kaolin

Kaolin, also known as china clay, is a white, soft clay mineral within the group of industrial minerals. It is a hydrated aluminum silicate with the idealized formula Al2Si2O5(OH)4. Kaolinite consists of microcrystalline, platy particles that provide high brightness and a fine particle size. The mineral is chemically inert under many conditions and has a relatively low shrink-swell capacity, which makes it valuable in ceramics and as a filler.

Kaolin forms by chemical weathering of feldspar-rich rocks such as granite and feldspathic sandstone in tropical and subtropical climates. It occurs in both sedimentary and residual deposits. The name kaolin derives from Gaoling (Kaoling), a Chinese village near Jingdezhen, historically linked to porcelain production.

Raw kaolin is mined and then processed by washing, drying, and milling to produce standard particle sizes. In many applications, calcination is used to produce modified forms: calcined kaolin increases hardness and whiteness, while higher-temperature processing yields metakaolin, a reactive aluminosilicate used as a supplementary cementitious material and additive in polymers. The degree of calcination affects brightness, refractoriness, and rheology.

Main applications include whiteware ceramics such as porcelain and fine china; paper coating and filler to improve gloss and brightness; paints and plastics as a filler; and cosmetics and pharmaceuticals as a smooth, inert excipient.

Kaolin is valued for its whiteness, inertness, and fine particle size. It can contain trace impurities such as quartz or mica, which affect brightness and handling. Dust can pose health risks if inhaled; mining and processing follow standard occupational safety and dust controls. Environmental considerations include water usage and waste management in mining operations.