sedimentary
Limonite (Iron Ore)
Hydrated iron(III) oxide-hydroxide (FeO(OH)·nH2O)
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
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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.
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