Bauxite
Bauxite is not a single mineral but a heterogeneous rock composed mainly of aluminum hydroxide minerals, gibbsite, boehmite, and diaspore, mixed with iron oxides, clay, and minor quartz. It forms as a residual deposit left behind after intense chemical weathering strips more soluble elements from aluminum-rich parent rock in tropical and subtropical climates. Bauxite is the world's principal ore of aluminum and typically shows a pisolitic, pea-like texture.
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Bauxite properties at a glance
| Type | Minerals |
|---|---|
| Mohs hardness | 1–3 |
| Luster | Dull, earthy; slight luster on pisoliths |
| Streak | White to yellowish |
| Fracture | Earthy, conchoidal in pisoliths |
| Specific gravity | 2.0–2.55 |
| Transparency | Opaque |
| Common colors | Reddish brown, Tan, Gray, White, Yellow |
| Rarity | common |
Geology & background
Bauxite develops through lateritic weathering, in which heavy rainfall and warm temperatures leach silica and other soluble elements out of aluminosilicate rocks such as granite, basalt, or nepheline syenite, leaving an aluminum- and iron-enriched residue at the surface. This process requires many thousands of years of stable tropical or subtropical climate, which is why the world's major deposits cluster in regions like Australia, Guinea, Jamaica, and Brazil that have experienced prolonged weathering under such conditions.
For rockhounds, bauxite is more interesting geologically than aesthetically; its earthy, pisolitic texture of small rounded pellets is diagnostic, but the rock itself is dull and clay-like rather than crystalline. It is worth collecting as an example of a residual weathering deposit and as the raw material later processed by the Bayer process into alumina and then metallic aluminum. Because composition varies with weathering intensity, individual specimens can range from soft and earthy to hard and pisolitic.
How to identify Bauxite
Bauxite appears as a dull, earthy rock, usually reddish-brown, tan, or gray, often mottled and studded with small rounded pellets called pisoliths a few millimeters across. Luster ranges from dull to earthy, streak is typically pale yellow to reddish-brown from included iron oxide, and hardness is low and variable, generally 1 to 3, since it is a mixture rather than a single mineral. It lacks cleavage and breaks with an irregular, crumbly fracture. Bauxite is sometimes confused with laterite or iron-rich clay, but its characteristic pisolitic texture and aluminum-hydroxide composition set it apart.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Bauxite is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Bauxite worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Bauxite is named after Les Baux-de-Provence in southern France, where the rock was first formally described in 1821.
- Producing one ton of aluminum metal typically requires roughly four tons of bauxite ore.
- Bauxite forms only under intense, prolonged tropical weathering, which is why global deposits concentrate near the equator.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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