PYROPHYLLITE   Pyrophyllite is a phyllosilicate mineral species belonging to the clay family and composed of aluminium silicate hydroxide: AlSi2O5OH.   Pyrophyllite occurs in phyllite and schistose rocks, often associated with kyanite, of which it is an alteration product. Pale green foliated masses, very like talc in appearance, are found at Beresovsk near Ekaterinburg in the Urals, and at Zermatt in Switzerland.   At Ashapura China Clay, pyrophyllite is available in powder form.