1.9" Rosasite, Aurichalcite and Calcite Crystal Association - Utah
This colorful specimen contains deep blue-green colored botryoidal rosasite formations and aurichalcite, most of which is enshrouded in a thin layer of transparent calcite crystals. It was collected from the Hidden Treasure Mine in the Ophir District of Utah, a location that's well known for its zinc and copper mineral deposits.
Rosasite is a secondary mineral that forms in oxidation zones of copper-zinc deposits, generally forming a fibrous botryoidal sphere that can appear vitreous and silky. While typically featuring a blue-green color, colorless specimens are not unheard of. The chemical formula of rosasite is CuZnCO3(OH)2.
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.