mineral
Limonite / Ironstone
Hydrated ferric oxide (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; Mohs: 4-5.5; Streak: Yellow-brown.
- 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; Mohs: 4-5.5; Streak: Yellow-brown.
Formation & geological history
Formed by the oxidation and hydration of iron-rich sulfide minerals or as a chemical precipitate in shallow marine or swampy environments (bog iron).
Uses & applications
Historically used as a common ore of iron; used as a pigment (brown ochre) in paints; industrial filler.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, primarily goethite. It has been used as a pigment by humans for over 30,000 years in cave paintings.
Field identification & locations
Identify in the field by its characteristic yellowish-brown streak on a ceramic plate and its earthy, rusted appearance. Often found in weathered zones of ore deposits.
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