Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide .It occurs in two more or less distinct varieties, namely, as crystalline folia and as compact masses distinct crystals are not known.The folia have a pronounced pearly lustre, owing to the presence of a perfect cleavage parallel to their surfaces. They are flexible but not elastic and are usually arranged radially in fan- like or spherical group. This variety, when heated before the blowpipe , exfoliates and swells up to many times its original volume, hence the name pyrophyllite, from Greek pyros and phyllos.