, Size: 1 Kg

Kaolinite is a clay mineral with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral known as china clay or kaolin. Our kaolinite is a calcined kaolin, a dehydroxylated aluminum silicate produced by controlled, high-temperature heating of water-fractionated kaolin. While it is calcined at high temperatures, it is not a metakaolin, which is typically produced by calcining kaolinite at higher temperatures to yield an amorphous, highly reactive material that serves as a pozzolan in cement and concrete applications.

Kaolinite is the standard of the coating industry as an extender pigment in paint systems where high whiteness and good opacifying properties are required. It is used in both solvent and water-based coatings as an extender for titanium dioxide and other prime pigments. Because of its medium-coarse particle size, it provides good sheen control and excellent scrub resistance. It is also used in polymers to provide stiffness, dimensional stability, and good electrical properties. Because the product has been heat treated at a high temperature, it also offers good heat and chemical resistance and a low moisture content.

The name is derived from Gaoling or Kao-Ling ("High Hill") in Jingdezhen, Jiangxi province, China. Kaolinite was first described as a mineral species in 1867 for an occurrence in the Jari River basin of Brazil.

Kaolinite is one of the most common minerals on earth. It is mined as kaolin in Brazil, France, the United Kingdom, Germany, India, Australia, Korea, the People's Republic of China, and the USA.

Kaolinite is a soft, earthy, usually white mineral produced by the chemical weathering of aluminum silicate minerals like feldspar. In many parts of the world, iron oxide colors it pink-orange-red, giving it a distinct rust hue. Lighter concentrations of iron oxide yield white, yellow, or light orange colors. Alternating layers of colored clay are sometimes found at Providence Canyon State Park in Georgia, USA.

Our white kaolin clay is from deposits in Texas, USA, and is heat-treated to remove some of its hydroxyl (OH) composition. Calcined kaolin is produced by heating ultrafine natural kaolinite to high temperatures in a kiln. The calcination process increases whiteness and hardness and alters the size and shape of the kaolin particles.

Kaolin-type clays undergo a series of transformations upon heating in air at atmospheric pressure. Dehydration begins at 550–600° C to produce disordered metakaolin, Al2Si2O7, but continuous hydroxyl loss (-OH) is observed up to 900° C. Due to disagreement concerning the nature of metakaolin, research has led to the consensus that metakaolin is not a simple mixture of amorphous silica (SiO2) and alumina (Al2O3) but rather a complex amorphous structure that retains some longer-range order (but not strictly crystalline) due to stacking of its hexagonal layers.

Between 100–200° C, clay minerals lose most of their adsorbed water. Between 500–800° C, kaolinite becomes calcined by losing water through dehydroxylation. At this temperature range, kaolinite becomes metakaolin, with a two-dimensional order in the crystal structure. To produce a pozzolan, nearly complete dehydroxylation must be reached without overheating. This produces an amorphous, highly pozzolanic state, whereas overheating can cause sintering to form the dead, burnt, nonreactive refractory, called mullite.

Calcined kaolin is used as a functional extender in paint. For example, it has proven to be an excellent extender for titanium dioxide (white) pigment in paint. This is because kaolin clay is chemically inert, has a high covering power, gives desirable flow properties, and reduces the amount of expensive pigments required. Its hardness also improves the physical durability of the paint film and its burnish resistance.

Kaolin clay is also used in grounds for painting and gilding. It can be used in recipes calling for "pipe clay," mixed with starch or flour to make a thick cream, and applied to wood panels or canvas supports for painting. The ground dries quickly, and several very thin layers are applied one after another to form a ground typical of 19th-century paintings.