sedimentary
Ironstone Concretion (Moqui Marble type)
Ironstone Concretion (Fe2O3 with SiO2 core)
Hardness: 5-5.5 (Mohs scale), Color: Dark brown to black outer shell with reddish-yellow interiors, Luster: Dull to sub-metallic, Crystal Structure: Amorphous or microcrystalline, Cleavage: None, Specific Gravity: 3-4
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Dark brown to black outer shell with reddish-yellow interiors, Luster: Dull to sub-metallic, Crystal Structure: Amorphous or microcrystalline, Cleavage: None, Specific Gravity: 3-4
Formation & geological history
Formed by the precipitation of iron oxide minerals around a nucleus (often sand) within sedimentary rock layers, typically occurring in groundwater environments during the Jurassic to Cenozoic eras.
Uses & applications
Primarily used as educational geological specimens, in metaphysical collecting, and occasionally as minor iron ore in historical contexts.
Geological facts
These are often called 'Moqui Marbles' or 'Shaman Stones' in the American Southwest and are famous for their perfectly spherical shapes found in the Navajo Sandstone. They are geologically similar to the 'blueberries' found on Mars by the Opportunity rover.
Field identification & locations
Identify by the heavy weight (high iron content), dark brown rind, and spherical or botryoidal shape. Commonly found in desert environments like Utah, USA, and outcropping from sandstone cliffs.
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