Calcite is a carbonate mineral and is among the most widely distributed minerals on the Earth's surface.
The name calcite is derived from the Greek word chalix, meaning "lime."
Single, transparent crystals of calcite display an optical property called birefringence or double refraction.
Usually white or colorless, calcite can also be found in shades of gray, red, yellow, green, blue, violet, brown, or black, when the mineral is charged with various impurities.
One of its well-known properties is called birefringence or double refraction, because of which objects viewed through a clear piece of calcite appear doubled.
When exposed to water, vaterite converts to calcite (at low temperature) or aragonite (at about 60°C).
Calcite is often the primary constituent of the shells of marine organisms.
Calcite represents the stable form of calcium carbonate.
Calcite (especially as limestone) is an important building stone and a raw material for the manufacture of lime (calcium oxide), slaked lime (calcium hydroxide), cements, and mortars.
Crystals of calcite are hexagonal-rhombohedral, though actual calcite rhombohedrons are rare in nature.