This Specimen has been sold.
2.5" Biotite, Diopside & Calcite Association - Afghanistan
This is a 2.5" wide association of yellow-green diopside crystals, biotite and calcite. This mineral association was collected from Khogyani, Afghanistan and is in great condition.
Diopside is a pyroxene mineral with the chemical formula MgCaSi₂O₆. It is often found as small green crystals within metamorphic and igneous rocks, though it can vary in color including yellow, brown and black crystals. It is an important indicator rock when searching for deep-source volcanic pipes that may or may not contain diamonds. Geologists that are searching for these pipes often look for diopside crystal fragments since they form in nearly the same atmospheric conditions and locations as diamonds. Diopside crystals with deep green coloration are known as chrome diopside.
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.