Mineralogy, the science which treats of the composition, structure, formation, and classification of minerals. The term therefore covers both descriptive mineralogy and mineral-ology, which is the study of the laws in accordance with which minerals are formed. All objects in nature consist of certain substances recognized as elementary bodies, which exist either as individual wholes, when they are called native elements, or combined with one another. All the native elements belong to the mineral kingdom, and also all combinations of elements which do not pass through the cycle of change called growth. The combinations of the elements which man produces all belong to the mineral kingdom, since he is not able to impart the principle of growth. When his products are homogeneous in composition and structure, they are, strictly speaking, artificial minerals; and chemists are able to reproduce a great number of the combinations found in nature. The study of minerals presents three general classes of characteristics: chemical composition, crystalline form, and physical properties. I. Chemistry of Minerals. In combining, the elements exhibit a strict subjection to certain fixed modes of union, and these modes are the laws of chemical combination, which are still very imperfectly understood.

Chemists recognize two kinds of units. The smallest possible particle of an elementary substance is called an atom. These atoms seem to exist in a state of polarity, and to possess electrical attraction and repulsion, by means of which they effect union with each other and with the atoms of other elements. They are not always able to exist by themselves, but the atoms of some elements act in pairs or triplets, or in some other degree of union. This combination of atoms, whether composed of the atoms of more than one element, or of one only, is called a molecule. Molecules have the power of cohesion, and by their aggregation masses of matter are formed. Both of these units are used in mineralogy. Every true mineral is formed of innumerable molecules cohering together, and each of these molecules is composed of one or more atoms of each element contained in the mineral, according to the proportion in which it is present. While there is unending diversity in the composition of minerals, it is found that the elements always unite in some simple proportion or ratio. Three kinds of ratios are used in mineralogy. The percentage ratio is the one in which analyses are always published.

It assumes the weight of each molecule to be 100, and expresses the proportionate quantity of each element in the molecule in parts of 100. Lime, for instance, contains 71'43 per cent, of calcium and 28.57 per cent, of oxygen. The atomic ratio is the ratio between the number of atoms of each element in the molecule, and is obtained by simply dividing the percentage ratio of each element by its atomic weight. When the symbol of a mineral is given, the atomic ratio may be ascertained by simple inspection of the symbol. In lime, the symbol of which is CaO, the molecule is composed of 1 calcium and 1 oxygen, and the atomic ratio is therefore 1:1. In andalusite, which is composed of Al2O5Si, the atomic ratio of the aluminum, oxygen, and silicon is 2: 5: 1; while if the oxygen is divided between the aluminum and silicon, the compound will be considered as formed of two radicals, alumina and silica, and the atomic ratio of these will be 1: 1, there being one of each. The third method of comparison is the oxygen ratio; it consists in a comparison of the number of oxygen atoms contained in the different oxygen compounds present. In andalusite, for instance, the alumina has three oxygen atoms and the silica two.

The O ratio is therefore 3: 2. The explanations so far given relate to the old method of writing chemical symbols. The new chemistry reaches the same results by a different mode of reasoning. Every binary compound consists of one positive and one negative element. Every ternary compound consists of one positive element, a second which is negative to the first but positive to the third, and finally a third which is negative to both the others. The number of negative atoms in a binary compound is found to vary with the different elements, each element having the power to fix a certain number of atoms of a more negative element; this power is called its atomicity or quantivalence. All of the stable binary compounds of hydrogen are found to contain one atom of hydrogen and one of the other element, whatever it is; and hydrogen is therefore taken as the standard. By comparing the other elements with it, it is found that 23 of them have a combining power equal either to 1, 3, or 5 hydrogen atoms; and these are therefore called univalent, triva-lent, or quinquivalent. These never form stable saturated compounds with any even number of negative univalent atoms, and they are therefore called perissads, from the Greek word for odd numbers.

The remaining 40 elements have a combining power which is 2, 4, or 6 times that of hydrogen, and they are therefore bivalent, quadrivalent, and sextiva-lent. These form the general class of artiads, and are never saturated when combined with an odd number of negative univalent atoms. The highest possible combining power of an element is called its atomicity, but this is not always the most common form of its occurrence, which is often one of the lower degrees; this prevalent form is its quantivalence. The oxygen ratio, although it was used with the best results in mineralogy long before the new chemical theories were established, is nothing more than the expression of the relative quantivalences of the different elements contained in a mineral. Oxygen is in all cases a negative element, and the number of its atoms which are combined with one atom of any other element, taken in connection with the doubled atomic weights of the new chem-istrv, indicates the relative quantivalences of thecombined elements. The change of ideas in regard to the modes of combination has necessarily produced a new mode of writing the symbols of minerals.

