Dioptase: Gemstones Information
Dioptase is copper silicate CuSiO2 (OH)2 and forms prismatic or rhombo-hedral crystals of the trigonal system. Due to the low hardness of 5 and the perfect cleavage, faceted stones are comparatively rare; crystal groups on the other hand may command high prices. The green is very strong and bright even when compared to the perhaps more subtle green of emerald. Many specimens are translucent at best.The SG ranges from 3.28 to 3.35 and the RIs are 1.644–1.658 for the ordinary ray and 1.697–1.709 for the extraordinary ray, uniaxial positive.The DR is about 0.053. The absorption spectrum shows only a broad band in the yellow and green centred at about 550 nm and there is a strong absorption in the blue and violet.Dioptase is found in the oxidized zones of some copper deposits. Some of the best crystallized specimens of fine green dioptase are found near Altyn-Tyube, east of Karaganda, Khirghiz Steppe, Kazakhstan, and in the areas of Renéville, Mindouli and Pimbi, Congo Republic. Fine crystals are also found at Tsumeb, Namibia.