calcite Very common, widespread, rock-forming carbonate mineral, one of two polymorphs of CaCO₃, the other being aragonite; sp. gr. 2.7; hardness 3; trigonal; usually colourless or white, but may be shades of yellow, grey, green, red, or even brown or black; white streak; vitreous lustre; crystals common, often tabular, prismatic, or rhombohedral, but fibrous aggregates and granular masses may also occur; cleavage perfect rhombohedral {101̄}; cleavage rhombs exhibit double refraction; a major constituent of calcareous sedimentary rocks, e.g. marbles. Calcite can be precipitated from sea water and is a common constituent of invertebrate shells, and late-stage hydrothermal solutions (see HYDROTHERMAL ACTIVITY) may precipitate calcite in cavities in some igneous rocks such as basalts. It is soluble in dilute hydrochloric acid. It is used as a flux, in cement-making and fertilizers, and as a building stone. See also CARBONATES.

cal·cite / ˈkalˌsīt/ • n. a white or colorless mineral consisting of calcium carbonate. It is a major constituent of sedimentary rocks, can occur in crystalline form, and may be deposited in caves to form stalactites and stalagmites.DERIVATIVES: cal·cit·ic / kalˈsitik/ adj.

calcite A very common form of calcium carbonate (CaCO₃) that is the principal ingredient of many sedimentary rocks (e.g. limestones, marble, and chalk).

calcite A very common form of calcium carbonate (CaCO₃) that is the principal ingredient of many sedimentary rocks (e.g. limestones, marble, and chalk).