Powellite: Gemstone Information
Powellite is CaMoO4 and is isostructural with scheelite with which it forms a series. Powellite occurs as transparent to translucent straw yellow, greenish yellow, greenish blue or blue dipyramidal crystals of the tetragonal system; the lustre is characteristically greasy or subadamantine and the hardness 3.5–4. The SG is near 4.23 and the RI of the ordinary and extraordinary rays is 1.974 and 1.984, uniaxial positive.Under both forms of UV, specimens may fluoresce yellowish white to golden yellow. Powellite occurs as an uncommon secondary mineral in the oxidation zone of molybdenum-bearing hydrothermal mineral deposits. Facetable material is rare as crystals are usually small but some specimens from the Isle Royal, Calumet and Hecla mines, Houghton County, Michigan, USA, have been fashioned. Notable crystals are found at Pandulena Hill, Nasik, Maharashtra, India.