Under the dualistic theory, when every ternary oxygen compound was supposed to consist of one oxide acting the part of a base and another oxide acting the part of an acid, the formula was constructed by writing the two compounds one after the other, as RO,Si02, or R,O3,3SiO2, in which R stands for any basic element. The new system endeavors to make its formulas rational, that is, to construct them in such a way as to embody the present views in regard to chemical combination. The elements are divided into three classes: 1 the basic, which are positive to those following; 2, the acidic, which are negative to the foregoing, but positive to the third class; 3, the aeidific, which are negative to both the first and second. In a ternary compound which consists of one element from each of these classes, the aeidific element is supposed to act as a bond between the other two, and for that reason it is placed in the middle, the basic being written first, the acid-ilic next, and the acidic last; as Mg2 || O4 || Si. It has been explained that one atom of each element has the power of uniting to itself a certain number of atoms (from one to six) of hydrogen or other univalent element; and just as the ancients provided the elements with hooks by which they caught hold of each other, so modern chemists express the quanti-valence of an element by saying that it has a certain number of bonds of attraction.

Magnesium has a quantivalence of 2, and as there are two molecules of it in the above symbol, the total number of its bonds in the formula just given is four. Silicon has a quantivalence of 4. so that the oxygen has four bonds to satisfy on each side, or eight in all. As its quantivalence is 2, the four molecules present in the compound have a total uniting power of eight. Hut the whole of the oxygen does not always play the part of a uniting element only. The number of molecules of uniting oxygen (or other aeidific element) is equal to the number of bonds of attraction in the basic or acidic element, according as the former or the latter has the smaller number. In the symbol given above, the number of oxygen bonds is just sufficient to satisfy those of the other alements, but in the symbol Mg03Si there are two bonds on one side of the oxygen and four on the other. In this case part of the tygen is considered to be combined with that element which has the greater number of bonds to be satisfied. When this is the acidic element, as m the present case, the symbol is written with the acidic element at the left side: as Si() || O9 || Mg. If the basic element had possessed the greater quantivalence, that element would have been written at the left; as in the symbol for chondrodite, Mg8O2|| (0,F)12 || Si3. Thus the symbols are made to express the mineralogist's views of the constitution of minerals. - Replacement. Minerals in their chemical composition are elementary, binary, ternary, quaternary, etc, according as the number of molecules of which they are composed is one, two, three, or four, etc.

This, however, does not indicate the possible number of elements present, since each molecule may contain several elements. Enstatite, which is composed of magnesium, oxygen, and silicon, is a ternary; and diaclasite, which has magnesium, iron, calcium, oxgygen, and silicon in its composition, is also only a ternary, since the first three elements form only one basic molecule. In this case each element in the basic molecule is a dyad (that is, it has a quantivalence of 2), and it may not seem strange that, with equal powers of combination, they should be able to replace each other. But other minerals are found which contain elements of the most diverse degrees of quantivalence, and therefore in the most diverse states of combination. Zircon sometimes contains a protoxide, a sesquioxide, and a deutoxide. The law under which these diverse combinations are brought harmoniously together is that " the replacing power of the elements is in proportion to their combining power." Thus one molecule of an element which has four bonds of attraction, like tin, is able to replace two molecules of an element which has only two bonds of attraction, like calcium.

In stannite, which is a sulphide of copper, tin, and iron, the proportions of these elements are 2:1:1. Copper, which is bivalent, requires two atoms to occupy toward sulphur the same relation which one atom of tin and iron has. The proportion in which any element in any state of combination must replace other elements in a different state may be ascertained from the following table, in which the line A contains the several oxides that are known, the line B contains the same oxides reduced to a common oxygen standard (0=1), and the line 0 represents the proportions in which the bases are interchangeable. The different states are represented by Greek letters in order to avoid confusing fractions. Thus the beta state is sesquioxide and the gamma state is the deutoxide. R is used to represent any basic element, and it is to be remembered that, though only oxides are represented here, the rule holds good for all negative elements.

A. RO, R203, RO2, R205, R0S, R207, RO4.

B. R2/3O, R2/3O, R1/2O, R2/5O, R1/30, R2/7O, R2/7O.

C. αR, βR, γR, δB, εR, ζR, ηR.

Any element in the tritoxide state (εR) therefore requires but one basic atom to replace three basic atoms of an element in the protoxide or alpha state. The method of writing the symbol of a mineral which has suffered such substitution may be seen from the symbols of magnetite and franklinite. The former contains iron in the alpha and in the beta stato of combination with oxygen. Its symbol is (1/2αFe + 3/4βFe)404, and it is therefore a binary compound. In franklinite the αFe is partially replaced by zinc and manganese in the alpha state, and the βFe is partially replaced by manganese in the beta state. The symbol then becomes [i(Zn,Fe,Mn) + 3/4βFe,βMn)]404. The a is not written, the protoxide state being understood when no other is mentioned. The effect of the law of replacement is, that whatever kinds of binaries may be united in the mineral, the oxygen ratio is unchanged, and the use of this ratio is therefore continued in mineralogies, though the oxygen is no longer considered to be divided between the basic and acidic elements. It expresses the quantivalence of these elements, and this is held to be one of the most essential characteristics of a mineral species.

