2.9" Manganoan Calcite and Kutnohorite Association - Fluorescent!
This is a 2.9" wide association of light-pink, manganese baring calcite (manganoan calcite) and kutnohorite. It was collected from Wessels Mine in the Kalahari manganese fields of South Africa. Under both short and long-wave UV light, the calcite fluoresces a vibrant red-pink color.
Manganoan calcite, also known as manganocalcite is a pink, manganese rich variety of calcite with a chemical composition of (Ca,Mn)CO3. It crystallizes in a trigonal crystal system and forms rhombohedral or scalenohedral crystals. These crystals tend to display a pink color of which intensity can range anywhere from a pinkish-salmon to a hot pink. Often this variety of calcite will exhibit fluorescent properties.
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.
Kutnohorite is a rare calcium manganese carbonate with the chemical formula Ca(Mn,Mg,Fe)(CO3)2. It is common for magnesium and/or iron to substitute themselves for manganese, resulting in different colors or crystal shapes.