Kaolin is used in ceramics, medicine, coated paper, as a food additive, in toothpaste, as a light diffusing material in white incandescent light bulbs, and in cosmetics. It is generally the main component in porcelain.
It is also used in paint to extend titanium dioxide (TiO2) and modify gloss levels; in rubber for semi-reinforcing properties; and in adhesives to modify rheology.
Kaolin was long used in the production of common smoking pipes in Europe and Asia.
The largest use is in the production of paper, including ensuring the gloss on some grades of paper. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.
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.
Kaolinite has also seen some use in organic farming, as a spray applied to crops to deter insect damage, and in the case of apples, to prevent sun scald.
In April 2008, the US Naval Medical Research Institute announced the successful use of a Kaolinite-derived aluminosilicate nanoparticle infusion in traditional gauze, known commercially as QuikClot Combat Gauze.
When heated to between 650 and 900 °C kaolinite dehydroxylates to form metakaolin. According to the American National Precast Concrete Association this is a supplementary cementitious material (SCM). When added to a concrete mix, metakaolin affects the acceleration of Portland cement hydration when replacing Portland cement by 20 percent by weight.
In ceramics applications, the formula is typically written in terms of oxides, thus the formula for kaolinite is Al2O3·2SiO2·2H2O
Using the cement chemist notation this can be even written as AS2H2, with the oxides respresented as A = Al2O3, S = SiO2, H = H2O.
Kaolinite was also used as filler in Edison Diamond Discs.