sedimentary

Bauxite

Bauxite (Mixture of Hydrous Aluminum Oxides)

Hardness: 1-3 on Mohs scale; Color: Reddish-brown, grey, or tan; Luster: Dull to earthy; Crystal structure: Amorphous/massive; Specific gravity: 2.0–2.5; often exhibits a pisolitic (pea-like) structure.

Hardness: 1-3 on Mohs scale
Color: Reddish-brown, grey, or tan
Luster: Dull to earthy

Identified January 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the intense chemical weathering of rocks (like granite or basalt) in hot, tropical, or subtropical climates with high rainfall. It is a residual soil (laterite) where silica has been leached away, leaving enriched aluminum oxides. Most deposits are Cenozoic to Mesozoic in age.

Uses & applications

Primary ore of Aluminum. Used in the production of alumina (Bayer process) and subsequently Aluminum metal. Also used in refractories, abrasives, and chemicals (aluminum sulfate).

Geological facts

Bauxite is not a single mineral but a rock consisting of various minerals including gibbsite, boehmite, and diaspore. The largest producers are Australia, Guinea, and Brazil.

Field identification & locations

Identify in the field by its earthy appearance and lack of distinctive layering; look for small, rounded, pea-sized structures called pisolites. It is soft enough to be scratched by a copper coin and often found in weathered, clay-rich horizons in tropical regions.

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