mineral

Limonite / Goethite (Iron Ore Mineral nodule)

FeO(OH)·nH2O / FeO(OH)

AI-generated identification · may be incorrect

Hardness: 4.0 - 5.5 on Mohs scale; Color: Dark yellowish-brown, reddish-brown, to dark brownish-black; Luster: Earthy, dull, to sub-metallic; Fracture: Irregular to sub-conchoidal; Specific Gravity: 2.7 - 4.3

Hardness: 4
Color: Dark yellowish-brown, reddish-brown, to dark brownish-black
Luster: Earthy, dull, to sub-metallic

Identified July 26, 2026More mineral →

Explore Limonite / Goethite (Iron Ore Mineral nodule) in the encyclopedia →

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Physical properties

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of primary iron-bearing minerals (such as pyrite, marcasite, or magnetite) in surface sedimentary environments and soil profiles.

Uses & applications

Historically used as an important iron ore and as a source of yellow-brown ochre pigments for paints and cosmetics. Primarily collected as a geological specimen.

Geological facts

Limonite is not a true single mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It often forms pseudomorphs after other minerals like pyrite, retaining the original shape while changing composition.

Field identification & locations

Identified by its distinctive rusty brown to dark yellowish-brown color, heavy weight due to iron content, and yellowish-brown streak on unglazed porcelain. Common in iron-rich sedimentary deposits and oxidized zones worldwide.