This Specimen has been sold.
1.9" Gypsum on Dogtooth Calcite Crystal Cluster - China
This is a cluster of red-orange scalenohedral calcite crystals collected from China. Colorless gypsum var. selenite crystals encrust many of the calcite crystals.
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.
Selenite is a variety of gypsum, a soft sulfate mineral that is composed of calcium sulfate dihydrate (CaSO4 · H2O). When chemically pure, gypsum is transparent and colorless, however, impurities give the gypsum a diverse range of colors and formations. Desert rose, selenite and satin spar are just a few of the varieties of gypsum known to have formed though hydrothermal processes.