mineral

Naturally formed inorganic substance with a particular chemical composition and a regularly repeating internal structure. Either in their perfect crystalline form or otherwise, minerals are the constituents of rocks. In more general usage, a mineral is any substance economically valuable for mining (including coal and oil, despite their organic origins).

Mineral-forming processes include: melting of pre-existing rock and subsequent crystallization of a mineral to form igneous or volcanic rocks; weathering of rocks exposed at the land surface, with subsequent transport and grading by surface waters, ice, or wind to form sediments; and recrystallization through increasing temperature and pressure with depth to form metamorphic rocks. The transformation and recycling of the minerals of the Earth's outer layers is known as the rock cycle.

Minerals are usually classified as magmatic, sedimentary, or metamorphic. The magmatic minerals, in igneous rock, include the feldspars, quartz, pyroxenes, amphiboles, micas, and olivines that crystallize from silica-rich rock melts within the crust or from extruded lavas.

The most commonly occurring sedimentary minerals are either pure concentrates or mixtures of sand, clay minerals, and carbonates (chiefly calcite, aragonite, and dolomite).

Minerals typical of metamorphism include andalusite, cordierite, garnet, tremolite, lawsonite, pumpellyite, glaucophane, wollastonite, chlorite, micas, hornblende, staurolite, kyanite, and diopside.

Ice is also a mineral, the crystalline form of water, H2O.