While the power of replacement has greatly increased the number of mineral species by presenting us with compounds which vary too much to be described under one name, it has lessened the number of groups in an equally marked degree, since the substitution often takes place without materially altering the other characters. Thus tourmaline, which is a ternary, sometimes contains 12 elements, and the basic molecule always contains elements in the alpha, beta, and gamma states. Their proportions vary so much that five classes have been made in which the O ratio of these three kinds of bases varies between 4: 12: 4 and 4: 56: 12; and yet tourmaline is usually very plainly recognizable and possesses very persistent crystallographic habits. - Chmifica-tion of the Elements. With the foregoing explanations the following table in which the elements are classified will be understood:

Classification Of The Elements

Series I.

Series II.

Series III.

A. Perissads.

A. Perissads.

A. Perissads.

Potassium, sodium, caesium, rubidium, lithium, thallium, hydrogen, silver, gold.

Nitrogen, phosphorus, arsenic, antimony, bismuth, columbium, tantalum in the δR state, boron (?).

Chlorine. Bromine. Iodine.

B. Artiads.

B. Artiads.

B. Perissad (or Artiad).

1. Iron-aluminum group.

1. Sulphur group.

a. Iron sub-group: platinum, palladium, iridium, rhodium, osmium, ruthenium, copper, lead, mercury, iron, zinc, indium, cadmium, cobalt, nickel, manganese, chromium, uranium, tungsten, cerium, erbium, yttrium, glucinum, lanthanum, didymium, magnesium, calcium, strontium, barium ; also H2, K2, Na,, etc.

Sulphur, selenium, tellurium, molybdenum ; also εFe, εCr, εMn, εV, εW.

Fluorine.

C. Artiad.

6. Aluminum sub-group: aluminum (βA1); also βFe, βMn, βCr, βB, etc.

Oxygen.

2. Tin group.

2. Carbon-silicon group.

Tin, titanium, zirconium, thorium; also γH2, γFe, γMn, γCo, γPb, γCu, &c

Carbon, silicon; also γS, γSe, γTe. etc.

The three kinds, basic, acidic, and acidific, are arranged in three series. Each series begins with a section of perissads, or elements with a quantivalence which is 1, 3, or 5, and ends with a section of artiads, or elements which have a quantivalence of 2, 4, or 0, thus bringing together allied elements. The basic artiads comprise two groups, one of protoxides and sesquioxides, and the other of deutoxides. The acidic artiads form a tritoxide and a deutoxide group. It is therefore plain that each group is made up of elements which occur in the same state of combination, or have the same quantivalence, and the groups might with perfect propriety be called the alpha, beta, etc, groups. Each group therefore includes not only its own leading elements, but also the α, β, or γ, etc, states of other elements; and therefore each group comprises a series of homceo-morphous (or mutually replaceable) elements.

II. Crystalline Form

Atoms are supposed to have definite shapes, for the greater number of the mineral species have exact geometrical forms which have been classified in six systems. (See Crystallography.) The atomic form seems to be different for the different elements; and since the same element is sometimes found crystallized in more than one system, it is supposed that the number of atoms in the molecule influences its shape. Thus the mineral species palladium is the native element of the same name, and crystallizes in the isometric system; while allopalladium, which is also the native element in a pure state, is hexagonal. The theory is that, while the molecule of palladium contains one atom, the molecule of allopalladium contains three atoms of the same substance. The diamond (isometric) and graphite (hexagonal) are both carbon, and form another example of this phenomenon, which is called isomerism. A great many of the compounds are identical in composition, but differ in form. Andalusite, fibrolite, and cyanite have the same composition, but crystallize in different systems, and have a different hardness and specific gravity; and these differences are ascribed to a more or less condensed molecule, but what the numerical relation of the atoms in these molecules is, has not been established.

It has, however, been suggested that the forms assumed may be due to the number of negative atoms in the molecule. Thus protoxides may assume isometric forms, deutoxides may be tetragonal, and tritoxides hexagonal. While this theory is not entirely borne out by the facts, it would probably be more eminently plausible if other portions of our system were more perfect. Thus, though protoxide, like water and zincic oxide, take the hexagonal instead of the isometric form, this fact leads mineralogists to look upon these minerals as being composed of condensed molecules containing three atoms of each element, and to write their symbols, H603 and Zn3Os, rather than reject the theory. This theory-does not account for all the examples of polymorphism, nor can they be accounted for without greater knowledge of the crystalline systems. Certain forms in some of the systems, when placed in a particular position, are identical both in position and angle of the faces, with others in entirely different systems. Nevertheless, none of the efforts to reduce the crystallographic systems below six have been successful. It is, however, established that minerals may be isomorphous with others crystallizing in a different system, when their angles are nearly similar.

