sedimentary
Ironstone Concretion
Ferruginous Concretion (Fe2O3·nH2O)
Hardness: 5-5.5 (Mohs scale), Color: Dark brown to reddish-brown, Luster: Dull or earthy, Structure: Amorphous/microcrystalline, Cleavage: None, Specific Gravity: 3.5-4.5.
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Dark brown to reddish-brown, Luster: Dull or earthy, Structure: Amorphous/microcrystalline, Cleavage: None, Specific Gravity: 3.5-4.5.
Formation & geological history
Formed by the precipitation of mineral cement in the spaces between particles in sedimentary rock, usually around a nucleus such as a fossil or shell. These are typically found in sandstone or shale beds and can range from modern times back millions of years.
Uses & applications
Primarily of interest to collectors; historically used as a low-grade iron ore. Sometimes used in decorative rock gardens.
Geological facts
These are often mistaken for meteorites due to their dark color and heavy weight, but they lack a fusion crust. They are colloquially known as 'Moqui Marbles' in specific regions like Utah.
Field identification & locations
Identify by its unusually heavy weight for its size, rusty exterior, and lack of crystal facets. Commonly found in eroded sedimentary landscapes or riverbeds.
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