4.6" Fluorescent, Yellow Calcite Crystal Cluster - South Dakota
This is a cluster of yellow calcite crystals that was collected from Meade County, South Dakota. Under long wave and short wave UV, these crystals react by fluorescing orange-yellow (long wave UV) and white-yellow (short wave UV).
Elk Creek, South Dakota is renown for producing these calcite and barite specimens. The barite crystals collected from here are considered some of the nicest specimens around the world and can sell for thousands of dollars. These mineral specimens form as fossiliferous septarian, calcareous concretions that erode out of the Gregory Member of the Pierre Shale. These concretions have to be carefully opened with specialized diamond saws. If opened incorrectly or too hastily, the calcite and world class barite crystals can be damaged easily.
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.