuals, which have interfered with each other’s growth to such an extent that no crystal-faces have been developed. Such differences do ​not therefore depend on the nature of the material, but only on the conditions which prevailed during its growth. (See e.g. Quartz and Calcite.)
In the following enumeration of the more salient characters of minerals it is to be noted that many of the terms used for non-essential characters are purely descriptive and have no exact definition; on the other hand, essential characters can be expressed numerically and are therefore perfectly definite.
1. Morphological Characters.
a. Crystalline Form.—This most important character of minerals can, of course, be determined only when the material available is in the form of crystals (i.e. crystallized), which is not always the case. Massive aggregates of crystalline material are of much more frequent occurrence; when small fragments or thin sections of such material are transparent, the crystalline symmetry may be determined, within certain limits, by the help of the optical characters (see below). External crystalline form must not, however, be considered alone apart from all other characters, for crystals of substances quite different chemically, e.g. silver iodide, zinc oxide and zinc sulphide, are sometimes almost identical in crystalline form; further, in groups of isomorphously related minerals the degree of symmetry will usually be the same and the angles vary only slightly, and unless the crystals are perfectly developed and suitable for exact goniometric measurement no crystallographic distinction can be made between two such species.
All the six systems of crystals and most of the thirty-two symmetry-classes are represented amongst minerals (see Crystallography). Crystals of the same mineral-species may differ very widely in general form or habit; e.g. crystals of Calcite (q.v.) may be rhombohedral, prismatic, scalenohedral or tabular in habit. Other descriptive terms of the habit of crystals are pyramidal, acicular or needle-shaped (from the Lat. acicula, a needle), capillary or hair-like (from the Lat. capillus, hair), &c.; and these peculiarities of habit may sometimes be characteristic of certain minerals. Sometimes also there are characteristic kinds of groupings of crystals: thus parallel, divergent or radiating (e.g. scolecite), rosette-shaped (e.g. haematite—Eisenrosen), reticulated (e.g. rutile), or matted. The faces of natural crystals may be smooth, rough, striated, curved or drusy, i.e. studded with small crystal faces and angles.
b. State of Aggregation: Structure.—According to the particular state of aggregation of a number of imperfectly developed crystals, which have grown together, various kinds of structure may be presented even by the same mineral species. The descriptive terms applied to these structures are almost self-explanatory: thus the structure may be granular (e.g. marble), fibrous (asbestos), radio-fibrous or stellated (wavellite), columnar (beryl), laminar or lamellar (talc), bladed (cyanite), &c., according to the relative shape and sizes of the individual crystals composing the aggregate. When the constituent crystals are invisible to the unaided eye the material is described as compact; incoherent aggregates are powdery or earthy. Minerals which are really amorphous, i.e. without any crystalline structure, are comparatively few in number (e.g. opal); many which are apparently amorphous are really microcrystalline (e.g. turquoise). The term massive is often used loosely for a crystalline mineral not showing crystal-faces. Crystal-aggregates often assume more or less accidental and imitative external forms to which the following descriptive terms are applied: dendritic or arborescent (e.g. copper, pyrolusite), mossy (copper), leafy (gold), wiry or filiform (silver), capillary (millerite), coralloidal (aragonite), globular (aragonite, with concentric structure; wavellite, with radiated structure), mamillary or with breast-like protuberances (arsenic), nodular (malachite), warty (menilite), botryoidal or resembling a bunch of grapes (from βότρυς, a bunch of grapes) (dolomite), reniform or kidney-shaped (menilite), amygdaloidal or almond-shaped (agate), stalactitic (calcite, chalcedony), &c.
2. Physical Characters.
a. Optical Characters.—The action of crystallized matter on transmitted light is a character of the highest importance in mineralogy. Even when the substance is opaque in large masses, it may be sufficiently transparent when in small splinters or in thin sections for the determination of the optical characters. The refractive indices, strength of the double refraction, optic axial angle, extinction angles on certain faces, &c., are characters capable of exact measurement and numerical expression, and are constant for each mineral-species. (See Crystallography.)
In their “diaphaneity,” or degree of transparency, minerals differ very widely even in the same species. Some, such as metals and most metallic sulphides are always opaque; while others may vary in different specimens from perfect transparency to perfect opacity (in the latter case, however, minute fragments will, as a rule, still be transparent). A good example of this is afforded by the varieties of quartz: rock-crystal is water-clear, chalcedony is translucent, and jasper opaque.
The “colour” of minerals is the character which first arrests attention; but being a character which may vary almost indefinitely in one and the same kind of mineral, it affords a typical example of a non-essential character. Thus, fluor-spar and quartz, when in well-formed and 'chemically pure crystals, are quite colourless and transparent; but it would be easy to collect a series of each of these minerals in which almost every shade of colour is represented. Crystals of fluor-spar of an emerald-green, purple, golden-yellow, bright pink or other colour are at first sight very different in appearance, and yet the difference is due solely to the presence of traces of colouring matters so small in amount that their exact nature is difficult or impossible to determine. The value of diamond, corundum and other gemstones depends largely on these accidental differences in colour. Such substances, which are essentially colourless and owe their colour to the presence of colouring matter as an impurity, are said to be “allochromatic”: any colour they may possess is nonessential. In some other substances, known as “idiochromatic,” the colour is a definite and essential character; for example, the yellow colour of gold, the red of cinnabar, &c.; but even here, owing to differences in the state of aggregation and the presence of various impurities, they may be wide variations in colour. Colour is thus a character of little determinative value, especially in minerals which are allochromatic; but it is sometimes a useful guide when taken in conjunction with other characters. An elaborate list of colour-names for descriptive use was drawn up by A. G. Werner in 1774.
An important character of transparent crystals is that of unequal absorption in different directions; so that light will, as a rule, be differently coloured according to the direction in which it has travelled through the crystal: this is known as dichroism or pleochroism (see Crystallography). Certain minerals (e.g. zircon, almandine and those containing cerium) when examined with a spectroscope by transmitted light exhibit characteristic absorption spectra.
The colours of minerals may also be due to the interference of rays of white light at the surfaces of thin crevices or minute inclusions, either tabular or fibrous in form, in the mineral; for example, the play of colours of opal; the change of colours of labradorite; the bands of rainbow colours (Newton’s rings) seen along cleavage cracks and irregular internal fractures (e.g. in quartz); the iridescent tarnish due to a superficial film of a, decomposition product (e.g. “peacock copper ore”); or the bluish opalescence of moon-stone and cat’s-eye.
