Kaolinite. Kaolinite ( /ˈkeɪəlɪnaɪt/) is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5 ( OH) 4. It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO 4) linked through oxygen atoms to one octahedral sheet of alumina (AlO 6) octahedra.