Chemically kaolin is identified by the formulae Al2Si2O5(OH)4, or as Al2O3·2SiO2·2H2O. Therefore Kaolin is an alumina-silicate as indicated by the formulae. Structurally kaolin is a platy mineral. Repeat units of Si-tetrahedron form the Si sheet; whereas repeat units of Al-octahedron form the Al-sheet. The tetrahedron and octahedron sheets from 1:1 plate formation to form kaolin.