The true colour of a mineral is best revealed by its “streak,” i.e. the colour of its powder. This is obtained by scratching the mineral, or by crushing a fragment of it on a sheet of white paper, or rubbing it upon unglazed porcelain. The streak of allochromatic minerals is white, while that of idiochromatic minerals is coloured and is often of determinative value. Ores of iron may, for example, generally be distinguished by their streaks: that of magnetite being black; haematite, blood-red; ​ limonite, yellow; and chalybite, white. The streak of a mineral may be either shining (e.g. argentite) or dull.
Another character depending on light is that of lustre, which is often very characteristic in certain minerals, though it may be considerably modified by the state of aggregation. For example, the usual adamantine lustre of diamond is not exhibited by the compact aggregate known as carbonado; while earthy masses of any mineral will be devoid of lustre. Descriptive terms applied to the kinds of lustre are: metallic (e.g. pyrites), adamantine (diamond), vitreous (quartz), resinous (pyromorphite), greasy (elaeolite), waxy (chalcedony), pearly (talc, heulandite and other minerals with a perfect cleavage), silky (satin-spar), &c. The degrees of intensity of lustre are described as splendent, shining, glistening, glimmering and dull, and depend usually on the smoothness of the crystal-faces.
The phenomena of phosphorescence (q.v.), fluorescence (q.v.) and radio-activity (q.v.) are strikingly exhibited by some minerals. (See Fluor-spar, Diamond, &c.)
b. Magnetic, Electrical and Thermal Characters.—These, as far as related to crystalline form, are discussed under crystallography (q.v.). Magnetite (“lode-stone”) is the only mineral which is strongly magnetic with polarity; a few others, such as pyrrhotite and native platinum, possess this character to a much less degree. Many minerals are, however, attracted by the pole of a strong electro-magnet, while a few (diamagnetic) are repelled. Most minerals with a metallic lustre are good conductors of heat and electricity; others are bad conductors. For example, graphite is a good conductor, while diamond is a bad conductor. Non-conductors of electricity become electrified by friction, some positively (e.g. quartz and topaz), others negatively (e.g. sulphur and amber). The length of time during which different gem-stones retain their charge of frictional electricity was made use of by R. J. Haüy as a determinative character. For the pyro-electrical and thermo-electrical characters of crystals see Crystallography. Some minerals—for example, salt, sylvite and blende—are highly diathermanous, i.e. transparent for heat-rays.
The specific heat and melting point of minerals are essential characters capable of exact measurement and numerical expression, but they are not often made use of. Different minerals differ widely in their “fusibility”: the following scale of fusibility was proposed by F. von Kobell:—
| 1. Stibnite | (525° C.) | 5. Orthoclase | (1175° C.) |
| 2. Natrolite | (965° C.) | 6. Bronzite | (1300° C.) |
| 3. Almandine | (1265° C.) | 7. Quartz | (1430° C.) |
| 4. Actinolite | (1296° C.) |
The melting points given above in parentheses were determined by J. Joly. Stibnite readily fuses to a globule in a candle-flame, while quartz is infusible even on the thinnest edges before the ordinary blowpipe.
c. Characters depending on Cohesion.—Some minerals (e.g. a sheet of mica) are highly elastic, springing back to their original shape after being bent. Others (e.g. talc) may be readily bent, but do not return to their original form when released; these are said to be pliable or flexible. Sectile minerals (e.g. chlorargyrite) may be cut with a knife without being fractured: related characters are malleability (e.g. argentite) and ductility (e.g. silver). The tenacity, or degree of frangibility of different minerals varies widely: they may be brittle, tough, soft or friable. The fractured surface produced when a mineral is broken is called the “fracture,” and the kind of fracture is often of determinative value; descriptive terms are: conchoidal (e.g. quartz, which may often be recognized by its glassy conchoidal fracture), sub-conchoidal, uneven, even, splintery (e.g. jade), hackly or with short sharp points (e.g. copper), &c.
In many cases when a crystallized mineral is broken it separates in certain definite directions along plane surfaces. This property of “cleavage” (see Crystallography) is an important essential character of minerals, and one which is often of considerable assistance in their recognition. For example, Calcite, with its three directions of perfect cleavage parallel to the faces of a rhombohedron, may always be readily distinguished from aragonite or quartz; or again, the perfect cubical cleavage of galena renders this mineral always easy of recognition.
“Hardness,” or the resistance which a substance offers to being scratched by a harder body, is an important character of minerals, and being a test readily applied it is frequently made use of. It must, however, be remembered that the hardness of an incoherent or earthy aggregate of small crystals will be very different from that of a single crystal. A comparative “scale of hardness” was devised by F. Mohs in 1820 for the purpose of giving a numerical statement of the hardness of minerals.
Mohs’s Scale of Hardness. :
| 1. Talc. | 6. Orthoclase. |
| 2. Gypsum. | 7. Quartz. |
| 3. Calcite. | 8. Topaz. |
| 4. Fluor-spar. | 9. Corundum. |
| 5. Apatite. | 10. Diamond. |
These minerals, arbitrarily selected for standards, are successively harder from talc the softest, to diamond the hardest of all minerals: a piece of talc is readily scratched by gypsum, and so on throughout the scale. A mineral which is capable of scratching calcite and itself be as easily scratched by fluor-spar is said to have a hardness of 31/2. Some care is required to avoid error in the determination of hardness: it is best to select a smooth crystal-face, cleavage-surface or fracture on which to rub a sharp corner of the scratching mineral; the powder should be wiped off and the surface examined with a lens to see if a scratch has really been produced or only powder rubbed off the corner of the mineral with which the scratching was attempted. With a little practice a fair idea of the hardness of a mineral may be obtained with the use of a knife or file, which will scratch all minerals with a hardness of 6 or less. Thus iron-pyrites (H. = 61/2) and copper-pyrites (H. = 31/2), apatite (H. = 5) and beryl (H. = 71/2), or gem-stones and their paste imitations may be readily distinguished by this test. Talc and gypsum can be readily scratched with the finger-nail.
