Carnotite

Carnotite is a hydrous potassium uranyl vanadate mineral with the chemical formula K2(UO2)2(VO4)2·3H2O. It forms as a secondary mineral in oxidized faces of uraniferous sandstone and shales and is widely recognized as a principal ore of both uranium and vanadium in arid, uranium-bearing districts.

Physical properties: It is typically yellow to olive-yellow, occurring as tabular or plate-like crystals, but more commonly as earthy masses and crusts. It has a resinous to earthy luster, Mohs hardness about 2–3, and a specific gravity around 4.0–4.6. It is radioactive and should be handled with care.

Geographic occurrence and paragenesis: Carnotite is associated with other uranium-vanadium minerals and weathering products in oxidized zones of sandstone deposits. Classic localities include the sandstone basins of the Colorado Plateau in the United States; additional deposits have been reported in Namibia and other vanadium-rich terranes.

Economic and historical significance: In the late 19th and early 20th centuries carnotite deposits supplied uranium and vanadium for early nuclear and steel industries; mining declined as alternate uranium sources were developed; it remains an important indicator mineral in exploration and a notable historical ore.