Pyrophyllite (Al 2[Si 4O 10](OH) 2 or Al 2O 3·4SiO 2·H 2O) is an aluminum silicate with a 2:1-type (TOT-type) dioctahedral layer structure. In the classification of mineral crystal chemistry, pyrophyllite belongs to the silicate class, the layer-structured silicate subclass, and the talc group. In the structural-functional classification of mineral raw materials in mineral material science, pyrophyllite belongs to the category of two-dimensional structural minerals and the subcategory of functional minerals.