Pyrophyllite: Gemstone Information
Pyrophyllite is Al2Si4O10(OH)2 and forms compact translucent or opaque spherulitic aggregates of acicular radiating crystals or foliated laminae in the monoclinic or triclinic systems. There is one direction of perfect cleavage and the lustre is greasy or pearly. Colours are white or pale shades of blue, yellow or green. The hardness is 1–2 and the SG 2.65–2.90. The RI for the alpha, beta and gamma rays is 1.534–1.556,1.586–1.589, 1.596–1.601, biaxial negative with birefringence 0.050.Pyrophyllite occurs in hydrothermal veins and in deposits of schistose rocks.The ornamental interest in pyrophyllite arises from its similarity to soapstone (q.v.) from which it may be distinguished by chemical tests for aluminium whose presence indicates pyrophyllite. Large crystals have been found in the Ibitiara area of Bahia, Brazil. China produces materials suitable for carvings.