Anhydrite: Gemstone Information
Anhydrite is CaSO4 and forms tabular or equant crystals of the orthorhombic system with hardness 3.5 and SG 2.95–2.96. There is one direction of perfect cleavage. Transparent to translucent material may be colourless to light pink, pale blue to violet. Anhydrite is usually formed by the dehydration of gypsum. Good cleavages in pale purple have come from the Simplon tunnel, Valais, Switzerland and some material has been fashioned; similar specimens have come from the Faraday mine,Bancroft, Ontario, Canada. Large and attractive blue masses have come from Naica, Chihuahua, Mexico. Some German anhydrite may show a red fluorescence under LWUV.