Planes of parting, etching figures, pressure- and percussion-figures are sometimes characters of importance in describing and distinguishing minerals. (See Crystallography.)
d. Specific Gravity.—The density or specific gravity of minerals is an essential character of considerable determinative value. In minerals of constant composition it has a definite value, but in isomorphous groups it varies with the composition: it also, of course, varies with the purity of the material. It is a character which has the advantage of numerical expression: minerals range in specific gravity from 1·01 for copalite to 22·84 for iridium. The exact determination of the specific gravity of minerals is therefore a matter of some importance. Three methods are in common use, viz. hydrostatic weighing, the pycnometer, and the use of heavy liquids. The first two methods are only applicable when a weighable amount of pure material can be selected or picked out; this is, however, generally a laborious operation, since impurities are often present and usually several species of minerals are closely associated, and in selecting material it is often necessary to determine some other character to make certain that only one kind is being selected. For exact determinations the pycnometer method is usually to be recommended, using for material the pure fragments which have been selected for quantitative chemical analysis. With a single pure crystal or a faceted gem-stone the method of hydrostatic weighing is usually applicable, providing the stone is not too small. The most ready method, however, is that afforded by the use of a heavy liquid, and the most convenient liquid for this purpose is methylene iodide. This is a clear, mobile liquid with a specific gravity of 3·33, and by the addition of benzene, drop by drop, the specific gravity may be reduced to any desired amount. With such a liquid the specific gravity of the minutest fragment, the purity of which has previously been scrutinized under the microscope, may be rapidly determined. The liquid is diluted with benzene until the fragment just remains suspended, neither floating nor sinking; the specific gravity of the fragment will then be the same as that of the liquid, and the latter may be determined by hydrostatic weighing or, more conveniently, by ​means of indicators. Small recognizable crystals of the following minerals may be kept at hand as a set of indicators: gypsum (sp. gr. 2·32), colemanite (2·42), orthoclase (2·56), quartz (2·65), calcite (2·72), aragonite (2·93), rubellite (3·02), apatite (3·20), dioptase (3·32), &c. With a series of tubes containing mixtures of methylene iodide and benzene of different densities and suitable indicators, specific gravities may be rapidly and accurately determined. Values intermediate between those of the indicators may be estimated by a diffusion column of the liquid, or by noting the rate at which the benzene evaporates and the specific gravity of the liquid increases. For use with minerals of specific gravity greater than 3·33 various other heavy liquids have been suggested; the best being thallium silver nitrate (TlAg(NO$_3$)$_2$), which melts at 75° C. to a clear liquid with a density of 4·8, and is miscible with water.
e. Touch, Taste and Smell.—In their action on the senses of touch, taste and smell a few minerals possess distinctive characters. Talc is unctuous or soapy to the touch; tripolite and trachyte are respectively meagre and harsh. Some porous minerals (e.g. clays and hydrophane) adhere to the tongue. Gem-stones may often be distinguished from their glass imitation by the fact that they feel colder, since they are better conductors of heat. Bitumen and clays, when moistened, have a characteristic smell; pyrites and some other sulphides when rubbed emit a sulphurous odour. Minerals which are soluble in water have taste: e.g. saline (salt), alkaline (natron), bitter (epsomite), astringent (chalcanthite), &c.
3. Chemical Characters.
Chemical composition is the most important character of minerals, and on it all modern systems of classification are based. A mineral-species cannot, however, be defined by chemical composition alone, since many instances are known in which the same chemical element or compound is dimorphous or polymorphous (see Crystallography). Thus both the minerals diamond and graphite consist of the element carbon; both calcite and aragonite consist of calcium carbonate; and rutile, anatase and brookite consist of titanium dioxide. In such cases a knowledge of some other essential character, preferably the crystalline form, is necessary, before the mineral can be determined.,
All the known chemical elements have been found in minerals; and of many of them minerals are the only source. On the other hand, nitrogen, which is frequently present in organic substances, is rare in minerals; carbon has a wide distribution in mineral carbonates. It is estimated that the minerals of the earth's crust consist of about 47% by weight of oxygen, 27 of silicon and 8 of aluminium; silicates, and especially aluminosilicates, therefore predominate, these being the more important rock-forming minerals.
The chemical composition of minerals is determined by the ordinary methods of analytical chemistry. Since, however, minerals of different kinds usually occur intimately associated, it is often a matter of some difficulty to select a sufficiency of pure material for analysis. For this reason the exact composition and the empirical formulae of several minerals, particularly amongst the silicates, still remain doubtful. There are even cases on record in which the chemical composition and the crystalline form have been determined on different materials in the, belief that they were the same. Whenever possible, therefore, the chemical analysis should be made on small pure crystals which have been previously determined crystallographically. For the qualitative chemical examination of minerals, when only a small amount of material is available, the methods of blowpipe analysis and microchemical analysis are often convenient. (See G. J. Brush, Manual of Determinative Mineralogy, 16th ed., by S. L. Penfield, New York, 1903; H. Behrens, Manual of Microchemical Analysis, London, 1894.)
The principle of isomorphism (see Crystallography) is of the highest importance in mineralogy, and on it the classification of minerals largely depends. In some minerals (e.g. quartz) isomorphous or vicarious replacement is not known to occur; but in the majority of minerals one or other of the predominating elements (generally the base, rarely that of the acid radicle) may be isomorphously replaced by equivalent amounts of other chemically-related elements. In some isomorphous groups of minerals replacement takes place to only a limited extent, and the element which is partly replaced always predominates; while in other groups the replacement may be indefinite in extent, and between the ends of the series the different members may vary indefinitely in composition, with no sharp demarcation between species. Thus in the group of rhombohedral carbonates the different species are usually sharply defined. In well-formed crystals of calcite the calcium is replaced by only small amounts of magnesium, iron, lead, &c.; in chalybite, however, iron is often more largely replaced by calcium, magnesium, manganese, &c., and the “brown spars” are not always readily distinguishable. In the dimorphous group of orthorhombic carbonates isomorphous replacement is less frequent, and the different species (aragonite, cerussite, &c.) are quite sharply defined. In other groups of minerals, particularly amongst the silicates, isomorphous replacement of the basic elements is so general that the several members of the series vary almost indefinitely in chemical composition, and will scarcely be the same for any two specimens, though it may be reduced to the same type of formula. For example, the formula of all varieties of garnet may be expressed generally as R″ 3R‴$_2$(SiO$_4$)$_3$, where R″= Ca, Mg, Fe, Mn, and R‴= Al, Fe, Mn, Cr, Ti. Tourmaline affords another good example. In the plagioclase felspars (see Plagioclase) we have an example of the isomorphous mixing of two end-members, albite (NaAlSi$_3$O$_8$) and anorthite (CaAl$_2$(SiO$_4$)$_2$) in all proportions and with no sharp line between the several subspecies. In some other similar cases the end-members of the series are purely hypothetical: e.g. in the scapolite group (mixtures of Ca$_4$A1$_6$Si$_6$O$_{25}$ and Na$_4$Al$_3$Si$_9$O$_{24}$Cl) and in the micas and chlorites. In such instances, where the formulae of the two end-members differ in type, “mass effect” may have some influence on the isomorphism.
