MINERALOGY (Fr. miner, to dig, mine; Gael. meinn; Wel. mwn, ore, mine), the science which treats of minerals. But it does not embrace all that relates to the mineral kingdom. Simple mineralsalone, or homogeneous mineral substances, are regarded as the subjects of mineralogy; rocks formed by the aggregation of simple minerals, and their relations to each other, are the subjects of geology (q.v.). This limitation of the term mineralogy is comparatively recent. Geology or geog,nosy was formerly included in it. The arrangement and description of simple minerals according to their external charac ters has been called by Werner and others oryetognosy, but the term has fortunate/3' fallen into disuse. Nor is the study of mere external characters sufficient in mineralogy, The chemical composition of minerals equally demands attention. In the classification of minerals, some mineralogists, as Molts and Jameson, have regarded only- the external characters, and some, as Berzelius, only the chemical composition; but the results have been unsatisfactory', and the present tendency is in favor of a system which seeks to. constitute natural crroups by having regard to both.
Some mineralsbeing of great use, and others highly valued for their beauty, have received much attention from the earliest ages. But the ancient naturalists describe few minerals. The first attempt at scientific mineralogy was by George Agricola in the lfith century. The systems of the Swedes Wallerins and Cronstedt, in the latter half of the 18th c., were the first worthy of the name. That of Werner followed, and was exten sively adopted. The discoveries of Hauy in crystallography, and the progress of chemistry, gave mineralogy a new character; and then sprung up two schools of mineralogists, one resting chiefly on external characters, and the other on chemical composition.
The chemical classification of minerals is rendered difficult by the endless variety of combination and proportion in the elements of which they are composed, the presence of substances not essential to the mineral, and yet more or less affecting its characters, and the frequent impossibility of determining what is to be deemed essential, and what accidental. Chemical purity is almost never found in nature. Even tile purest diamond, when burned, leaves some traces of ash; and the various colors of diamond, quartz, and other minerals are due to the presence of substances which are often in so small quantity as not to affect their crystalline forms or other physical properties. Again, some minerals of identical chemical composition differ in their crystallization, so that an arrangeinent founded upon it would separate them too widely. There are also many minerals which
are often found in an uncrystallized state, and others which arc always so. In the arrano-ement of minerals into natural groups, their chemical composition, although not alonjto be regarded, is of the first importance, so that the place of a new mineral in the system can never be determined without analysis; and in determining the nature of a mineral, chemical tests, such as the application of acids, are continually resorted to. It is also necessary to know its specific gravity, and how it is acted upon both by a tnoderatc heat and by the blowpipe. An examination of the crystalline forms, with measurement of the angles of the crystals, is often sufficient to distinguish minerals which have otherwise much resemblance. The cleavage of crvstals is also important, a readiness to split in planes parallel to certain of their faces only, by which the primikve form of the crystal may be ascertained. Minerals not crystallized exhibit important varities of structure, as laminated, fibrous, granular, etc. Certain peculiarities of form are also frequently characteristic of uncrystallized minerals, as mamillary, botryoidal, etc. Minerals exhibit, when broken, very different kinds of fra,cture, as even, conchoidat, splintery, etc. Opaqueness, translucency, mid transparency are more or less characteristic of different kinds: electric and magnetic properties demand attention; and very impor tant characters are derived from luster, which in some minerals is metallk, in others semi-metallie, in others pearly, vitreous, etc. Caor is not generally of much importance, but in some minerals it very characteristic. Hardness and tenacity are vei7 important, and are of all various degrees. A few fluid, and even a few gaseous substances, are included in mineralogical systems. Unctuosity and other peculiarities to be a.scertained by the touch, are very characteristic of some minerals; peculiarities of taste and smell belong to others.
Mineralogy has very important relations with geology, which cannot be studied without regard to the mineral constituents of rocks. The mineral composition of soils greatly affects vegetation and agriculture. The economical uses of minerals are also very important and various. It is enough merely to allude to coal, lime, salt, and the metallic ores. Naphtha, petroleum, bitumen, asphalt, etc., are of well-known utility; a,nd a high value has always been attached to gems and other ornamental stones.