sedimentary
Limonite Concretion
Hydrated Iron Oxide / FeO(OH)·nH2O
Hardness: 4 to 5.5 on the Mohs scale, Color: Yellowish-brown, reddish-brown, or dark brown, Luster: Submetallic to earthy, Crystal Structure: Amorphous or microcrystalline, Cleavage: None, Specific Gravity: 2.7 to 4.3
- Hardness
- 4 to 5
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Physical properties
Hardness: 4 to 5.5 on the Mohs scale, Color: Yellowish-brown, reddish-brown, or dark brown, Luster: Submetallic to earthy, Crystal Structure: Amorphous or microcrystalline, Cleavage: None, Specific Gravity: 2.7 to 4.3
Formation & geological history
Formed through the oxidation and weathering of iron-bearing sulfide minerals or iron-rich rocks, often precipitating out of iron-bearing groundwater in sedimentary environments.
Uses & applications
Used primarily as an iron ore historically, as a pigment (ochre), and collected as a geological curiosity due to unusual shapes.
Geological facts
Limonite concretions can form fascinating, hollow, or sand-filled shapes often colloquially referred to as 'fairy crosses,' 'shaman stones,' or 'boji stones,' which are popular among new-age collectors.
Field identification & locations
Easily identified by its characteristic yellowish-brown to reddish-brown streak and earthy texture. Commonly found in weathered ironstone formations and residual clay deposits worldwide.
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