kaolinite (dickite, nacrite, China clay, kaolin) A very important group of clay minerals belonging to the 1:1 group of phyllosilicates (sheet silicates), and with the general formula Al₄[Si₄O₁₀](OH)₈, kaolinite represents the final product from the chemical weathering of feldspars to give clays; sp. gr. 2.6–2.7; hardness 2.0–2.5; monoclinic; white, greyish, or stained a variety of colours; dull earthy lustre; on a microscopic scale crystals are hexagonal plates, but it is usually massive; cleavage phyllosilicates; occurs as a secondary mineral produced by the alteration of aluminosilicates, especially alkali feldspars; is widely distributed in igneous rocks, gneisses, and pegmatites, and in sedimentary rocks due to the action of acidic solutions on a wide variety of rocks by processes of weathering and low-temperature hydrothermal reactions. It is distinguished by its plastic feel, but normally it has to be identified by optical and physical tests. It is extensively used when pure as a cheap, general-purpose filler and coating material for paper, in ceramics, and also in chemicals and paints. It is distinctive in soils for its physical stability during wetting and drying and for its small cation-exchange capacity. Kaolinite dominates the clay minerals present in certain acid and very old soils, but not in Oxisols, some Latosols, or soils formed in arid climates. The name is derived from the Chinese kau-ling (‘high ridge’), referring to the hill from which the first samples were taken.

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.

kaolinite Sheet silicate mineral of the kaolinite group, hydrous aluminium silicate [Al₂Si₂O₅(OH)₄]. It is a product of the weathering of feldspar and has triclinic system tabular crystals. It is white with a dull lustre. Hardness 2–2.5; r.d. 2.6.

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