sedimentary

Limonite-stained Gossan/Ironstone

Goethite and Hematite (Fe2O3 • nH2O)

AI-generated identification · may be incorrect

Hardness: 4-5.5 (variable); Color: Dark brown to metallic gray with yellowish-orange oxidation; Luster: Sub-metallic to dull; Structure: Masses or crusts; Cleavage: None

Hardness: 4-5
Color: Dark brown to metallic gray with yellowish-orange oxidation
Luster: Sub-metallic to dull

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5 (variable); Color: Dark brown to metallic gray with yellowish-orange oxidation; Luster: Sub-metallic to dull; Structure: Masses or crusts; Cleavage: None

Formation & geological history

Formed through the intensive chemical weathering and oxidation of iron-rich sulfide minerals or other iron-bearing rocks, often indicating a subsurface ore deposit.

Uses & applications

Historically used as a low-grade iron ore; currently used as a geological indicator for prospecting metal deposits and as a source of pigments (ochre).

Geological facts

Gossans are known as 'iron hats' to miners because they sit over the top of unoxidized ore bodies and were used since antiquity to find copper, gold, and silver.

Field identification & locations

Identifiable by its heavy weight relative to surrounding rocks and its distinct rusty-yellow or orange-brown staining. Found in mining districts and areas with high metal sulfide mineralization.