sedimentary
Limonite / Goethite (Ironstone)
Hydrated Iron(III) Oxide-Hydroxide FeO(OH)wnH2O
Hardness: 4-5.5; Color: Yellowish-brown to dark brown/black; Luster: Dull to sub-metallic; Cleavage: None; Habbitt: Massive or concretionary
- Hardness
- 4-5
- Color
- Yellowish-brown to dark brown/black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 4-5.5; Color: Yellowish-brown to dark brown/black; Luster: Dull to sub-metallic; Cleavage: None; Habbitt: Massive or concretionary
Formation & geological history
Formed by the oxidation and hydration of iron-bearing minerals or by the precipitation from iron-rich water in bog or swamp environments (Cenozoic to Recent).
Uses & applications
Historically used as a minor iron ore and for brown/yellow mineral pigments (ochre). Primarily of interest to amateur collectors.
Geological facts
Limonite is not a true mineral but a mixture of hydrated iron oxide minerals. It was often called 'bog iron' when found in marshy areas and was the primary source of iron for early civilizations.
Field identification & locations
Identify by its yellowish-brown streak, heavy weight for its size, and absence of magnetism (unless it contains magnetite). Found globally in weathered zones of iron ore deposits.
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