Kaolinite

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Kaolin redirects here. For the band, see Kaolin (band).

Image:KaolinUSGOV.jpg Image:KaoliniteUSGOV.jpg

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 molecules to one octahedral sheet of alumina octahedra. Rocks that are rich in kaolinite are known as china clay or kaolin (Template:Zh-cp), named after Gaoling ("High Hill") in Jingde Town, Jiangxi, China. It was first described as a mineral species in 1867 for an occurrence in the Jari River basin of Brazil [1].

It is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicates, 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.

Kaolinite is one of the most common minerals; it is mined in Brazil, France, Britain, Germany, India, Australia, Japan , China, and the southeastern U.S. states of Georgia, Florida, and, to a lesser extent, South Carolina. Due to its extremely fine nature (finer than silt), it is mixed with water and transported in tanks as a liquid slurry. It is used in ceramics, medicine, bricks, paper, as a food additive, in toothpaste, 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. The largest use is in the production of paper, as it is a key ingredient in creating 'glossy' paper (but calcium carbonate, a cheaper substitute, is slowly taking over this function).

Natural kaolinite usually contains small amounts of uranium and thorium, and is therefore useful in radiological dating. While a single magazine made using kaolinite 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.

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