Kaolinite (/ˈkeɪəlɪnaɪt/), a group of natural clay minerals comprising the main ingredients of kaolin (china clay), which are hydrous aluminum silicates. It is part of the Al2Si2O5(OH)4 chemical composition group of industrial minerals. It is easily broken and, especially when wet, can be molded or shaped. Kaolinite is a layered silicate mineral with one tetrahedral sheet of silica (SiO4) bound to one octahedral sheet of alumina (AlO6) octahedra by oxygen atoms. Kaolin/kaolinite-rich rocks are classified as kaolin/ˈkeɪəlɪn/ or Chinese clay.
On its own, kaolinite is a lackluster and uninteresting mineral, but it sometimes forms interesting pseudomorphs, especially after feldspars. Other minerals, including gem crystals in decomposing feldspar pegmatites, are also a common accessory. It is usually white, with often a red impurity due to iron oxide, or blue or brown impurity due to other minerals. Kaolinite has a low limit with regards to recoil swell and a low limit with regards to cation-trade, making it appropriate for some modern applications. In certain parts of the globe, iron oxide is colored pink-orange-red, giving it a distinct rust hue. Lighter concentrations contain colors of white, yellow, or light orange.
Kaolinite, nacrite, and dickite are presented in compact or granular masses and in micalike piles as a minute, often elongated, hexagonal plates. The chemical formula for kaolinite used in mineralogy is Al2Si2O5(OH)4, but the formula is usually written in terms of oxides in ceramic applications, so the formula for kaolinite is Al2O3•2SiO2•2H2O. Kaolinite also has a chemical formula somewhat close to that of Serpentine and is considered a member of the Serpentine group at times.
Crystal structure model of Kaolinite
Anauxite, historically known to have a higher than average silica-alumina ratio as a kaolinite-group mineral, is now known to be kaolinite and free silica (mainly non-crystalline). There are several commercial Kaolinite mines where, for its various industrial uses, this mineral is extracted in large quantities. Kaolinite is used in organic farming as a method of pest control. In medications for diarrhea, nausea, and other stomach disorders, it is an active ingredient. Upon thermal treatment in air at ambient pressure, the Kaolinite group clays undergo a sequence of phase transformations.
Kaolinite is very widespread and has been found worldwide. In Malaysia, Pakistan, Vietnam, Brazil, Bulgaria, Bangladesh, France, the United Kingdom, Iran, Germany, India, Australia, South Korea, the People’s Republic of China, the Czech Republic, Spain, South Africa, Tanzania, and the United States, it is one of the most common minerals; it is mined like kaolin. As a natural resource with its various applications, it is exploited widely across the world. Despite its abundance, due to mediocre aesthetics, Kaolinite is rarely represented in collections.
Production of paper is the main use of the mineral kaolinite (about 50 percent of the time); its use ensures gloss on certain grades of coated paper. In certain drugs, such as stomach soothers, it is used as an ingredient in pharmaceuticals. Kaolinite is also used in some cosmetics, soaps, paint gloss, and toothpaste as an ingredient. By breathing in the powder or through skin or eye contact, people may be exposed to kaolin in the workplace. Kaolinite’s peculiar habits make it readily distinguishable from other minerals. However, without sophisticated detection techniques such as heat absorption or x-ray analysis, other clay minerals may be very close and even difficult to discern.