mineral

Gossan (Limonite/Goethite)

Hydrated iron oxides (primarily FeO(OH)·nH2O)

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to rusty orange; Luster: Dull, earthy; Crystal structure: Amorphous or microcrystalline; Cleavage: None; Specific gravity: 2.7-4.3

Hardness: 4-5
Color: Yellowish-brown to rusty orange
Luster: Dull, earthy

Identified April 9, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to rusty orange; Luster: Dull, earthy; Crystal structure: Amorphous or microcrystalline; Cleavage: None; Specific gravity: 2.7-4.3

Formation & geological history

Formed through the intense oxidation and weathering of primary sulfide mineral deposits (like pyrite or chalcopyrite) near the Earth's surface, often creating a 'rusty cap' over deeper ore bodies.

Uses & applications

Historically used as an iron ore; currently used as a geological marker/indicator for explorers searching for gold, copper, and lead deposits beneath the surface.

Geological facts

The word 'Gossan' comes from Cornish mining terminology. These formations were vital for early miners as they acted as giant 'signposts' for valuable metals hidden underground.

Field identification & locations

Identify by its porous, 'cinder-like' texture and distinct rusty-orange staining. Typically found in arid or temperate climates where sulfide veins are exposed to oxygen and water.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral