MINERALOGY

A branch of physico-chemical science, which teaches the properties, composition, and relations of mineral bodies, and the art of distinguishing and describing them. " There is no branch of science," says Sir J. Herschel, " which presents so many points of contact with other departments of physical research, and serves as the connecting link between so many distant points of philosophical speculation, as this. To the geologist, the chemist, the optician, the crystallographer, it oflFers especially the very elements of their knowledge, and a field for many of their most curious and important inquiries; nor, with the exception of chemistry, is there any which has undergone more revolutions, or been exhibited in a greater variety of forms. To the ancients it could scarcely be said to be at all known; and, up to a comparatively recent period, nothing could be more imperfect than its descriptions, or more inartificial and unnatural than its cla ifications. The more important minerals in the arts, indeed, — those used for economical purposes, and those from which metals were extracted, — had a certain degree of attention paid to them for the ' sake of their utility and commercial value, and the precious stones for that of ornament; but until their crystalline forms were attentively observed, and shown to be determinate characters, on which dependence could be placed, no mineralogist could give any correct account of the real distinction between one mineral and another. It was only, however, when chemical analysis had acquired a certain degree of precision and universal applicability, that the importance of mineralogy as a science began to be recognized, and the connection between the external characters of a stone and its ingredient constituents brought into distinct notice." In the above quotation, the two characters of minerals upon which their cla ification is founded are adverted to, namely, their structure and their composition; and, pursuing these as their leading objects, mineralogists have of late discarded a number of other qualities upon which much stre was formerly laid, but which are so variable and indefinite as to be really of little value; such, for instance, as weight, colour, touch, and other sensible qualities, which often vary in different specimens of the same mineral. There are so many disadvantages belonging to any mineralogical arrangement founded exclusively on crystalline form, or on chemical composition, that, for all practical purposes, it is nece ary to blend the two; but since the chemical theory of definite proportionals, or, as it is commonly called, the atomic theory, has been shown to be applicable to the greater number of mineral combinations, the chemical arrangement of mineral substances has a umed a new and important aspect: it MINERALOGY. being of course nece ary, In describing a mineral, that its crystalline form and modifications should In all cases form an e ential part of such description, where at least it can be attained; for it must be recollected that there are many cases in which minerals do not occur crystallized, and where that characteristic, therefore, would be totally at fault. It has been well observed by Dr. Thomson (Si/stem of Chemistry, Part III., Introduction), " that if mineralogy were to be confined to mere crvstallized bodies, it would be divested of the greatest part of its utility; for a very great proportion of those minerals that are of the greatest utility to man, and which, therefore, it is peculiarly important to be able to distinguish from others, are seldom found in the state of regular crystals. How often do the ores of copper, tin, lead, and iron occur in an amorphous state? And were a mineralogist incapable of distinguishing them from each other, and from other minerals, except in the rare cases when they a ume a regularly crystallized form, his knowledge would be usele , as far as the important arts of mining and metallurgy are concerned." Mineralogical analysis, as connected with the atomic theory, has made no inconsiderable progre in the skilful and industrious hands of Berzelius; but it is still quite in its infancy as regards the foundation of a mineral arrangement; and, before it can be succe fully adopted as such, many new analyses, and much laborious revision of former researches, will be requisite. One of the latest authors on mineralogy, who has adopted an arrangement founded upon the chemical composition of minerals, is Dr. Thomas Thomson. He divides minerals into three cla es: — Cla I. Acid Bases. (Those bodies which become acids when combined with oxygen.) Genus I. Carbon II. Boron III. Silicon IV. Phosphorus. V. Sulphur VI. Selenium. VII. Tellurium VIII. Arsenic IX. Antimony X. Chromium. XI. Molybdenum XII. Tungstein. XIII. Columbium. XIV. Titanium. XV. Vanadium. Species. - II - I - 7 I. II, III. IV. V. VI. VII. VIII. IX. X. XI. XII. XIII. XIV. XV. XVI. XVII, Cla II. Alkaline Bases. Ammonia _. - Pota ium _ _ - Sodium ~ - - Lithium. Barium. _ _. Strontium _ - -. Calcium - Magnesium _ - -. Aluminum. 1. Pure, or combined with bases 2. Simple salts - _. 3. Double anhydrous salts 4. Double hydrous salts, soluble in water.... 5. Double, insoluble in water, and phosphates _. 6. Double hydrous aluminous silicates, or zeolites 7. Triple aluminous salts 8. Quadruple aluminous salts Glucinum... Yttrium... - Cerium _.. _ Zirconium.. _. Thorinum. - - -. Iron. 1. Uncombined, or united to a simple substance -. 2. Oxygen salts of iron Double ditto.. Triple ditto - 3. Sulphur salts of iron Manganese. 1. Combined with simple bodies 2. Simple oxygen salts 3. Double oxygen salts 4. Triple oxygen salts Nickel. 1. Combined with simple bodies 2. Oxygen salts - - 3. Sulphur salts - - Cobalt. 1. Combined with simple bodies 2. Oxygen salts.. 3. Sulphur salts... [s. 759]