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Concept
Kaolinite
Summary
Kaolinite (ˈkeɪ.ələˌnaɪt,_-lɪ- ) is a clay mineral, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina () octahedra.
Kaolinite is a soft, earthy, usually white, mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. It has a low shrink–swell capacity and a low cation-exchange capacity (1–15 meq/100 g).
Rocks that are rich in kaolinite, and halloysite, are known as kaolin (ˈkeɪ.əlᵻn) or china clay. In many parts of the world kaolin is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lower concentrations yield white, yellow, or light orange colors. Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, United States.
Kaolin is an important raw material in many industries and applications. Commercial grades of kaolin are supplied and transported as powder, lumps, semi-dried noodle or slurry. Global production of kaolin in 2021 was estimated to be 45 million tonnes, with a total market value of $US4.24 billion.
The name kaolin is derived from Gaoling (), a Chinese village near Jingdezhen in southeastern China's Jiangxi Province. The name entered English in 1727 from the French version of the word: kaolin, following François Xavier d'Entrecolles's reports on the making of Jingdezhen porcelain.
Kaolin is occasionally referred to by the antiquated term lithomarge, from the Ancient Greek litho- and Latin marga, meaning 'stone of marl'; presently the name lithomarge can refer to a compacted, massive form of kaolin.
The chemical formula for kaolinite as used in mineralogy is , however, in ceramics applications the formula is typically written in terms of oxides, thus the formula for kaolinite is .
Compared with other clay minerals, kaolinite is chemically and structurally simple. It is described as a 1:1 or TO clay mineral because its crystals consist of stacked TO layers.
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