What is Kaolinite?
Kaolinite is a soft, fine-grained clay mineral whose layered structure underpins porcelain, paper, pigments and the interpretation of weathered rocks.
Mineralogy and crystal structure
Reference formula: Al2Si2O5(OH)4. Kaolinite has a 1:1 layered phyllosilicate structure made of silica tetrahedral and alumina octahedral sheets. Its fine grain, water interaction and polymorphism require a different approach from identifying a large transparent crystal. Kaolinite is classified with silicates and has a triclinic crystal system. Typical hardness is 2–2.5 on the Mohs scale and specific gravity is approximately 2.6–2.7.
Colour, lustre and habit
Typical colours include white, cream, pale yellow, pink, grey. The usual platey, massive, earthy habit and pearly, dull, earthy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Kaolinite forms in or is associated with intense chemical weathering of feldspar-rich rocks, hydrothermal alteration and sedimentary clay deposits. Important documented localities include China, Brazil, the United States, the United Kingdom, France and Germany.
The quiet mineral behind beautiful surfaces
Kaolinite is a compelling reference material because it connects a modest white clay with high-value ceramics, paper and pigment production. A labelled natural sample makes an elegant addition to a collection focused on materials, industry and Earth-surface processes.
Collecting and care
Avoid breathing dust and keep delicate clay specimens dry and protected from abrasion; do not use a hardness test on powdery material.
