Pyrophyllite belongs to the montmorillonite group of minerals. It is remarkably similar to talc, which belongs to the same mineral family, except that magnesium is substituted for aluminium. In fact, chemical; tests are often requires to tell the two apart.
Its name comes from the Greek words “pyr” and “fullon” meaning fire and leaf respectively. The derivation stems from the fact that pyrophyllite breaks or exfoliates into leaves when fired to temperatures in excess of 800°C as a result of dehydration of its structure.
Pyrophyllite is quite abundant but not particularly common. It is found most commonly found in slate, phyllite and some schists.
The main deposits are found in China and Carolina in the USA. Other notable occurrences are located in Belgium, Switzerland, Mexico; Brazil, Sweden, Russia, and Japan.
Pyrophyllite has a sheet-like structure consisting of two silicate layers being sandwiched between gibbsite (Al(OH)3) layers.