5.4" Free-Standing, Polished Brown Calcite

This brown calcite was mined from the Norcross-Madagascar brown calcite quarry. This type of calcite likely occurred as a massive conglomerate, formed from mineral-rich water solidifying after accumulation as flowstone and/or through precipitative processes.

Calcite, CaCO3, is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, and prisms. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form. Its fracture is conchoidal, but difficult to obtain.