Kaolinite - Encyclopedia

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal system : Triclinic
    Chemistry : Al2Si2O5(OH)4
    Rarity : Rare

Kaolinite is the main mineral of the group of the same name, which also includes dickite and nacrite, its two polymorphs. A very common clay mineral, kaolinite is a low-temperature hydrothermal alteration product of potassium feldspars and other aluminum silicates. Kaolinite is found in altered leucogranites, and generally in altered grainy rocks rich in potassium feldspars (particularly orthogneiss). Its name derives from its locality of discovery : the hill of Kao-Ling, near Jaucha Fa (China). Kaolinite rarely forms crystals visible to the naked eye ; it usually appears in compact, friable or powdery, creamy clay masses, made up of microscopic hexagonal lamellae. Bright white when pure, kaolinite is sometimes tinged with brownish, greenish or yellowish. It is the essential, even exclusive, constituent of kaolin, a widely used white clay. It finds its most important use in stationery where it serves as a mass filler and coating filler thanks to its good ink retention, an area where it faces strong competition from calcite and talc. The ceramic industry also offers leading roles with the manufacture of earthenware and porcelain. Kaolinite also has uses in the rubber industry, in the chemical industry (ion exchange material, saponifiers, degreasers, absorbents, fillers for paints, catalysts) and in the food industry (filler in foods , notably chocolate, non-sticky dispersant of agricultural granules, etc...). Kaolinite is also found as a filler in cosmetics and polyester fibers, as an insulator, as a filler in pencil leads, or as a coagulant in water purification.

Main photo : Kaolinite from Les Molérats, Saône-et-Loire, France © Pascal Ollic

Kaolinite in the World

Present almost everywhere, kaolinite forms significant deposits in Kauling (China), Ukraine, Australia and the United States. The sites having provided visible crystals are very rare: Keokuk (Iowa), Vergenoeg (South Africa).

Kaolinite in France

In France, large deposits of kaolinite are exploited in Brittany : Ploëmeur (Morbihan) and Berrien (Finistère) as well as in Auvergne at Echassières (Allier).


No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.

Hardness : 2 to 2.5
Density : 2.68
Fracture : Irregular to micaceous
Streak : White

TP : Opaque to translucent
RI : 1.553 to 1.570
Birefringence : 0.007
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : Insoluble

Magnetism : NoneRadioactivity : None


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