sedimentary
Moqui Marble (Iron Concretion)
Hematite/Goethite Concretion (Fe2O3 / FeO(OH))
Hardness: 5-6 (outer shell); Color: dark brown to sandy tan; Luster: dull, earthy, or sub-metallic; Crystal structure: massive or botryoidal shell; Cleavage: none; SG: 3.4-5.0
- Hardness
- 5-6 (outer shell)
- Color
- dark brown to sandy tan
- Luster
- dull, earthy, or sub-metallic
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Physical properties
Hardness: 5-6 (outer shell); Color: dark brown to sandy tan; Luster: dull, earthy, or sub-metallic; Crystal structure: massive or botryoidal shell; Cleavage: none; SG: 3.4-5.0
Formation & geological history
Formed by the precipitation of iron-rich groundwater minerals around a nucleus (often sand) within sandstone layers, primarily during the Jurassic period.
Uses & applications
Mainly used as geological specimens, metaphysical stones ('shaman stones'), and for educational purposes in earth science.
Geological facts
They are often called 'Moqui Marbles' after the Hopi tribe; similar structures known as 'blueberries' were discovered by the Opportunity rover on Mars.
Field identification & locations
Identify by their spherical shape and dark iron crust over a sandstone core; found commonly in the Navajo Sandstone of Utah and Arizona.
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