sedimentary
Limonite (Iron Ore)
Hydrous ferric oxides (FeO(OH)·nH2O)
Hardness: 4-5.5 | Color: Yellowish-brown to dark brown | Luster: Dull, earthy | Crystal Structure: Amorphous | Cleavage: None | Specific Gravity: 2.7-4.3
- Hardness
- 4-5
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Physical properties
Hardness: 4-5.5 | Color: Yellowish-brown to dark brown | Luster: Dull, earthy | Crystal Structure: Amorphous | Cleavage: None | Specific Gravity: 2.7-4.3
Formation & geological history
Formed through the oxidation and hydration of iron-rich mineral deposits (like pyrite or magnetite) in weathered environments or boggy areas.
Uses & applications
Historically used as a major iron ore and as a pigment for yellow ocher; currently used in construction materials and occasionally as specimen pieces.
Geological facts
Limonite is not a single mineral but a mixture of related hydrated iron oxide minerals, most commonly goethite. It has been used as a pigment (ocher) by humans for over 30,000 years in cave paintings.
Field identification & locations
Identify by its brownish-yellow streak on porcelain and its earthy, rusty appearance. Commonly found in gossans (weathered zones above ore bodies) and sedimentary iron beds.
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