Calcite

Calcite, soft mineral, consisting of calcium carbonate (CaCO₃), found mainly in limestone. Most stalagmites and stalactites are made of calcite. Calcite is usually white, but impurities may give it other colors. Very pure calcite, such as Iceland spar, is often transparent and causes double refraction, so that objects seen through it appear double, making it useful in some optical instruments. Other forms of calcite include marble and Oriental alabaster. Calcite is used to make lime, cement, and fertilizers.

See also: Calcium carbonate; Lime.