Bauxite
Hydrated aluminum oxides (mixture of gibbsite Al(OH)3, boehmite and diaspore AlO(OH))
An earthy aluminum-rich residual rock and the world's principal ore of aluminum, often showing distinctive pea-like pisolites.
- Mohs hardness
- 1-3
- Color
- Pinkish, reddish-brown, tan to white or buff
- Type
- sedimentary
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Overview
Bauxite is not a single mineral but a rock made up of a mixture of hydrated aluminum oxide minerals, chiefly gibbsite along with boehmite and diaspore, mixed with iron oxides, clay and silica. It is the primary ore from which nearly all of the world's aluminum is extracted.
Bauxite typically has an earthy, claylike to pisolitic texture, frequently containing small rounded concretions (pisolites or ooliths) that give it a distinctive pea-gravel appearance. Colors range from white and cream through tan to deep reddish-brown depending on iron content.
It is a soft, often friable rock that forms as a residual deposit through intense chemical weathering in warm, wet climates.
Formation & geology
Bauxite forms by intense, prolonged chemical weathering (lateritization) of aluminum-rich parent rocks under tropical and subtropical climates with heavy rainfall and good drainage. As silica and other soluble elements are leached away over long periods, aluminum and iron oxides become concentrated in the residual soil.
Most commercial deposits are residual blankets developed over rocks such as nepheline syenite, basalt, or clay-rich sediments, and karst bauxites form over weathered limestone. Major deposits occur in Australia, Guinea, Brazil, Jamaica, India and China, generally in regions that were tropical at the time of formation.
How to identify it
Look for an earthy, dull to porous rock that is soft (easily scratched) and often light in weight. The most diagnostic feature is pisolitic texture: small spherical concretions like peas or birdshot set in a finer matrix.
Colors run from white and tan to brick-red and brown, often mottled. The streak is pale and it leaves a chalky feel. Bauxite can resemble laterite, claystone or ironstone; the presence of pisolites, its softness, and clay-like odor when breathed on help distinguish it. Unlike pure clay it is gritty and granular, and unlike ironstone it is generally lighter and softer.
Uses & significance
Bauxite is overwhelmingly important as the ore of aluminum: it is refined into alumina (aluminum oxide) by the Bayer process, which is then smelted into metallic aluminum. This makes it foundational to aerospace, transportation, packaging and construction industries.
Non-metallurgical bauxite is used to manufacture abrasives, refractory materials, cement, and proppants for oil and gas drilling. It also serves as a source of gallium recovered as a byproduct. It has no gemstone or significant metaphysical use.
Frequently asked questions
Is bauxite a mineral or a rock?
It is a rock, an aggregate of several hydrated aluminum oxide minerals (gibbsite, boehmite, diaspore) mixed with iron oxides and clay, not a single mineral species.
Why is bauxite important?
It is the world's main source of aluminum; almost all aluminum metal is refined from bauxite via alumina.
What gives bauxite its red color?
Iron oxide impurities. Bauxite low in iron is white or cream, while iron-rich bauxite is reddish-brown.
Where is bauxite found?
In tropical and former-tropical regions such as Australia, Guinea, Brazil, Jamaica, India and China, where deep weathering concentrated aluminum.
Bauxite guides
In-depth guides for identifying, valuing, and understanding Bauxite.
Bauxite identified by the community
Real specimens identified with Rock Identifier.
