Pyrophyllite - Wikipedia. Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al 2 Si 4 O 10 (OH) 2.It occurs in two forms (): 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 ...
