Kaolinite is a common 1:1 dioctahedral phyllosilicate (clay) mineral found in soils across the world, particularly in highly-weathered environments, as well as scattered monomineralic deposits that are mined for industry. Being a 1:1 mineral, each kaolinite layer has one silica tetrahedral sheet and one alumina octahedral sheet. Individual layers are held together in a crystal by O – H – O bonds between the octahedral sheet of one layer and the tetrahedral sheet of the adjacent layer.
The crystallography of kaolinite played an important role in Linus Pauling’s formulation of the nature of the chemical bond, although for 15 years kaolinite was thought to be monoclinic (crystallographic axes all equal to 90°) instead of triclinic. Crystallographic axes: alpha, 91.8°; beta 104.7°; gamma, 90°).
The crystal structure displayed to the left, including all H atoms, is based on low-temperature (1.5° K) neutron powder diffraction data (Bish, 1993) instead of the more common x-ray diffraction data that has been used since the time of Linus Pauling’s original determination of the crystal structure of kaolinite in 1930.
Highlighting FeaturesPlane of Si atoms Single silica tetrahedron Silica tetrahedral sheet Plane of Al atoms Single alumina octahedron Alumina octahedral sheet Single unit cell Show all atoms
Kaolinite normally is present as stacks of kaolinite layers, usually with an overall hexagonal appearance. View a larger, multi-layer crystal of kaolinite.
Kaolinite is widely distributed in nature. Pure deposits are mined for paper coatings and porcelain, both bathroom fixtures and fine China cups. Most soils of the world contain kaolinite in the clay size fraction (<2 µm). In highly weathered soils, such as those of Southeastern U.S. and tropical regions of Africa, Asia, and S. America, kaolinite is usually the dominant clay mineral because of its relative resistance to chemical weathering.
Bish, D.L. 1993. Rietveld refinement of the kaolinite structure at 1.5 K. Clays & Clay Minerals. 41:738-744.
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