In addition to isomorphous series, there are amongst minerals several instances of double salts, which contain the same constituents as the members of isomorphous series: e.g. dolomite (q.v.) and barytocalcite (q.v.).
The manner in which water enters into the composition of minerals is often difficult to determine. In some cases, e.g. in the zeolites (q.v.), it is readily expelled at a low temperature, even at the ordinary temperature over sulphuric acid, and may be reabsorbed from a moist atmosphere or replaced by some other substances: it is then regarded as “water of crystallization.” In other cases, when expelled only at a higher temperature, it is to be regarded as “water of constitution,” forming either a basic salt (e.g. malachite, Cu(OH)$_2$CO$_3$) or an acid salt (e.g. dioptase, H$_2$CuSiO$_4$, and mica, q.v.). When present as hydroxyl it is often isomorphously replaced by fluorine (e.g. topaz, [Al(F,OH)]$_2$SiO$_4$). Sometimes the water is partly water of crystallization and partly water of constitution.
As to the actual chemical constitution of minerals the little that is at present known is mainly speculative. Dimorphous minerals, which have the same empirical formula may be expected to differ in constitution; and experiments have been made, for example on pyrites and marcasite, with the object of discovering a difference, but the conclusions of various investigators are not in agreement. More promising results have been obtained (by F. W. Clarke and others) by the action of various reagents on silicates, particularly on the more readily decomposed zeolites, and several substitution-derivatives have been prepared.
Synthesis of Minerals.—The production of minerals by artificial means is a branch of chemical mineralogy which has been pursued with considerable success, especially by French chemists. Most minerals have been obtained artificially in a crystallized condition, and many related compounds, not as yet found in nature, have also been prepared. Crystals of artificially prepared minerals, though usually quite small in size, possess all the essential characters of natural crystals, differing from these only in origin. The following are the principles of some of the ​ methods which have been used: simple sublimation (e.g. arsenolite); interaction of gases (e.g. haematite, from steam and ferric chloride; cassiterite, from steam and stannic chloride or fluoride); action of gases on liquids and solids; slow cooling of fused masses, either with or without the presence of agents rninéralisateurs (e.g. minerals in furnace slags); from aqueous solution sometimes at a high temperature and under pressure (e.g., quartz); electrolysis; or even by subjecting dry amorphous material to enormous pressure. The chemical reactions by which Various minerals have been obtained are often of considerable help in speculating as to their mode of origin in nature, though it must be born in mind that the same mineral may have been formed, both naturally and artificially, by more methods than one. In this direction important results have been obtained experimentally by J. H. van’t Hoff and his pupils on the formation of oceanic salt deposits, and by J. H. L. Vogt with slags. Many minerals used as gem-stones have been prepared artificially, e.g. diamond and ruby (see Gems: Artificial).
II.—Occurrence and Origin of Minerals.
While some minerals are of rare and sporadic occurrence in rock-cavities and mineral-veins, others are widely distributed as important constituents of rocks. The same mineral species may have several distinct modes of occurrence and origin, and be associated with different minerals in each case; facts which are well illustrated by quartz (q.v.).
Minerals of Igneous Rocks.—The rock-forming minerals of primary origin in igneous rocks have crystallized out from the magma, or fused silicate-mass, which on consolidation gave rise to the rock-mass. Magmas sometimes contain a considerable amount of water and are then in a state of aqueo-igneous fusion, rather than of dry fusion: in such cases very coarsely crystalline rocks (pegmatites) often result, and under these conditions minerals of many kinds are formed as well-developed crystals. Those minerals which are present in large amount in igneous rocks are distinguished as essential constituents, since it is on these that the classification of igneous rocks is largely based: the most important are quartz, felspars, pyroxenes, amphiboles, micas and olivines. Felspars of different composition are present in almost all kinds of igneous rocks, while quartz and olivine are characteristic of acid (e.g. granite, rhyolite) and basic (e.g. basalt, peridotite) rocks respectively. When the magma contains alkalies in relatively large amount the “felspathoid” minerals, nepheline and leucite, are formed (e.g. in nepheline-syenite, leucite-basalt, &c.). Other minerals occurring as primary constituents, but only in small amounts, are distinguished as accessory; thus small crystals of magnetite, apatite, zircon, &c., are of frequent occurrence disseminated in igneous rocks (see Petrology). Sometimes these accessory constituents are concentrated by magmatic differentiation, important ore-deposits sometimes resulting in this manner (e.g. of chromite, or nickel-bearing pyrrhotite). The alteration of igneous rocks by weathering and other processes results in the alteration of some or all of the primary minerals with the production of others, which are spoken of as secondary minerals: thus felspars are often partly or wholly altered to kaolin, olivine to serpentine, pyroxene and mica to epidote, chlorite, &c.
Minerals are also formed by the vapours given off by igneous magmas. The gases emitted by volcanoes and solfataras may deposit directly by sublimation, or by their chemical interaction, such minerals as sulphur, sal-ammoniac, haematite, which occur, for instance, as incrustations on Vesuvian lava: the boric acid of the Tuscan lagoons has also originated in this way. The effects produced by the exhalations of deep-seated magmas are more complex in character, since the vapours, being more confined, have more opportunity of acting chemically not only on the surrounding rocks but also on the igneous rock-mass itself before its final consolidation. A good example of the “pneumatolytic” action produced by the vapours from a mass of granitic magma is afforded by veins of tin-ore, in which the ore (cassiterite) is associated with minerals containing boron and fluorine, such as topaz, tourmaline. lepidolite, fluor-apatite and fluor-spar. The production of such minerals may be accounted for by assuming the presence of stannic fluoride in the vapours, which by reacting on water vapour would deposit cassiterite with the liberation of hydrofluoric acid, and this would again react on other minerals. The topaz and tourmaline crystals often found in the cavities of granites and pegmatites have doubtless been formed in this manner. In a similar way the exhalations of basic magmas have given rise to chlor-apatite with associated sphene and ilmenite, as, for example, in the extensive apatite veins in Connexion with gabbro in southern Norway.
