Kaolinite (redirected from Kaolin clay)

kaolinite (kā`əlĭnīt), clay mineral crystallizing in the monoclinic system and forming the chief constituent of china clay and kaolin. It is a hydrous aluminum silicate commonly formed by the weathering and decomposition of rocks containing aluminum silicate compounds; feldspar is a chief source. Kaolinite has the same chemical composition as dickite and nacrite (both of which are also clay or kaolin minerals) but differs from them in origin, in optical properties, in reaction to heat, and in certain other physical properties. Kaolinite is the basic raw material for ceramics, and large quantities are also used in the manufacture of coated paper.

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kaolinite

Group of common clay minerals that are hydrous aluminum silicates and constitute the principal ingredients of kaolin (china clay). The group includes kaolinite, dickite, nacrite, halloysite, and allophane. They are natural alteration products of feldspars, feldspathoids, and other silicates.

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kaolinite [′kā·ə·lə‚nīt]

(mineralogy)

Al₂Si₂O₅(OH)₄A common hydrous aluminum silicate mineral found in sediments, soils, hydrothermal deposits, and sedimentary rocks. It is a member of the kaolin group of minerals, which include dickite, halloysite, nacrite, ordered kaolinite, and disordered kaolinite.

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kaolinite

One of the clay materials consisting of a hydrous aluminum silicate.

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Kaolinite 

a clay mineral from the group of hydrous aluminum silicates. Its chemical composition is Al₄[Si₄O₁₀] (OH)₈, and it contains 39. 5 percent Al₂O₃, 46.5 percent SiO₂, and 14 percent H₂O. Kaolinite forms earthen masses, in which, with high magnification under an electron microscope, small hexagonal crystals can be detected. It crystallizes in the monoclinic system. The mineral’s crystal structure is based on infinite sheets of Si—0₄ tetrahedrons, which have three common oxygens and are linked in pairs through the free apexes of the crystal lattice by the aluminum and hydroxyl. These sheets are interconnected by weak bonds and this determines the perfect cleavage of kaolinite as well as the possibility of the differing positioning of one layer on the other. This, in turn, leads to a certain change in the symmetry of the entire crystal structure. Kaolinite has a hardness of 1 on the mineralogical scale and a density of 2, 540–2, 600 kg/m³. It is greasy to the touch. In heating to 500°-600° C, it loses water, and at 1,000°-1, 200° C, it decomposes, liberating heat and forming initially sillimanite and then mullite. This reaction constitutes the basis of ceramic production.

A component of many clays, kaolinite is formed during weathering and hydrothermal alteration of feldspathic rock.

V. P. PETROV