Lustrous, .6" Yellow Apatite Crystal on Calcite - Morocco
This specimen contains a greenish-yellow apatite crystal that formed from a calcite crystal. This crystal cluster was collected from Imilchil, Morocco.
Apatite's bright, lustrous crystals form hexagonal shapes with off-center terminations. They are found in vugs (small cavities in rock), often associated with quartz and calcite. Many crystals are around an inch in length, though larger crystals up to about 4 inches long have been found.
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. Its fracture is conchoidal, but difficult to obtain.