The variations in the six systems depend upon the relative length of their axes; and when the axial dimensions of two minerals in different systems are nearly the same, they may enter into chemical or physical combination without violence to their individual laws of formation. The likelihood of such replacement is increased by the fact that the crystallographic forms of minerals, though precise in general, are not perfectly uniform in angle. Even the most important and distinctive angular measurements vary decidedly, and since a certain flexibility thus exists, the entrance of a different though similar mineral may take place without altering the angles beyond their ordinary limits. The extreme variation of axial dimensions which may take place is shown by the common and very well marked mineral calcite, the forms of which include 48 different rhombohedrons and 88 sealenohedrons, besides pyramids and prisms. If the extreme positive rhombohedrons were represented graphically on the same scale, one would be 112 times as long as the other.

Yet these extremes are so intimately connected by gradually progressive steps as to forbid any classification of them. - Many theories have been proposed to account for the exact forms assumed by minerals, but two of them will be sufficient to indicate the tendency of speculation. One is chemical. It supposes that the elementary atoms and molecules have definite forms, and that when two elements combine, their molecules take a form which is dependent on the forces that produce the combination. The introduction of a third element may produce a complete rearrangement of the molecules and an entirely new form. The other theory is based on physical laws. It has been suggested that minerals crystallizing in the isometric system may be com-posed of spherical molecules, that being the form which any body free to move must take when acted on equally in all directions. Minerals crystallizing in the other systems are made up of ellipsoidal molecules, and the form is tetragonal or rhombic, according as the lateral axes are conjugate axes or conjugate diameters of an ellipsoid. These axes and diameters are equal in all the systems except the triclinic, where they are unequal, and the vertical axis is at right angles to the other two in all but the monoclinic and triclinic systems.

The hexagonal form may be produced by an ellipsoidal molecule in which three conjugate diameters form the axes on which the faces are laid. These axes are called crystallogenic, to distinguish them from the ordinary crystallographic axes, which are entirely distinct. Molecules are supposed to be governed by the laws. of polarity, the opposite ends of the conjugate axes or diameters representing the north and south poles. By grouping them according to the known electrical laws, many of the remarkable compound forms can be imitated, and an interesting insight gained into the probable constitution of minerals. Local circumstances will sometimes alter the intensity of attraction between the molecules in favor of some one of the crystallogenic axes, and a distorted form will result. A more general modification of molecular relations produces secondary planes. What these local circumstances are is not known, but the character of the mother liquor, or of the solid matrix in which the mineral is formed, is certainly one of them.

Laboratory experiments prove this, and in nature we find aragonite assuming different modifications according as it is found in iron mines or in gypsum clays; minerals collected from one locality often present a general likeness, and may differ from the same species found in another region. - Since a crystal increases by successive additions to a minute molecular nucleus, any variations in the intensity of the uniting force must produce alternate zones of strong and weak attraction. These pulsations of the formative force are the cause of cleavage, which is due to the lessened tenacity of the mineral along those lines which represent the period of weak action during the pulsation.

III. Physical Characteristics. Fracture

Physical Characteristics. Fracture, taste, odor, polarization, electrical properties, and transparency are among the least decisive peculiarities of minerals. Streak is a very important character in all classes. Lustre is of great importance in distinguishing the two kinds, metallic and non-metallic minerals. The value of the other physical characters depends upon the kind of mineral under examination. Among those possessing metallic lustre, the hardness, specific gravity, color, and state of aggregation are far more serviceable than with those of non-metallic lustre. The origin of physical properties is unknown, but it is certain that some of them, as transparency, polarization, and refraction, depend upon the relations of the molecules toward light; lustre, color, and streak may have a similar origin, varied by the operation of the forces which formed the mineral. To these forces, tenacity, ductility, and state of aggregation may also probably bo ascribed. Some of the above mentioned characters, and also hardness and specific gravity, may be due partly or entirely to the state of chemical combination.

It has been shown that the superior hardness and specific gravity of the epidote group of minerals, as compared with the scapolite group, may be explained by supposing that the molecule of the former is more condensed than that of the latter. - Classification of Minerals. The explanations above given embody the leading principles upon which the numerous minerals found in nature are distinguished from each other and arranged in related groups. The unit in mineralogy is the species. A mineral species must have a definite composition and individual characteristics of form, sufficient to establish its difference from all others. The mode of occurrence may be gaseous, fluid, or solid; the nitrogen and oxygen of the atmosphere, water, and mercury are all native minerals, as well as the solid substances. But definiteness of composition is a necessary characteristic, and marks the difference between minerals and rocks. While the latter are composed of mineral substances, the indefiniteness of their constitution prevents their classification and description by the accurate methods known in mineralogy. Even in the latter science a certain latitude in composition is necessarily allowed, as minerals are seldom perfectly pure.

