5.7" Gemmy, Twinned Calcite Crystal Cluster - Cumberland Mine
This is a beautiful, 5.7" long cluster of large, twinned calcite crystals from the Cumberland Mine in Smith Coutny, Tennessee. These large crystals are a light honey color and exhibit wonderful luster. There is some chipping on some of the large crystals, which is reflected in the much lower price.
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.