mineral/sedimentary
Limonite (Ironstone Concretion)
Limonite (FeO(OH)·nH2O)
Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7 to 4.3.
- Hardness
- 4 to 5
- Color
- Yellowish-brown to dark brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7 to 4.3.
Formation & geological history
Formed through the oxidation of iron-rich mineral deposits in sedimentary environments. Often found as nodules or concretions where iron precipitating from groundwater binds sediment together.
Uses & applications
Historically used as an iron ore and a source of yellow pigment (ochre). Currently utilized primarily in paint production and as mineral specimens for collectors.
Geological facts
Limonite is not a single mineral but a mixture of hydrated iron oxide minerals. It was a primary source of iron for early civilizations and is the material that gives many desert sands and soils their reddish-yellow color.
Field identification & locations
Identify in the field by its characteristic 'rust-colored' streak and earthy appearance. Look for it in iron-rich sedimentary bands or as nodules in clay-rich soils. It is often found near swampy areas or gossans.
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