Minerals of Metamorphic Rocks.—By the baking action of a deep-seated igneous mass on the surrounding rocks or on included rock-fragments, various new minerals are developed. By this process of thermal or contact-metamorphism well-crystallized examples of many minerals have often been formed; e.g. in calcareous rocks (limestones), especially those containing some magnesia and silica, vesuvianite, garnet, diopside, tremolite, wollastonite, &c., are developed; in argillaceous rocks (slates), chiastolite and staurolite are characteristic products; and in arenaceous rocks (sandstones), cordierite and sillimanite often result. The effects of pressure (dynamo-metamorphism) on rocks of various kinds, especially those of igneous origin, also result in the production of new minerals: e.g. pyroxene is transformed to amphibole, orthoclase to Muscovite, plagioclase to zoisite, olivine to tremolite, &c. In gneisses and crystalline schists, quartz, felspar, mica, talc, amphibole, &c. are important constituents.
Minerals of Sedimentary Rocks.—By the weathering and disintegration of igneous and metamorphic rocks the various minerals set free and the products of decomposition of others supply the material of sedimentary rocks; thus sandstones consist largely of quartz, shales of kaolin and other clay minerals. Those minerals (e.g. gem-stones and gold) which resist the action of weathering processes are found as water-worn pebbles and grains in detrital deposits. Other sedimentary rocks consist of minerals deposited from solution either by chemical or organic agencies, from sea-water, lakes or springs: e.g. the calcite of limestones, deposits of bog-iron-ore (limonite), gypsum, rocksalt, &c.
Minerals Segregated in Veins and Rock-cavities.—Water percolating through rock-masses takes up mineral matter in solution, and the solutions so formed may further react on the minerals composing the rocks. Such solutions will deposit some of their dissolved material in rock-cavities with the production of various minerals., For instance, the amygdaloidal cavities of basic volcanic rocks (e.g. basalt, melaphyre), especially when the rocks are somewhat weathered, are frequently partly or completely filled with agate or beautifully crystallized zeolites, calcite, &c. The crevices and joint-planes of limestone become in this way coated with crystals of calcite, and those of siliceous rocks with quartz, giving rise to the abundantly occurring quartz-veins. In sedimentary rocks, pyrites, flint and other minerals become segregated round a nucleus of organic matter. The beautiful crystal-lined crevices in the crystalline rocks of the Alps have much the same origin, and so have the various types of ore-deposits, including metalliferous veins or lodes. In the latter cases, however, the solutions are no doubt sometimes of deep-seated origin and often connected with igneous and metamorphic processes. Metalliferous veins are storehouses of crystallized minerals of almost every kind, some being the ores themselves and others, such as quartz, calcite, barytes, fluorspar, being gangue minerals. By the weathering of the metallic minerals of mineral-veins numerous other finely crystallized minerals result: for example, in the upper oxidized portion of Veins of lead-ore (galena), crystals of anglesite, cerussite and pyromorphite are often met with; in veins of copper-ore the alteration of chalcopyrite gives rise to malachite, chessylite and cuprite.
Alteration of Minerals: Pseudomorphs.—Crystals which have been formed under one. set of conditions of temperature and pressure and in the presence of certain solutions, will in many ​ cases be unstable under another set of conditions. The crystals may then be corroded or even completely redissolved, or the substance may undergo a chemical or physical change and give rise to the formation of other minerals which are stable under the new conditions. The results of such changes and alterations of minerals are very frequently to be observed in nature, and several instances have already been cited in the preceding section. A good example of the secondary products which may result by the decomposition of a mineral is afforded by pyrites (FeS$_2$), of which two types of alteration may be distinguished. By oxidation in the presence of pure water it gives rise to ferrous sulphate (melanterite), free sulphur and sulphuric acid; the melanterite by further alteration gives various basic ferric sulphates (copiapite, &c.); and the sulphuric acid by acting on surrounding rocks (limestone, clay, &c.) gives rise to the formation of gypsum, aluminite and other sulphates. By the action of water containing oxygen and calcium carbonate in solution, pyrites suffers another kind of alteration: the sulphur is carried away in solution as gypsum and the iron is left behind as a ferric hydroxide (limonite) which preserves the original form of the crystals. We have then a pseudomorph (from ψευδής, false and μορφή, form) of limonite after pyrites; i.e. limonite with the external form of a crystal of pyrites.
Pseudomorphs are frequently met with in nature, and they are of considerable importance in studying the changes which minerals undergo. Several kinds of pseudomorphs are to be distinguished. When the alteration has involved no change in chemical composition of the material, but only in the internal crystalline structure and physical properties, the altered crystal is called a “paramorph.” For example, crystals of aragonite are often altered to a confused granular aggregate of crystalline individuals of calcite, the change being accompanied by an increase in specific gravity but without change in external form: such a change may be effected artificially by simply heating a crystal of aragonite. Other examples of paramorphs are rutile with the form of anatase, and hornblende with the form of augite. An “epimorph” results from the encrustation of one mineral by another; the first may be afterwards partly or wholly dissolved out, leaving the second as a hollow shell (e.g. chalybite after fluor-spar). As instances of pseudomorphs in which there has been some chemical change the following may be cited: by the gain of chemical constituents, e.g. malachite after cuprite; by the loss of material, e.g. native copper after cuprite; or by an interchange of constituents, e.g. galena after pyromorphite and limonite after pyrites. In other cases there may be no evident chemical relationship between the two minerals, as, for example, in pseudomorphs of native copper after aragonite or quartz after calcite. Different minerals may also take the form of various organic remains.
III.—Nomenclature and Classification of Minerals.
A mineral species, or simple mineral, is completely defined by the statement of its chemical composition and crystalline form. When we are dealing with a definite chemical compound the limitation of species is easy enough; thus corundum, cassiterite, galena, blende, &c. are quite sharply defined mineral species. But with isomorphous mixtures the division into species, or into sub-species and varieties, must be to a certain extent arbitrary, there being no sharp lines of demarcation in many isomorphous groups of minerals. Thus in the mineral tourmaline the chemical composition varies indefinitely between wide limits, but no corresponding difference can be traced in the crystalline form or in the external characters save colour and specific gravity. Some authors have therefore questioned the advisability of separating minerals into species each with distinctive names, and they have attempted to devise chemical names for the different kinds of minerals. Owing, however, to the frequency of polymorphism and isomorphism amongst mineral substances such a system presents many practical difficulties. Thus the three modifications of titanium dioxide are more simply and conveniently referred to as rutile, anatase and brookite, while to give a purely chemical designation to such a mineral as tourmaline would be quite impracticable. Further, later investigations often show that such chemical names require revision, and hence confusion may arise.
