a very soft, greasy, monoclinic mineral, AlSiO(OH), that is similar to talc in structure, used as a lubricant and in making rubber, soap, etc.; hydrous aluminum silicate
See pyrophyllite in American Heritage Dictionary 4
(pīˌrō-fĭlˈītˌ, pī-rŏfˈə-lītˌ)
noun
A silvery white or pale green aluminum silicate mineral, Al2Si4O10(OH)2, occurring naturally in soft compact masses.