Elements foreign to those which properly compose the mineral are nearly always present, and when their amount is large in proportion to the whole, it may be a question whether a new species should be made. The tendency of the best authorities is to restrict the number of species as much as possible, and to describe the modifications, where the usual characteristics of the mineral are not much altered, as varieties. Thus under pyroxene Prof. Dana describes 21 varieties, and under amphibole 20. Tourmaline has already been cited as a case of extreme variation in chemical composition, and calcite in crystalline form, the variation in both cases being in remarkably well characterized species. In the fifth edition of Dana's "Mineralogy " (1868), 838 species are described, and the number of varieties is probably two or three times as great. The classification of these species is based upon chemical composition; compounds of one kind, as silicates or sulphides, being placed together and subdivided into groups having the same general symbol, or the same crystalline form, or some common physical character. The arrangement according^ to composition will be understood by referring to the table of elements given above.

Six general divisions are made: 1. Native elements, including any element in the pure state, and any compound of two elements in the same series and group. There are 20 elements known, forming 25 mineral species. Gold, silver, platinum, iridium, palladium, mercury, copper, lead, arsenic, antimony, bismuth, tellurium, sulphur, selenium, carbon, nitrogen, and oxygen are certainly found native; while iron, zinc, and tin, though reported, are somewhat doubtful, if meteoric iron is excluded as not having been subjected to terrestrial conditions. When elements from two or more groups are united in a mineral, we are brought to the study of compounds, which forms all the remaining part of mineralogy, including five divisions. 2. All compounds in which the negative element is taken from the arsenic or sulphur group (series II. in the table). This division therefore includes phosphides, arsenides, antimonides, bismuthides, sulphides, selenides, tellurides, and double compounds, as sulph-an-timonides, sulpho-bismuthides, etc.; in all, 110 species. 3. Compounds in which the negative element is taken from group A, series III., and therefore this division comprises all chlorides, bromides, and iodides, numbering 23 species. 4. Compounds containing the negative element of group B, series III., or fluorides, 13 in number. 5. Oxygen compounds, the negative element being taken from group C, series III. This division exceeds all others in the number of its species (587) and in the abundance of its minerals, which form probably more than nine tenths of the globe. 6. Those compounds of hydrogen and carbon which are called "organic," of which 73 species are recognized.

In addition to the above, more than 100 new species have been reported since 1868, and though some of these may not be sustained, the interest taken in mineralogy as a speculative science is rapidly extending our knowledge of minerals and the discovery of new species. - A general classification of species having been made according to chemical composition, as above explained, groups are formed, each of which contains minerals of one type. A mineral type includes species which closely resemble each other in crvstalline form, and have a related elementary composition. Thus eight similar compounds of protoxides and deutoxides are found to crystallize in the isometric system, and are all of the "spinel type." Crystallized minerals containing ferric anhydride assume either inclined or hemihedral forms, and therefore constitute a well marked type. Amorphous minerals are necessarily classed with those crystalline species which they resemble in composition, as their lack of definite form is looked upon not as a characteristic, but as the lack of one. This mode of ranking them does no violence to the theory held by some that they are formed from matter in the colloidal state. No uniform system of comparison has yet been discovered which will suit the requirements of all classes of minerals.

Each element appears to have a definite form, which it tends to assume under all circumstances; and if the strength of this tendency varies with each one, the form of any given species will either be that of some dominant element, or a compound one resulting from the interaction of all the substances contained in it. But nothing is known of such a scale of crys-tallographic forces except that, in the somewhat casual juxtapositions brought about by the present system of arrangement, we find different compounds, such as sulphates and carbonates, crystallized in different forms; while a species which is a compound of both these, a sulphato-carbonate, has the general form of the sulphates. From this fact it is concluded that sulphur has a more energetic formative power than carbon. An excellent and simple example of the principles on which mineral types and groups are arranged will be found in'Dana's "Mineralogy," fifth edition, p. 34, under the head of "Sulphides." - Nomenclature. Mineralogists have chosen the termination ite to characterize the names of their species.

Itis or ites was used by the Greeks and Romans for this purpose, and it was appended to some word signifying a quality, locality, or some other fact relating to the mineral, llcematites, for instance, referred to the red color of the powder, and syenites took its name from Syene in Egypt. Werner, in the last century, introduced the custom of naming minerals after persons, and, though much opposed for years, especially by French mineralogists, this is now the common usage. Its popularity does not spring so much from the desire to do honor to discoverers and distinguished men. as from the liability to error when an attempt is made to name a mineral from some supposed quality while the information about it is still imperfect. Many other terminations are in use, as ine, ane, ene, ase, age, ome, ate, etc.; but these have come down to us from former years. At present the rule is to use the termination ite, or if another is employed the latter must be applied to all minerals of the same class. A great advance in uniformity has been made by Dana, who undertook a thorough collation of the literature of the science, and applied the law of priority wherever it could be done without injury, thus restoring many old names.

