Kaolinite is a clay mineral with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra. Rocks that are rich in kaolinite are known as china clay or kaolin (Simplified Chinese: ???; pinyin: Gaoling tu), named after Gaoling ("High Hill") in Jingdezhen, Jiangxi province, China and were traditionally used in the manufacture of porcelain. It was first described as a mineral species in 1867 for an occurrence in the Jari River basin of Brazil.
Kaolinite has a low shrink-swell capacity and a low cation exchange capacity (1-15 meq/100g.)
It is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world, it is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow or light orange colours. Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, USA. Sandersville, a small town in Washington County, Georgia, holds an annual kaolin festival every year. Sandersville has huge kaolin deposits throughout the town and the surrounding areas. The town is based on the kaolin industry.
Kaolinite is one of the most common minerals; it is mined, as kaolin, in Brazil, France, Britain, Germany, India, Australia, Korea , the People's Republic of China, and the southeastern U.S. states of Georgia, Florida, and, to a lesser extent, South Carolina. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry. It is used in ceramics, medicine, bricks, coated paper, as a food additive, in toothpaste, as a light diffusing material in white incandescent light bulbs, and in cosmetics. A recent use is as a specially formulated spray applied to fruits, vegetables, and other vegetation to repel or deter insect damage. A traditional use is to soothe an upset stomach, similar to the way parrots (and later, humans) in South America originally use it, and until the early 1990s, it was the active substance of Kaopectate. The largest use is in the production of paper, as it is a key ingredient in creating "glossy" paper (but calcium carbonate, an alternative material, is competing in this function).
Kaolinite can contain very small traces of uranium and thorium, and is therefore useful in radiological dating. While a single magazine made using kaolin does not contain enough radioactive material to be detected by a security-oriented monitor, this does result in truckloads of high end glossy paper occasionally tripping an overly-sensitive radiation monitor.
The crystallography of kaolinite played a role in Linus Pauling's work on the nature of the chemical bond.