sedimentary
Ironstone Concretion / Limonite Crust
Hydrated iron oxide (FeOx·nH2O)
AI-generated identification · may be incorrectHardness of 4-5.5 on the Mohs scale, reddish-brown to dark gray color, submetallic to earthy luster, amorphous crystal structure, and a yellowish-brown streak.
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Physical properties
Hardness of 4-5.5 on the Mohs scale, reddish-brown to dark gray color, submetallic to earthy luster, amorphous crystal structure, and a yellowish-brown streak.
Formation & geological history
Formed through the chemical precipitation of iron oxides in sedimentary environments, often cementing surrounding sand or clay over millions of years.
Uses & applications
Primarily collected as geological specimens or used locally as an informal source of iron ore and pigment.
Geological facts
These hard crusts and concretions often weather out differentially from softer surrounding sandstone because they are more resistant to erosion.
Field identification & locations
Identify in the field by its distinct iron-rust coloration, heavy weight relative to size, and association with sedimentary strata.
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