2.3" Aurichalcite and Calcite Association - Utah
This colorful specimen contains an association of colorless calcite crystals and sky-blue fibrous aurichalcite. 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.
Aurichalcite is a secondary mineral that forms in the oxidation zones of copper and zinc ore deposits. It has the chemical formula (Zn,Cu)5(CO3)2(OH)6 and often forms as radiating acicular blue-green crystals and linings along cavity walls.
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.