4.1" Amber-Yellow Calcite Crystal Cluster - Highly Fluorescent!
This is 4.1" wide, amber-colored calcite crystal cluster that was collected from the Kjørholt mines near Porsgrunn, Norway. Under both short and long-wave UV, these crystals have a magnificent fluorescence. Under short-wave UV, the fluorescence is white, while under long-wave UV, the crystals exhibit a white-green fluorescence.
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.