Crocoite: Gemstones Information
The bright orange near transparent prismatic to monoclinic acicular crystals of chromite, PbCrO4, are occasionally cut but crystal groups are too highly prized by mineral collectors for many specimens to be faceted.The hardness is 2.5–3 and the SG in the range 5.9–6.1. The RI is 2.29, 2.36 and 2.66 for the alpha, beta and gamma rays respectively with a birefringence of 0.370, biaxial positive. A reddish to dark-brown fluorescence may sometimes be seen and thin sections may show an absorption band at 550 nm. Crocoite of facetable dimensions and quality occurs only at Dundas, Tasmania, where it is found in the oxidized zone of lead deposits in association with chromium-bearing rocks.