sedimentary
Moqui Marble (Iron Concretion)
Hematite-Goethite Concretion
Hardness: 5-5.5 | Color: Dark brown to reddish-black outer shell, tan/yellow interior | Luster: Dull to metallic | Structure: Spherical sand-filled nodules | Specific Gravity: ~3.5-4.5
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 | Color: Dark brown to reddish-black outer shell, tan/yellow interior | Luster: Dull to metallic | Structure: Spherical sand-filled nodules | Specific Gravity: ~3.5-4.5
Formation & geological history
Formed over millions of years by the precipitation of iron-rich minerals in groundwater within porous sandstone, particularly the Navajo Sandstone in Utah during the Jurassic-Cretaceous periods.
Uses & applications
Primarily collected as geological curiosities, used in decorative lapidary arts, and used by some in metaphysical practices.
Geological facts
These are also known as Moqui Marbles, named after the Hopi tribe. Mars Rover Opportunity found similar iron-rich spherules on Mars, nicknamed 'Martian Blueberries'.
Field identification & locations
Identified by their round, marble-like shape and dark, heavy iron rind. They are commonly found in the American Southwest. Collection on Grand Staircase-Escalante and other National Parks is illegal.
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