Al2Si2O5OH4

Al2Si2O5(OH)4, commonly known as kaolinite, is a clay mineral in the phyllosilicate group. It is a 1:1 layer silicate consisting of silicate tetrahedra linked to aluminum-centered octahedra; the layers are held together by hydrogen bonds, resulting in a non-expanding structure.

Kaolinite forms by chemical weathering of feldspar and other aluminosilicate minerals under tropical to temperate climates. It occurs in soils and sedimentary rocks and is widely distributed in deposits around the world. It is commonly found with other clay minerals such as illite and goethite.

In terms of properties, kaolinite is white to cream in color with an earthy luster and a microscopic plate-like habit. It has a Mohs hardness of about 2 to 2.5 and a specific gravity around 2.16 to 2.65. It is largely insoluble in water and is relatively unreactive, exhibiting little swelling and a low cation-exchange capacity.

Kaolinite is best known for its industrial use as kaolin, a primary component of porcelain and fine ceramics. It is also utilized as a filler and coating in paper production, in paints and plastics, and in cosmetics and pharmaceuticals as an adsorbent and whitening agent.

Etymology-wise, kaolinite is named after Gaoling (Kao-ling) hill in Jingdezhen, China, from which the mineral was historically extracted. The term kaolin refers to the industrial clay material derived from kaolinite.