Pyrophyllite is a rare phyllosilicate mineral, an aluminum silicate hydroxide (Al2Si4O10(OH)2) It occurs either as flakes more or less similar to muscovite or as compact radial-acicular (needle like) masses, with distinct crystals not known. The folia have a pearly luster, and are usually arranged in radial fan-like or spherical groups, in off-white to orange red hues. Pyrophyllite occurs in phyllite and schistose rocks, often associated with kyanite, of which it is an alteration product. It also occurs as hydrothermal deposits, and is then an alteration product of feldspar. Pyrophyllite has been mined as a substitute for talcum. This sample from Graves Mountain in Georgia, USA, actual width is 110 mm.