Limonite and Goethite on Gossan

Physical Properties

Hardness: 4-5.5 (Mohs), Color: Yellowish-brown to dark brown, Luster: Dull to submetallic, Crystal structure: Amorphous/Orthorhombic microcrystalline, Specific Gravity: 2.7-4.3

Formation & Geological History

Formed as a secondary mineral through the oxidation and weathering of iron-rich sulfide minerals (like pyrite) in the 'gossan' or iron hat of an ore deposit.

Uses & Applications

Primarily used as a minor ore of iron; historically used as a natural pigment (ochre). Collected by geologists as an indicator of underlying metal deposits.

Geological Facts

Limonite is not a true mineral species but a field term for unidentified massive hydroxides of iron. It was once a primary source of iron for early humans and is the 'yellow' in yellow ochre.

Field Identification & Locations

Identify in the field by its distinct mustard-yellow to brown streak and earthy appearance. Often found in weathered outcrops of mining districts. Caution: specimens from mining areas can contain toxic trace elements.

Identified on: 4/30/2026

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