sedimentary
Limonite Concretion
Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)wnH2O)
Hardness: 4-5.5 (Mohs scale), Color: Yellowish-brown to dark brown, Luster: Dull or earthy, Crystal Structure: Amorphous or nanocrystalline, Cleavage: None, Specific Gravity: 2.7-4.3
- Hardness
- 4-5
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Physical properties
Hardness: 4-5.5 (Mohs scale), Color: Yellowish-brown to dark brown, Luster: Dull or earthy, Crystal Structure: Amorphous or nanocrystalline, Cleavage: None, Specific Gravity: 2.7-4.3
Formation & geological history
Formed by the oxidation of iron-bearing minerals or by precipitation from iron-rich groundwater in sedimentary environments. Common in swampy areas or bog-iron deposits.
Uses & applications
Historically used as a low-grade iron ore and as a pigment for ochre paints. Today, primarily collected by hobbyists or used in educational displays.
Geological facts
Limonite is not a true mineral but a mixture of similar hydrated iron oxide minerals, mainly goethite. It has been used as a pigment (Yellow Ochre) since prehistoric times for cave paintings.
Field identification & locations
Identify by its brownish-yellow streak on ceramic surfaces and its lack of magnetism compared to magnetite. Found in sedimentary basins, marshes, and weathered ore outcrops worldwide.
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