sedimentary
Moqui Marble (Ironstone Concretion)
Goethite/Hematite Concretion (Fe2O3 / FeO(OH))
Hardness: 5-6 (outer shell); Color: Rusty brown, dark chocolate brown, to black; Luster: Dull, earthy; Structure: Spherical or disc-like concretion; Specific Gravity: 3.4-5.0
- Hardness
- 5-6 (outer shell)
- Color
- Rusty brown, dark chocolate brown, to black
- Luster
- Dull, earthy
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Physical properties
Hardness: 5-6 (outer shell); Color: Rusty brown, dark chocolate brown, to black; Luster: Dull, earthy; Structure: Spherical or disc-like concretion; Specific Gravity: 3.4-5.0
Formation & geological history
Formed by the precipitation of iron oxide minerals around a nucleus (often sand) within groundwater-soaked sedimentary layers, primarily the Navajo Sandstone. They are roughly 25 to 190 million years old.
Uses & applications
Geological collecting, metaphysical use (energy stones), and planetary research (analogues for 'blueberries' on Mars).
Geological facts
The name 'Moqui' comes from the Hopi tribe. NASA scientists study these because similar hematite spherules were found on Mars by the Opportunity rover, suggesting a watery past for the red planet.
Field identification & locations
Identified by their nearly perfect spherical or button shape and heavy iron-rich weight. Commonly found in the American Southwest (Utah/Arizona), they often weather out of sandstone cliffs.
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