mineral, inorganic substance occurring in nature, having a characteristic and homogeneous chemical composition, definite physical properties, and, usually, a definite crystalline form. A few of the minerals (e.g., carbon, arsenic, bismuth, antimony, gold, silver, copper, lead, mercury, platinum, and iron) are elements, but the vast majority are chemical compounds. A generalized formula can usually be assigned to each mineral that is a chemical compound, although sometimes one element in a mineral may be replaced by another without changing the species of the mineral (isomorphism). Minerals combine with each other to make up rocks, which, as distinguished from minerals, are of heterogeneous composition. Minerals may occur in the massive state when conditions for the formation of crystals are unfavorable. Among the important physical properties of minerals are specific gravity, hardness, cleavage, fracture, luster, color, transparency, streak, striations, tenacity, fusibility, heat conductivity, taste, odor, feel, magnetism, and electrical properties. Minerals originate by precipitation from solution, by the cooling and hardening of magmas, by the condensation of gases or gaseous action on country rock, and by metamorphism. Minerals in rocks are frequently replaced by other minerals through the action of water or gases (metasomatism). Minerals, especially the metals, are of great economic importance to a highly industrialized civilization, entering into the composition of many manufactured articles. Many minerals which would otherwise be of no economic significance are highly valued as gems (see gem). Mineralogy, a branch of geology, is the science of minerals.

See J. L. Gillson, Industrial Minerals and Rocks (1960); C. S. Hurlbut, Jr., Minerals and Man (1968); B. Mason and L. G. Berry, Elements of Mineralogy (1968); C. J. Morrissey, ed., Mineral Specimens (1968); J. D. Dana, Manual of Mineralogy (18th ed., rev. by C. S. Hurlbut, Jr., 1971); K. Frye, ed., The Encyclopedia of Mineralogy (1982).

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