The practice of giving distinct names to different kinds of minerals dates from very early times (e.g. diamond). The common termination ite (originally itis or ites) was adopted by the Greeks and Romans for the names of stones, the names themselves indicating some character, constituent, or use of the stone, or the locality at which it was found. For example, haematite, because of the blood-red colour; siderite, containing iron; alabaster (originally alabastritis), a stone from which a vessel called an alabastron was cut; magnetite, from the locality Magnesia. The custom of naming minerals after persons is of modern origin; e.g. prehnite, biotite, haüyne, zoisite. Unfortunately there is a lack in uniformity in the termination of mineral names, many long-established names being without the termination ite, e.g. beryl, blende, felspar, garnet, gypsum, quartz, zircon, &c. The termination ine is also often used, e.g. nepheline, olivine, serpentine, tourmaline, &c.; and many others were introduced by R. J. Haüy without much reason, e.g. anatase, dioptase, epidote, analcime, sphene, &c. (see A. H. Chester, A Dictionary of the Names of Minerals, New York, 1896).
The number of known mineral species differs, of course, according to different authors; roughly there may be said to be about a thousand. The total number of mineral names (apart from chemical names), many of them being applied to trivial varieties or given in error, amount to about 5000.
Minerals may be classified in different ways to suit different purposes; thus they may be classified according to their uses, modes of occurrence, system of crystallization, &c. The earlier systematic classifications, being based solely on the external characters of minerals, were on natural history principles and too artificial to be of any value. J. J. Berzelius, in 1815, was the first to propose a purely chemical system of classification: his primary divisions depended on the basic (electro-positive) element and the sub-divisions on the acid (electro-negative) element. Such a method of classification, though still in use for metallic ores, must be quite arbitrary or give rise to much duplication; since, apart from isomorphous replacement, many minerals contain more than one metal. The systematic classifications in use at the present day are modifications in detail of the crystallo-chemical system published by G. Rose in 1852. Here there are four main divisions, viz. elements; sulphides, arsenides, &c.; halogen compounds; and oxygen compounds: the last, and largest, division is subdivided into oxides and according to the acid (carbonates, silicates, sulphates and chromates, phosphates and arsenates, &c.); in each section isomorphous minerals are grouped together. The classifications adopted by different authors differ much in detail, especially in the large section of the silicates, which presents many difficulties and for which no satisfactory classification has yet been devised.
As an example of a systematic classification of minerals the following may be given. Except in a few details it is the classification of Dana’s System of Mineralogy (6th ed., 1892). Only those minerals which are described under their respective headings in these volumes are included: the list therefore serves, at the same time, as an enumeration of the more common and important species and varieties of minerals, and as a system of classification it is necessarily incomplete. Species belonging to the same isomorphous group are bracketed together: varieties are given in parentheses after the species to which they belong. The chemical composition of each species is given by the formula; and the crystal-system by the initial letters C (cubic), T (tetragonal), O (orthorhombic), M (monoclinic), A (anorthic), H (hexagonal) and R (rhombohedral): when the crystal class is definitely known to be some other than the holosymmetric this is indicated by a number corresponding to those used in the article Crystallography, e.g. C$_2$ for the tetrahedral class of the cubic system.
I.—NATIVE ELEMENTS. :
| 1. Non-Metals. ||
| | Diamond | C | C2 |
| | (Bort, Carbonado) |
| | Graphite | C | R |
| | Sulphur | S | O |
| 2. Semi-Metals. ||
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Arsenic | As | R |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Antimony | Sb | R |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Bismuth | Bi | R |
| 3. Metals. ||
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | Gold | Au | C |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | Silver | Ag | C |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | Copper | Cu | C |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$ | Platinum | Pt | C |
| II.—SULPHIDES, ARSENIDES, TELLURIDES, ETC. ||||
| 1. Of the Semi-Metals. ||
| | Realgar | AsS | M |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | Stibnite | Sb$_2$S$_3$ | O |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | Bismuthite | Bi$_2$S$_3$ | O |
| | Tetradymite | Bi$_2$Te$_2$S | R |
| | Molybdenite | MoS$_2$ | R |
| 2. Of the Metals. ||
| A. Monosulphides, &c. ||
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | Argentite | Ag$_2$S | C |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | Galena | PbS | C |
| | Copper-glance | Cu$_2$S | O |
| | Blende | ZnS | C2 |
| | Cinnabar | HgS | R3 |
| | Covellite | CuS | H |
| | Greenockite CdS | R2 |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Millerite | R |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Niccolite NiAs | R |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Pyrrhotite | Fe$_{11}$S$_{12}$ | R |
| B. Intermediate Division. ||
| | Erubescite | Cu$_5$FeS$_4$ | C |
| | Chalcopyrite | CuFeS$_2$ | T2 |
| C. Disulphides, &c. ||
