Page:The American Cyclopædia (1879) Volume XI.djvu/603

 MINEEALOGY 585 of combination with oxygen. Its symbol is (iaFe + t/3Fe) 4 4, and it is therefore a binary compound. In franklinite the aFe is partially replaced by zinc and manganese in the alpha state, and the /3Fe is partially replaced by man- ganese in the beta state. The symbol then be- comes [KZn,Fe,Mn) + t/?Fe./Mn)] 4 O4. The a is not written, the protoxide state being under- stood 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 mineralo- gies, 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 spe- cies 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 ele- ments 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. Classifica- tion of the Elements. With the foregoing ex- planations the following table in which the elements are classified will be understood : CLASSIFICATION OF THE ELEMENTS. SEBIES I. SERIES II. j SEBIES III. A. Peritsads. A. Perissads. A. Perissads. Potassium, sodium, caesium, rubidium, lithium, thallium, hydrogen, Nitrogen, phosphorus, arsenic, anti- Chlorine. silver, gold. mony, bismuth, columbium, tan- Bromine. talum in the SK state, boron (?). Iodine. B. Artiads. B. Artiads. B. Perissad 1. Iron-aluminum group. 1. Sulphur group. (or Artiad). a. Iron sub-group : platinum, palladium, iridium, rhodium, osmium, ruthenium, copper, lead, mercury, iron, zinc, indium, cadmium, co- Sulphur, selenium, tellurium, mo- lybdenum ; also Fe, Cr, eMn, Fluorine. balt, nickel, manganese, chromium, uranium, tungsten, cerium, eV,eW. erbium, yttrium, glucinum, lanthanum, didymium, magnesium, calcium, strontium, barium ; also H 2, K,, Na, &c. b. Aluminum sub-group: aluminum (/3A1); also /3Fe, /SMn, /3Cr, j3 B, &c. C. Artiad. Oxygen. 2. Tin group. 2. Carbon-silicon group. Tin, titanium, zirconium, thorium ; also yH 2, -yFe, yMn, yCo, -yPb, Carbon, silicon ; also yS, ySe, yTe, yCu, &c. &c. 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 6, thus bring- ing 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 per- fect propriety be called the alpha, beta, &c., groups. Each group therefore includes not only its own leading elements, but also the a, /?, or y, &c., states of other elements ; and there- fore each group comprises a series of homoeo- 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 sys- tems. (See CRYSTALLOGRAPHY.) The atomic form seems to be different for the different elements ; and since the same element is some- times found crystallized in more than one sys- tem, 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 iso- metric system ; while allopalladium, which is also the native element in a pure state, is hex- agonal. 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 isomerisin. A great many of the compounds are identical in composition, but differ in form. Andalusite, fibrolite, and cyanite have the same composition, but crys- tallize in different systems, and have a different hardness and specific gravity ; and these differ- ences 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