sedimentary
Ironstone Concretion (Moqui Marble)
Ironstone concretion (Fe2O3 with a sandstone core)
Hardness: 5-5.5 (outer shell); Color: Dark brown, black, to reddish-orange; Luster: Dull, earthy, or metallic; Crystal structure: Amorphous/Microcrystalline; Specific gravity: 3.5-4.5; Hard, compacted outer rind with a softer sandy interior.
- Hardness
- 5-5
- Color
- Dark brown, black, to reddish-orange
- Luster
- Dull, earthy, or metallic
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Physical properties
Hardness: 5-5.5 (outer shell); Color: Dark brown, black, to reddish-orange; Luster: Dull, earthy, or metallic; Crystal structure: Amorphous/Microcrystalline; Specific gravity: 3.5-4.5; Hard, compacted outer rind with a softer sandy interior.
Formation & geological history
Formed during the Jurassic period within porous sandstones. Ground water rich in dissolved iron precipitates minerals (limonite/hematite) around a nucleus, hardening into a sphere over millions of years.
Uses & applications
Commonly used as metaphysical 'shaman stones' or 'Moqui marbles,' displayed in geological collections, and studied to understand ancient groundwater chemistry on Earth and Mars.
Geological facts
Identical concretions nicknamed 'Blueberries' were discovered on Mars by the Opportunity rover, suggesting that water was once present on the Red Planet.
Field identification & locations
Identify in the field by its spherical or disc-like shape, heavy weight for its size, and 'halo' of iron oxide. Commonly found in the Navajo Sandstone of Utah and Arizona.
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