Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al₂Si₄O₁₀(OH)₂. It occurs in two forms (habits): crystalline folia and compact masses; distinct crystals are not known.

The folia have a pronounced pearly luster, 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 groups. This variety, when heated , exfoliates and swells up to many times its original volume, hence the name pyrophyllite, from the Greek pyro- (πυρο-, the combining form of πῦρ fire) and phyllos (a leaf), given by R. Hermann in 1829. The color of both varieties is white, pale green, greyish or yellowish; they are very soft (hardness of 1.0 to 1.5) and are greasy to the touch. The specific gravity is 2.65 - 2.85. The two varieties are thus very similar to talc.