Covellite: Gemstones Information
Covellite is CuS and forms notably iridescent opaque masses in the hexagonal system with a highly perfect cleavage in one direction, hness 1.5–2 and SG 4.6–4.7. The RI for the ordinary and extraordinary rays is 1.45 and 2.62, uniaxial positive with high birefringence (not of importance to gemmologists). Covellite occurs in the secondary enrichment zones of copper deposits. Ornamental material, sometimes large,is found at a number of copper mines in the US. Fine crystals have been found in the primary ore at Butte, Silver Bow County, Montana; also at Kennecott, Alaska. Large crystals have also been found at the Calabona mine, Alghero, Sardinia, Italy.