sedimentary
Kaolin Clay in Saprolite Profile
Kaolinite (Al2Si2O5(OH)4) within Weathered Pegmatite/Granite
Hardness: 2-2.5 (Mohs); Color: White, cream, or iron-stained reddish-brown; Luster: Dull, earthy; Crystal structure: Triclinic (microscopic plates); Cleavage: Perfect; Specific gravity: 2.6
- Hardness
- 2-2
- Color
- White, cream, or iron-stained reddish-brown
- Luster
- Dull, earthy
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Physical properties
Hardness: 2-2.5 (Mohs); Color: White, cream, or iron-stained reddish-brown; Luster: Dull, earthy; Crystal structure: Triclinic (microscopic plates); Cleavage: Perfect; Specific gravity: 2.6
Formation & geological history
Formed through the hydrothermal alteration or intense chemical weathering (kaolinization) of feldspar-rich rocks like granite and pegmatite. This outcrop represents a saprolite profile, typically found in tropical environments.
Uses & applications
Used extensively in the paper industry for coating, ceramics, porcelain, toothpaste, cosmetics, and as a filler in rubber and plastics.
Geological facts
Kaolin is also known as China Clay. It is essential for making fine porcelain (fine china). Massive deposits like this often indicate deep tropical weathering over millions of years.
Field identification & locations
Identify in the field by its soft, chalky feel, white to light gray color when pure, and the fact that it stays on your hands like flour when dry and becomes plastic/sticky when wet. Common in West Africa, SE USA, and Brazil.
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