While ite is used for minerals, yte is used for rock masses, which, to deserve the application of the word, should consist principally or entirely of the compact mineral. Thus dolerytc and pyroxenyte arc massive deposits of the minerals dolerite and pyroxene. - Mineralology is the name given to the study of the law's which govern the formation of minerals. While the chemist constantly endeavors to work with pure materials and to have but few elements present in the artificial production of mineral compounds, nature has undoubtedly formed many or all of the mineral species from sources in which a great number of elements were mixed. The circumstances under which ties., elements were brought together, their proportion, and the influences to which they were individually or collectively subjected af-crwanl, must have varied within very wide limits; and the fact that definite and unvarying upecies have been produced from heterogeneous compounds is proof of the operation of fixed and probably simple laws. On the other hand, the slight differences which are noticeable in the characteristic marks of a great many species are probably the traces of the different conditions under which the individuals of the species were formed.

The development of these laws, and of the forces which have modified them, forms the speculative part of mineralogical science, and makes the science itself an important factor both in the history of the earth and in the development of chemical knowledge. The present state of this knowledge will not permit a trustworthy statement of mineralological facts within the limits of this article. It is sufficient to point out some of the modes in which compounds may be formed. These are: 1, union of two gaseous elements; 2, union of one gaseous and one fluid or solid element; 3, union of two fluids; 4, union of one fluid and one solid; 5, combinations at a high temperature (igneous fluidity forming a matrix from which species separate on cooling); 6, combinations at a low temperature. - Artificial Minerals. By imitating these and other processes, many of the characteristic species may be reproduced, and the combinations always show themselves to be governed by the same laws that are discernible in the formation of true minerals. These artificial minerals mostly result from three sources: the study of chemical laws by experimental processes, the desire to produce gems by artificial means, and the casual formation of definite mineral compounds in metallurgical work.

Of the salts which result from chemical reactions, a great number have been found in nature. Of minerals used as gems, the ruby, aquamarine, garnet, topaz, spinel, chrysoberyl, apatite, and others have been produced, but not of a size large enough to make them useful as ornaments or their manufacture profitable. Metallurgical processes, where high temperatures and the action of gaseous substances are long continued, and where compounds of all degrees of fusibility are melted and chemically combined, are a fruitful source of artificial and very perfect minerals. A few furnace products have never been found in nature. While artificial minerals are apt to be less perfectly crystallized than the native specimens, they are also apt to be of simpler forms, and have sometimes served to determine the primitive angle when it could not be decided by natural specimens. - Historical. While the ancients were acquainted with a great number of minerals, and observed the existence of crystals and the importance of physical characters, their complete ignorance of all our modes of investigation prevented their obtaining any real knowledge of the distinctive species.

Stones of the most diverse composition, some minerals and some rocks, were grouped under one name, and it is frequently impossible to recognize from their description the minerals they knew. Theophrastus (315 B. C.) was the earliest writer on the subject, though other authors frequently referred to minerals as remedies, usually of the miraculous kind. Passing to the Christian era, we find Pliny writing on this subject in the 1st century, and Dios-corides in the same or the following; after which there is a blank until the 11th century, when Avicenna divided minerals into four classes, stones, salts, sulphurous or inflammable bodies, and earths. The "stones" were chiefly silicates, and rude as this classification is, it was not until long after chemical science had made its mark that anything very much superior was advanced, the principal improvement made in more than six centuries being the substitution of metals for "stones." Agricola (1543-50) wrote several works, studied the external characters of minerals, and based his arrangement upon those which are apparent to the senses. The alchemical studies of the succeeding centuries bore some fruit, both in the discovery of new species and in the addition of heating and fusion as modes of investigation.

Passing over Linnaeus (1735) and Wallerius (1747), who was the first to write a systematic descriptive work on this subject, we come to Oronstedt of Sweden, who in 1758 first pointed out the distinction between rocks and minerals which now enters into the fundamental definition of the latter. He based his system upon chemical properties. Rome de Lisle, in 1772-'83, made the first systematic effort to apply the principles of crystallography to the science, though Nicholas Steno had in the preceding century pointed out the fundamental fact that, with all their variations of form, the faces of crystals preserved the same angular relations; and later Gulielmini discovered that cleavage gave constant forms. Werner of Freiberg published in 1774 a work on the "External Characters of Minerals," in which he gave a much needed precision to the descriptive part of mineralogy, and retained the " natural affinity," or chemical composition, as the grand basis of classification, though the mode of carrying out the idea recalls Avicenna's work, seven centuries before.

