mineral
Limonite
Limonite (Hydrated iron oxide mixture, FeO(OH)·nH2O)
Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull/Earthy; Crystal structure: Amorphous; 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; Cleavage: None; Specific gravity: 2.7-4.3
Formation & geological history
Formed as a secondary material through the oxidation or chemical weathering of primary iron-bearing minerals like pyrite or magnetite. Often found in Bog Iron deposits or as gossans.
Uses & applications
Historically used as a minor iron ore; primarily used today as an earth pigment (yellow ochre) in paints, and for soil amendment.
Geological facts
Limonite is not a 'true' mineral but a field term for a mixture of hydrated iron oxide minerals, mostly goethite. It was the source of yellow pigments for prehistoric cave paintings.
Field identification & locations
Identify by its characteristic yellowish-brown streak on a porcelain plate and lack of magnetism compared to magnetite. Found in wetlands and weathered iron outcrops.
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