sedimentary
Bauxite
Bauxite (Al2O3·nH2O)
Hardness: 1-3 on Mohs scale; Color: Reddish-brown, white, tan, or yellow; Luster: Dull to earthy; Structure: Pisolitic (rounded, pea-like grains); Specific Gravity: 2.0-2.5.
- Hardness
- 1-3 on Mohs scale
- Color
- Reddish-brown, white, tan, or yellow
- Luster
- Dull to earthy
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Physical properties
Hardness: 1-3 on Mohs scale; Color: Reddish-brown, white, tan, or yellow; Luster: Dull to earthy; Structure: Pisolitic (rounded, pea-like grains); Specific Gravity: 2.0-2.5.
Formation & geological history
Formed as a residual soil in tropical and subtropical regions through the intense chemical weathering (laterization) of silicate rocks like granite or basalt. It is typically found in geological profiles from the Cenozoic era.
Uses & applications
Primary ore of aluminum. Used in the production of alumina (Bayer process), refractories, abrasives, and chemical catalysts.
Geological facts
Bauxite is not technically a mineral but a rock composed mainly of aluminum oxide minerals like gibbsite, boehmite, and diaspore. The rounded 'peas' seen in specimens are called pisolites.
Field identification & locations
Identify in the field by its distinct pisolitic texture (concretionary structures) and earthy smell when damp. Common in Australia, Guinea, Brazil, and Jamaica. Collectors look for high-contrast pisolites.
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