Werner also made four classes, earths, salts, inflammables, and metals, the first named being further divided into silicious, argillaceous, calcareous, and talcose; but the silicious division was made to include nearly all the hard minerals, without regard to composition. It was under this form that mineralogy was introduced to English students by Kirwan in 1784. The science now began to receive constant and important additions, the three modes of determination which still remain criteria (crystalline form, chemical composition, and physical characters) being each in turn elevated to a position of dominant importance. In 1783 De Lisle published a second edition, in which crystallography received increased attention; and in 1801 Hauy's Traite de mineralogie appeared, in which crystallography was made the principal agent in the determination of mineral species. He rediscovered the importance of cleavage, and afforded a mathematical explanation of the phenomenon, referred the numerous secondary forms to a fundamental molecule of invariable shape, and reduced all crystal forms to six systems, based upon the following forms: 1, the regular octahedron; 2, the rhombohedron; 3, octahedron with a square base; 4, the octahedron with a rectangular base; 5, the prism with a symmetrical oblique base; and 0, the prism with an unsymmetrical oblique base.

By reference to the article Crystallography it will be seen that, though the details of his system have been changed, the axial differences recognized by him remain. In his system chemical composition and physical characters were entirely subordinate to crystallographic habits. He made four classes: 1, free acids; 2, substances which are metallic but do not present a metallic appearance, in- which were included the eight genera, lime, barytes, strontites, magnesia, alumina, potash, soda, and ammonia, together with the silicates; 3, metallic substances; 4, unmetallic combustible substances. In 1804 Mobs of Vienna published a description of a collection of minerals, in which the external characteristics alone were used to describe them. In 1820 he expanded his ideas into a "Natural History" system, the object of which was to group together all minerals which presented similar characters in regard to taste, lustre, gravity, streak, hardness, etc. No tests were used which destroyed the mineral, such as acids and fusion. Each group was gradually reduced by a process of comparison and exclusion to its individual members. This method was borrowed from other fields of science, and its nomenclature repeated the classes, orders, and genera of zoology and botany.

The system, though it has proved to be entirely unfitted to this science, did much good by requiring greater precision in description, bringing out many true relationships between species, and discarding unimportant distinctions which were flooding the science with false species. It is still used, with modifications, in mineralogical keys which are constructed for the use of young students, and persons little versed in the study. Mohs's classification included three classes: class 1 contained four orders, gas, water, acid, and salt, and included bodies which have taste, give no bituminous odor, and have a gravity below 3.8; class 2, bodies which have no taste, but are of specific gravity above 1.8; class 3, fluid bodies with bituminous odor, and tasteless bodies of specific gravity below 1 .8. This system was received with great favor, and not only held sway in Germany for 40 years, but extended into England and America. Two of the modes of determining minerals, crystalline form and physical characters, had now received the attention of able advocates, and were in rapid process of development by mineralogists throughout the world.

The third, that which stands at the head in the present system, is chemical composition, which received from Berzelius some time before 1816 (French edition, 1819) its first decisive impetus. That chemist looked upon mineralogy as properly a mere branch of his own favorite science. He explained mineral as he explained other compounds on the dualistio theory, according to which they were made up of an electro-positive and an electro-negative element or radical. His classification included two great groups, the first composed of native metals and binaries, not containing oxygen; and the second of electro-positive and electro-negative oxides, hydrates, silicates, alumina-silicates, tungstates, borates, carbonates, etc.; each acid, or each electro-negative element, having its own division as now. He introduced into the science the exact methods of chemistry, and urged the necessity of constant analysis, so that the existing mode of mineralogical study is known as the Berzelian, improved by the addition of crystallography and the special study of external marks. - While the science was thus receiving constant accessions in Germany and Sweden, the French mineralogists were also working out various schemes of classification.

Unable to produce a harmonious arrangement on any simple plan, they adopted a mixed system. Brongniart, in his Traite elements ire (1807) and Tableau des espdees mine-rales (1833), classified the earthy minerals according to the negative element, and the metallic ones according to the positive element, He had two grand divisions, the inorganic and organic. In the first were included 20 "min-eralizers," such as oxygen, hydrogen, and sulphur; the second class, metaux autopsides, contains true metals and their compounds; while the third class, metaux heteropsides, contains other bases and forms two orders, one of compounds without, and one of those with an acid. Beudant, in his Traite de mineralogie (1824), endeavored to restrict the classification of minerals to their chemical reactions. He formed three grand genera, based upon the characteristic negative clement. Gazolytes contained a negative element capable of forming stable gaseous compounds with oxygen, hydrogen, or fluoric acid, and included carbon, silicon, chlorine, etc. Leucolytes contained a negative element which does not form such stable gaseous compounds, but gives colorless solutions with acids. Chroicolytes, on the other hand, give colored solutions with acids.

