sedimentary
Bauxite (Iron-stained Chert / Ironstone Aggregate)
Hydrous aluminum oxide mixture (mainly Gibbsite Al(OH)3, Boehmite γ-AlO(OH), and Goethite α-Fe3+O(OH))
Hardness: 1-3 (soft, earthy matrix, though included chert/quartz can be 7). Color: Reddish-brown, orange-brown, tan, with earthy to dull luster. Structure: Earthy, pisolitic, or fine-grained massive texture. Specific Gravity: 2.0-2.5.
- Color
- Reddish-brown, orange-brown, tan, with earthy to dull luster
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Physical properties
Hardness: 1-3 (soft, earthy matrix, though included chert/quartz can be 7). Color: Reddish-brown, orange-brown, tan, with earthy to dull luster. Structure: Earthy, pisolitic, or fine-grained massive texture. Specific Gravity: 2.0-2.5.
Formation & geological history
Formed in tropical to subtropical climates by intense chemical weathering (leaching) of aluminum-rich rocks over millions of years, often concentrated with iron oxides (goethite/hematite) giving it a rich reddish-tan rusty coating.
Uses & applications
Bauxite is the primary global ore used for manufacturing aluminum metal. Iron-rich variants and ironstones are also used as construction aggregates or decorative landscape stones.
Geological facts
Bauxite isn't a single mineral, but a rock composed mostly of aluminum oxide minerals mixed with iron oxides, silica, and clay. Australia, Guinea, and China hold the world's largest deposits.
Field identification & locations
Look for a rust-colored, earthy, unpolished surface that leaves a yellowish-red streak. Common in weathered tropical soil zones, stream beds, and sedimentary gravel beds. Soft enough to scratch easily compared to hard silicates unless silicified.
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