sedimentary

Limonite (Iron Ore)

Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4-5.5; Color: Yellowish-brown, ochre, rusty orange; Luster: Dull or earthy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 2.7-4.3

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

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown, ochre, rusty orange; Luster: Dull or earthy; Crystal structure: Amorphous; Cleavage: None; Specific gravity: 2.7-4.3

Formation & geological history

Formed by the oxidation (weathering) of iron-rich sulfide minerals like pyrite or as a chemical precipitate in shallow seas and bogs. Often found in gosson zones or bog iron deposits.

Uses & applications

Historically used as an important iron ore; currently used as a yellow-brown pigment (ochre) in paints and dyes, and occasionally as a low-grade building material.

Geological facts

Limonite was one of the earliest pigments used by humans, found in Neolithic cave paintings. It often forms pseudomorphs after other minerals like pyrite.

Field identification & locations

Identify by its distinctive yellow-brown streak and earthy appearance. It is found worldwide in weathered volcanic rocks and sedimentary beds. Collectors look for cubic pseudomorphs.