Mineral (chemistry)

Mineral (chemistry), in general, any naturally occurring chemical element or compound, but in mineralogy and geology, chemical elements and compounds that have been formed through inorganic processes. Petroleum and coal, which are formed by the decomposition of organic matter, are not minerals in the strict sense. More than 3000 mineral species are known, most of which are characterized by definite chemical composition, crystalline structure, and physical properties. They are classified primarily by chemical composition, crystal class, hardness, and appearance (color, luster, and opacity). Mineral species are, as a rule, limited to solid substances, the only liquids being metallic mercury and water. All the rocks forming the earth's crust consist of minerals. Metalliferous minerals of economic value, which are mined for their metals, are known as ores. See Crystal.