mineral
Gossan (Iron Hat)
Hydrous Iron Oxides (predominantly Goethite FeO(OH) and Limonite)
Hardness: 5.0-5.5 (variable); Color: Rust-red, yellow, brown; Luster: Dull or earthy; Crystal Structure: Amorphous/Orthorhombic; Cleavage: None; Specific Gravity: 3.3-4.3
- Hardness
- 5
- Color
- Rust-red, yellow, brown
- Luster
- Dull or earthy
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Physical properties
Hardness: 5.0-5.5 (variable); Color: Rust-red, yellow, brown; Luster: Dull or earthy; Crystal Structure: Amorphous/Orthorhombic; Cleavage: None; Specific Gravity: 3.3-4.3
Formation & geological history
Formed by the oxidation and leaching of sulfide mineral deposits (like pyrite or chalcopyrite) at or near the Earth's surface. This process results in the removal of sulfur and metals, leaving behind a residue of iron oxides.
Uses & applications
Historically used as an indicator for underlying ore deposits such as copper, gold, or silver. Small amounts are used as mineral pigments (ochre).
Geological facts
Gossans were famously known as 'iron hats' by early miners because finding one often meant a rich vein of valuable metals lay just beneath the oxidized surface.
Field identification & locations
Identified by its porous (vuggy) texture and distinct rusty-orange to dark brown staining. Found in mining districts globally where sulfide veins outcrop.
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