A crystalline form of calcium carbonate (CaCO3). Calcite is one of the most common and widespread minerals. It crystallizes in the rhombohedral system, is usually colorless or white, and has a hardness of 3 on the Mho scale. It has the property of double refraction, which is apparent in the transparent variety of calcite known as Iceland spar.
Calcite is an important rock-forming mineral and a major constituent of limestones, marbles, and carbonatites.