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Pyrites | FeS$_2$ | C3 |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Smaltite | CoAs$_2$ | C3 |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$ | Cobaltite | CoAsS | C3 |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | Marcasite | FeS$_2$ | O |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | FeAsS | O |
| | Sylvanite | AuAgTe$_4$ | M |
| III.—SULPHO SALTS. ||||
| | Freieslebenite | (Pb,Ag$_2$)Sb$_4$S$_{11}$ |
| | Bournonite | PbCuSbS$_3$ | O |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | Pyrargyrite | Ag$_3$SbS$_3$ | R2 |
| $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ | Prousite | Ag$_3$AsS$_3$ | R2 |
| | Tetrahedrite | Cu$_3$SbS$_3$ | C2 |
| | Stephanite | Ag$_5$SbS$_4$ | O2 |
| | Cu$_2$FeSnS$_4$ | T2 |
| | Argyrodite | Ag$_8$GeS$_6$ | C |
| IV.—HALOIDS. ||||
| 1. Anhydrous ||
| | Salt | NaCl | C |
| | Sylvite | KCl | C4 |
| V.—OXIDES. ||||
. . . . . . Ilmenite FeTiO$_3$ R4 c. Intermediate Oxides. Spinel MgAl$_2$O$_4$ C Magnetite FeFe2O4 .... C Franklinite (Fe, Zn, Mn)(Fe, Mn)gO4 C Chromite (Fe, Mg)(Cr, Fe)2O4 C Chrysoberyl BeAl2O4 .... O (Alexandrite, Cymophane) d. Dioxides Cassiterite S11O2 T Rutile TiO2 T Anatase TiO2 T Brookite TiO2 O Pyrolusite MnO2 P Pitchblende (U, Th)O$_2$ C B. Hydrous Oxides. Diaspore AlO(OH) O Goethite FeO(OH) O Manganite MnO(OH) .. O Limonite Fe2O3.3H2O Amorphous Bauxite . Al$_2$O$_3$.2H$_2$O? Brucite Mg(OH)2 . R Psilomelane xMnO2+yBaO-I-HQO Amorphous (Wad) VI.—OXYGEN SALTS. I. Carbonates. A. Anhydrous. Calcite ... CaCO3 R (Satin-spar) Dolomite CaMg(CO3)2 R4 Ankerite Ca(Mg, Fe)(CO3)2 R Magnesite MgCO3 R Chalybite FeCO3 R Rhodochrosite. MnCO3 R Calamine . ZnCO3 R Aragonite CaCO3 O Alstonite (Ca, Ba)CO3 O Witherite BaCO3 O Strontianite SrCO3 O Cerussite PbCO3 .. O Barytocalcite CaBa(CO3)2 M Parisite (CcF)2Ca(CO3)3 H Phosgenite (PbCl)2CO3 T B. Basic Carbonates. Malachite Cu2(gH)2CO3 M Azurite Cu3 H 2 CO3 2 M 2. Silicates. A. Anhydrous Silicates. a. Disilicates, R″Si1O5; Pol;/silicates, R"Si3Og Petalite LiAl (Si2O5)z M Orthoclase KAlSi3Og M (Moon-stone) Microcline KAlS13O8 A (Amazon-stone) Albite NaAlS1;, Og A Oligoclase Ab6An1 to Ab3An1 A (Sun-stone) Andesine Ab3An1 to Ab1An1 A Labradorite Ab1An1 to Ab1An3 A BytoWnite Ab1An3 to Ab1An6 A Anorthite CaAl$_2$Si$_2$O$_8$ b Metasilicates, R″ SiO$_3$. Leucite KAl(SiO$_3$$_2$ Pseudo-C Pollux H$_2$Cs$_4$Al$_4$(SiO$_3$)$_9$ C Enstatite MgSiO$_3$ . O Bronzite (Mg, Fe)SiO3 O Hypersthene (Fe, Mg)S1O3 O Diopside CaMg(SiO3)2 .... M Augite . 3 Ca(Mg, Fe) (SiO3)2 M  (Diallage) § 1tPh(M§ éF5)§ Al, Fe)2SiO¢ M Acmite a e”' i 32 Spodumene . LiAl(SiO3)2 . M  (Hiddenite, Kunzite) Jadeite NaAl(SiO3)2 M Wollastonite CaSiO3 M Rhoddnite MnSiO3 A Tremolite .... CaMg3(SiO3)4 M [Actmolite] . Ca(Mg, Fe)3(S1O3)4 M (Asbestos, Nephrite) Ca(Mg, Fe)$_3$(SiO$_3$)$_4$ Hornblende with NaAl(S1O3)¢ M and (Mg Fe) (Al, Fe)4(SiO5)2 Crocidolite gage FeSiO3 % Beryl Be$_3$Al$_2$(SiO$_3$)$_6$ (Aquamarine, Emerald) c. Intermediate. Iolite .... H$_2$(Mg, Fe)$_4$Al$_8$Si$_{10}$O$_{37}$
d. Orthosilicates, R″2SiO$_4$.
Nepheline .... K$_2$Na$_6$Al$_8$Si$_9$O$_{34}$ .... H5 Sodalite .... Na4(AlCl)A1 < »o.> C Lazurite] .... Na4(Na5a.Al)Ala(S10a)s C (Lapis-lazuli) Grossularite] Ca3Al2(SiO4)3 .... C (Cinnamon-stone)-Pyrope Mg3Al2(SiO4)3 C Almandine Fe3Al2(SiO4)a . C Andradite] Ca3Fe2(SiO4)s C (Demantoid) Olivine .... (Mg, Fe)2SiO4 O (Chrysolite, Peridot) Phenacite .... Be2SiO4 R4 Willemite .... Zn2SiO4 .... R4 Dioptase R4 - M H4 6 ls 25 Scapolite - - - 'inNa A1 si 0 c11r ° ' T3 Vesuvianite H2Ca5(Al, Fe)3Si5O1g T Zircon .. ZrSiO4 . .. T (Hyacinth, jacinth, jargoon) Thorite .... ThSiO4 T Danburite . .. CaB2(SiO4)2 O Topaz [Al(F, OH)]2SiO4 O Andalusite. Al2SiO5 O Sillimanite. .Al2SiO5 O Cyanite Al2SiO5 A Datolite HCaBSiO5 M Euclase HBeAlSiO5 .. . M Zoisite Ca2(AlOH)Al2(SiO4)3 O Epidote Ca2(AlOH) (Al, Fe)2(SiO4)3 M Axinite HCa3BAl2(SiOi)4 A Prehnite HzCa2Al2(SlO4)3 O2 e. Subsilicates. Humite ... Mg5[Mg(F, OH)]2(SiO4);¢ O Hemimorphite H2Zn2SiO5 .... O2 Tourmaline (H2, Na2, Mg)3(Al, Fe)6(BOH)4 (Rubellite) Si O38 . ... R2 Staurolite . HFeAl5Si2O|3 . O B. Hydrous Silicates Apophyllite H1KCa4(SiO3)@+4%H2O. T Heulandite H4CaAl2(SiO3). +3H2O M Phillipsite (K2, Ca)Al2(SiO3)4+4H2O M Harmotome H2(Kz|Ba)Al2(SiO3)5-|-5H2O M Stilbite § CaAl2(SiOa)c+6H2O M Chabazite Ca, Na2)Al2(SiO4)2-I-4H2O, &c R Analcite NaAl(SiO3)2-l-H20 C Natrolite Na2Al2Si3Oio'|'2H2O O Scolecite CaAl2Sl3O10+3H2O ri Muscovite H2KAl3(SiO.i)3 M Lepidolite KLi[Al(OH, F)2]Al(SiOs)a M Biotite (H, K)2(Mg, Fe)2Al2(SiO4)3, &c.M Phlogopite [H, K, (MgF)]:ilVlgaAl(SiO4)3 M Clintonite H2(Fe, Mg)Al2SiO7, &c. M Chlorite H (Mg, Fe)5Al2Si3O1a &c. M Serpentine HiMg3Si2O9 .. M Talc H2Mg3(SiOa)4 M Meerschaum H4Mg2S1301D Amorphous Kaolin . H4Al2Si2O9 M (Bole, Clay) Pyrophyllite HAl(SiO3)2 M? Allophane Al2SiO5+5H2O Amorphous Chrysocolla CuSiO3+2H2O, , C. Titano-silicates, Titanates Sphene . CaTiSiO5 M Perofskite CaTiO3 Pseudo-C 3. Niobates, TANTALATES. Columbite (Fe, Mn)(Nb, Ta)¢O5 O 4. PHOSPHATES, ARSENATES, &c A. Anhydrous Phosphates, &'c. Monazite . (Ce, La, Di)PO4 M Beryllonite NaBePO4. O Apatite [Ca(F, Cl)]Cai(PO4)3 H2 (Phosphorite) Pyromorphite (PbCi)Pb4(PO4)3 H2 = Minietite (PbCl)Pb4(AsO4)a H2 Vanadinite (PbCl)Pb4(VO4)a H2 Amblygonite Li(AlF)PO4 A B. Basic Phosphates, &c. Olivenite Descloizite Clinoclasite C. Hydrous Phosphates, &c. Vivianite . . Erythrite Annabergite Wavellite . . Cu2(OH)AsO4 O (Pb, Zn)2(OH)VO4 O CU3(OH)3ASO4 M Fe3(PO4)2'l'8H2O M CO3(ASO4)2+8H2O M Ni3(AsO4)2+8H2O M Al3(OH)s(PO4)2“l'4iH2O O Turquoise. [Al(OH)2, Cu(OH), H]3PO4Amorph. Pharmacosiderite Fe3(OH)3A5O¢ C2 Childrenite (Fe, lVln)Al(OH)2PO4-{-H20 O Liroconite ... CU3Al4<OH)15(ASO4)5+2OH2O M Torbernite Cu(UO2)2(PO4)2+ I2H2O T Autunite Ca(UO2)2(PO4)2+I2H2O O
5. BORATES. Boracite Mg7Cl2B15O30 Pseudo-C2 Colemanite Ca2B5O1, -|-5HzO .. Borax
6.Nitrates
7. Sulphates and Chromates
8. Tungstates, Molybdates Wolframite (Fe,Mn)WO4 Scheelite CaWO4 Wulfenite PbMoO4
VII.—HYDROCARBON COMPOUNDS.
