mineral
Limonite (Iron Ore)
Limonite (Hydrated iron(III) oxide-hydroxide, FeO(OH)·nH2O)
AI-generated identification · may be incorrectHardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (no visible crystals); Cleavage: None; Specific Gravity: 2.7-4.3
- Hardness
- 4
- Color
- Yellowish-brown to dark brown
- Luster
- Dull, earthy
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Physical properties
Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (no visible crystals); Cleavage: None; Specific Gravity: 2.7-4.3
Formation & geological history
Formed as a secondary material through the oxidation or weathering of other iron-bearing minerals (like pyrite or magnetite). Often found in bog deposits or weathered outcrops.
Uses & applications
Historically used as an iron ore; currently used as a pigment (ochre) for paints and dyes. Large deposits are mined for steel production.
Geological facts
Limonite is not a true mineral but a mixture of similar hydrated iron oxides (mostly Goethite). It was used by prehistoric humans as a cave painting pigment.
Field identification & locations
Identify by its 'rust' color and yellowish-brown streak on a porcelain plate. Common in boggy areas or as 'iron hats' (gossans) on top of ore deposits. It is heavy for its size compared to organic matter.
