Cryolite: Gemstones Information
Colourless transparent monoclinic crystals of cryolite, Na3AlF6, have occasionally been cut despite their softness and hazy appearance. The hardness is 2.5, the SG 2.97. The RI is 1.338, 1.338 and 1.339 for the alpha, beta and gamma rays, with a birefringence of 0.001, biaxial positive. Monoclinic crystals are short prismatic or pseudocubic. Cryolite occurs in some granite pegmatites, in topaz-bearing, fluorine-rich rhyolites and elsewhere.Fashioned material is most likely to have originated at Ivigtut, Greenland.