sedimentary
Kaolinite (Chalky Clay)
Kaolinite (Al2Si2O5(OH)4)
Hardness: 2.0-2.5 on Mohs scale; Color: White to off-white; Luster: Dull, earthy; Crystal Structure: Triclinic; Cleavage: Perfect; Specific Gravity: 2.6
- Hardness
- 2
- Color
- White to off-white
- Luster
- Dull, earthy
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Physical properties
Hardness: 2.0-2.5 on Mohs scale; Color: White to off-white; Luster: Dull, earthy; Crystal Structure: Triclinic; Cleavage: Perfect; Specific Gravity: 2.6
Formation & geological history
Formed by the chemical weathering of aluminum silicate minerals like feldspar. It is a secondary mineral that develops in moist, hot climates through the hydro-thermal alteration of igneous rocks.
Uses & applications
Primary use in the production of paper (as a coating/filler), ceramics, porcelain, toothpaste, and cosmetics. It is also used in the manufacture of paint and rubber.
Geological facts
The name 'Kaolin' is derived from 'Gaoling', a village in Jiangxi Province, China, where the material was mined for centuries to create fine porcelain.
Field identification & locations
Identify in the field by its soft, earthy texture and white streak. It often sticks to the tongue due to its high absorbent qualities. Common in the Southeastern United States, Brazil, and China.
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