1.9" Dioptase and Calcite Association - Tantara Mine, Congo

This is a 1.9" wide association of calcite and dioptase crystals that was collected from the Tantara Mine in the Democratic Republic of Congo.

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.

Dioptase is an uncommon mineral found mostly in desert regions where it forms as a secondary mineral in the oxidized zone of copper sulfide mineral deposits. This copper based mineral forms small rhombohedral crystals, typically less than 0.75 cm in length.
It is popular with mineral collectors due to it's vibrant color and it is occasionally cut into small emerald-like gems.
Calcite & Dioptase
Tantara Mine, Shinkolobwe, Katanga Province, DR Congo
1.9" wide