sedimentary
Gossan (with Limonite and Hematite)
Gossanous iron-oxide rock (Fe2O3 · nH2O)
Hardness: 4.0-5.5 (variable); Color: Ochre, rusty brown, dark reddish-purple; Luster: Dull to sub-metallic; Structure: Porous, cellular, or massive; Cleavage: None; Specific Gravity: 2.7-4.3.
- Hardness
- 4
- Color
- Ochre, rusty brown, dark reddish-purple
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 4.0-5.5 (variable); Color: Ochre, rusty brown, dark reddish-purple; Luster: Dull to sub-metallic; Structure: Porous, cellular, or massive; Cleavage: None; Specific Gravity: 2.7-4.3.
Formation & geological history
Formed by the intense oxidation and weathering of sulfide mineral deposits (like pyrite or chalcopyrite) in an oxygen-rich environment above the water table.
Uses & applications
Used historically as an indicator for underlying ore deposits (gold, silver, copper). Sometimes used as a source for iron pigments (ochre).
Geological facts
Miners call the reddish-brown cap 'the iron hat.' It acts as a geological signpost, often leading to rich metal deposits deeper underground.
Field identification & locations
Identify by its 'rusty' appearance and porous texture. Commonly found in mining districts and arid regions. Collectors should look for boxwork textures which indicate former crystals.
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