1. Simple Hydrocarbons. Hatchettine, Ozocerite..
2. Oxygenated Hydrocarbons. Amber, Retinite, Copaline, Bathvillite, Dopplerite.
3. Appendix to Hydrocarbons. Petroleum, Asphaltum, Bitumen, Elaterite, Albertite, Coal, Anthracite, Jet, Lignite
References.—Elementary introductions to the study of minerals are: E. S. Dana, Minerals and how to study them (New York, 1895); A. J. Moses and C. L Parsons, Elements of Mineralogy, Crystallography and Blowpipe Analysis from a Practical Standpoint (4th ed., New York, 1909); L. Fletcher, An Introduction to the Study of Minerals (British Museum Guide-book). A larger work on popular lines is: R. Brauns, The Mineral Kingdom, Eng. trans. by L. J. Spencer (Stuttgart, 1908, &c). Textbooks for students are: H. A. Miers, Mineralogy, an Introduction to the Scientific Study of Minerals (London, 1902); E. S. Dana, Textbook of Mineralogy 3rd ed., New York, 1898); and in German: C. F. Naumann, Elemente der Mineralogie (15th ed., by F. Zirkel, Leipzig, 1907); G. Tschermak, Lehrbuch der Mineralogie (6th ed., Vienna, 1905). The standard works of reference for descriptive mineralogy are: J. D. Dana, System of Mineralogy (6th ed., by E. S. Dana, New York, 1892); C. Hintze, Handbuch der Mineralogie (Leipzig, 1898, &c.), the latter gives full details respecting the localities of minerals; P. Groth, Chemische Krystallographie (Leipzig, 1906, &c).
For special branches of mineralogy reference may be made to the following works: R. Brauns, Chemische Mineralogie (Leipzig, 1896); H. Roseubusch, Mikroskopische Physiographie der Mineralien und Gesteine, Band I, Die petrographisch-wichtigen Mineralien, 4th ed., by H. Rosenbusch and E. A. Wülfing (Stuttgart, 1904-1905); J. P. Iddings, Rock Minerals (New York, 1906); P. Groth, Tabellarische Ubersicht der Mineralien (4th ed., Braunschweig, 1898); G. P. Merrill, The Non-metallic Minerals, their Occurrence and Uses (New York, 1904); G. J. Brush, Manual of Determinative Mineralogy (16th ed., by S. Pentield, New York, 1903); M. Bauer, Edelsteinkunde (2nd ed., Leipzig, 1909), and Eng. trans. Precious Stones, by L. J. Spencer (London, 1904).
The more important topographical works are: R. P. Greg and N. G. Lettsom, Manual of the Mineralogy of Great Britain and Ireland (London, 1858); J. H. Collins, Handbook to the Mineralogy of Cornwall and Devon (Truro, 1871); M. F. Heddle, Mineralogy of Scotland (2 vols., Edinburgh, 1901); A. Lacroix, Minéralogie de la France et de ses colonies (3 vols., Paris, 1893, &c.); O. Luedecke, Die Minerale des Harzes (Berlin, 1896); A. Frenzel, Mineralogisches Lexicon für das Königreich Sachsen (Leipzig, 1874); A. Kenngott, Die Minerale der Schweiz (Leipzig, 1866); V. von Zepharovich, Mineralogisches Lexicon für das Kaiserthum Österreich (3 vols., Vienna, 1859-1893); N. von Koksharov, Materalien zur Mineralogie Russlands (11 vols., St Petersburg, 1853-1882); T. Wada, Minerals of Japan (Tokyo, 1904); A. Liversidge, The Minerals of New South Wales, &c. (London, 1888); O. B. Böggild, Mineralogia Groenlandica (Copenhagen, 1905); A Catalogue of American [U.S.A. and Canada] Localities of Minerals is given in Dana's System of Mineralogy.
The following scientific journals are devoted to mineralogy: Neues Jahrbuch für Mineralogie, &c. (Stuttgart, since 1807); Tschermaks Mineralogische und petrographische Mitteilungen (Vienna, since 1872); The Mineralogical Magazine and Journal of the Mineralogical Society (London, since 1876); Zeitschrift für ​Krystallographie und Mineralogie, ed. by P. Groth (Leipzig, since 1877); Bulletin de la société française de minéralogie (Paris, since 1878); Rivista di mineralogia e cristallografia (Padova, since 1887). (L. J. S.)
* ↑ This is from a German word, druse, originally meaning “brush,” and applied by miners to hollow stones, lined with minute projecting crystals.
* ↑ Often classed with the titanates.
* ↑ Often classed as aluminates
* ↑ Usually classed as a uranate