Soapstone: Gemstones Information
Soapstone, Mg3Si4O10(OH)2, is the popular name for ornamental varieties of talc, which forms triclinic or monoclinic crystals and finegrained compact masses with a characteristic soapy feel, one direction of perfect cleavage and hardness 1 when more or less pure; the SG is 2.20–2.83. The colour ranges from light to dark green to brown, white or colourless. The RI for the alpha, beta and gamma rays is 1.539–1.550,1.589–1.594, 1.589–1.600, biaxial negative with birefringence 0.039. In practice the massive material will show a single reading near 1.54 on the refractometer.Soapstone occurs in talc-rich schists from the hydrothermal alteration of mafic rocks. Material used for carvings may have come from a number of sources including Egypt (ancient deposits) and the European Alps.