sedimentary
Gossan (with Limonite/Hematite coating)
Ferruginous Gossan (Fe2O3·nH2O / Fe2O3)
Hardness: 4-5.5 (Mohs); Color: Rusty orange, yellow-brown, dark brown to black; Luster: Dull/Earthy to Sub-metallic; Texture: Porous, vuggy, or massive crust.
- Hardness
- 4-5
- Color
- Rusty orange, yellow-brown, dark brown to black
- Luster
- Dull/Earthy to Sub-metallic
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Physical properties
Hardness: 4-5.5 (Mohs); Color: Rusty orange, yellow-brown, dark brown to black; Luster: Dull/Earthy to Sub-metallic; Texture: Porous, vuggy, or massive crust.
Formation & geological history
Formed by the intense chemical weathering and oxidation of primary sulfide minerals (like pyrite or chalcopyrite) in an ore body, often leaving a concentrated residue of iron oxides.
Uses & applications
Used as a vertical guide or 'iron hat' for geologists to locate underlying metal ore deposits like copper, gold, or silver.
Geological facts
Gossans are historically known as 'iron hats' (einsener hut) by miners because they sit atop unoxidized ore bodies like a cap.
Field identification & locations
Identify by its distinctive rust-like staining on host rock and its lightweight, porous nature compared to the unweathered rock. Found in mining districts worldwide.
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