Though this arrangement supplanted that of Hauy, the groupings of minerals formed under it were of the most heterogeneous character. Dufrenoy in 1844 published the first edition of a treatise in which a mixed system was again presented. He recognized natural groups in some of which the bases bore the important part, and in others the acids. In these mixed systems the bases are the real ground of classification, but the importance and number of the silicates, and the fact that the base plays a secondary part in most of them, compel an exception to be made in their favor in any scheme where the bases are made the characteristic elements. The French school has always been distinguished for eminence in crystallographic and physical researches, the latest development of which is to be seen in Descloizeaux's admirable investigations into the optical properties of minerals, by which the recognition of many obscure species has been greatly aided. The mixed classification of the French, however, has been rejected, partly for its incongruity and partly because the new chemical methods have been altogether in favor of the Berzelian mode. - In 1840 Gustav Rose of Berlin published a work on crystallography, in which the six crystalline systems formed the general divisions, in each of which the minerals were arranged in genera and species, according to their chemical composition.

In 1852 he published his Krystallo-chemisches Mineralsystem, in which the chemical composition is used both to determine the general arrangement and to fix the individual species, which are grouped into genera by their crystallographic characters. His method of arrangement was: 1, simple bodies; 2, compounds of sulphur, selenium, tellurium, arsenic, and antimony; 3, compounds of chlorine, fluorine, iodine, and bromine; 4, oxygen compounds. Rammelsberg, in several works, and especially in bis Handbuch der Mineralchemie, has paid great attention to the constitution of minerals, their relationships, the laws regulating their formation, and similar questions. K. G. Bischof, in his Lehrbueh der chemischen und physilcalischen Geologie, entered into the genesis of minerals, and, though his views have been frequently rebutted, he exerted a marked influence upon the progress of the science. Germany continues to be one of the most active fields for the advancement of this science. Tschermach, Leonhardt, Hessenberg, and others issue periodical reviews of progress, mineralogical magazines are published, and a great number of works on the science in all its branches are constantly issued.

The German school now probably includes a greater number of distinguished names than any other, though the science is rapidly advancing in all countries. - In the United States mineralogy had been but little cultivated before the beginning of the present century. A few collections of minerals had been brought from Europe, but the treatises of Kirwan and Jameson were almost the only works that could be consulted with reference to them, and very few were acquainted with these. In 1816 Prof. Parker Cleaveland of Bowdoin college published "An Elementary Treatise on Mineralogy and Geology," which was well received both in America and in Europe as a work of scientific importance, and particularly useful for the information it afforded respecting American minerals. The author, following the general plan of Brongniart at that time, sought to unite with the precise descriptive language of the system of Werner the chemical classification of the French mineralogists. His work was for many years highly popular, and indeed almost the only one in use by American mineralogists. A second edition appeared in 1822. Ten years afterward Prof. Charles U. Shepard of New Haven published the first part of his "Treatise on Mineralogy," and in 1835 the second part.

He adopted the arrangement of Mohs with little variation, making the natural history or external characters as far as possible the means of determining the species. He however appended a table in which the minerals were also arranged according to their chemical affinities. Francis Alger of Boston republished the then recent "Treatise on Mineralogy " prepared by Robert Allan from Phillips's "Mineralogy," enlarging it by numerous notices of American minerals and of recent discoveries. Like the last named work, it was particularly interesting for presenting many new facts in the development of the mineralogy of the United States. Prof. James I). Dana of New Haven commenced in 1837 the publication of his treatises upon mineralogy by the issue of the first edition of "A System of Mineralogy, including an extended Treatise upon Crystallography." Five editions of this work have been published. In those of 1837 and 1844 the natural history system of Mohs was extended and solidified, but in the third edition this was abandoned, and the author presented his work with a classification that claimed no inherent virtue but convenience. He however suggested a combination of the chemical and crystallographic methods, which in 1854 was embodied with alterations in a fourth edition.

During the 17 years covered by this work the views of the English school of chemists were steadily gaining ground, and when the fifth edition appeared in 1868 the "new chemistry" with its rational symbols and its new tenets had been established, and was used by the side of the old method in this work. The system employed is explained in the foregoing part of this article. No attempt is made to afford students a tabular arrangement by which the name of given specimens can be ascertained. The book bears to minerals a relation similar to that which a dictionary bears to words; it gives accurate definitions of them on a systematic plan. Great care has been taken with these definitions, and in fact Prof. Dana's method does not commence with the system, but with the species. When all the facts of composition, crystal form, and physical characters of a species are known, it can readily be placed with those of a similar kind, and minerals which resemble each other in these things necessarily form a group. Partial differences give rise to sub-groups, and resemblances between entire groups cause the formation of divisions. The system is therefore strictly rational. In other respects Dana's fifth edition is a great advance upon any previous publication in this branch of science.

He has adopted fixed rules for nomenclature and orthography, collated almost every work for synonymes, which are arranged in chronological order, and performed much similar work in a way that seems to leave nothing to be desired.