sedimentary
Moqui Marble (Ironstone Concretion)
Goethite-Hematite Sandstone Concretion
Hardness: 5.0 to 5.5 on Mohs scale; Color: Reddish-brown to dark brown/black exterior; Luster: Dull, earthy to sub-metallic; Structure: Spherical or subspherical mass with a hard iron oxide shell and a softer sandstone core; Specific Gravity: varies (around 3.0-4.0).
- Hardness
- 5
- Color
- Reddish-brown to dark brown/black exterior
- Luster
- Dull, earthy to sub-metallic
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Physical properties
Hardness: 5.0 to 5.5 on Mohs scale; Color: Reddish-brown to dark brown/black exterior; Luster: Dull, earthy to sub-metallic; Structure: Spherical or subspherical mass with a hard iron oxide shell and a softer sandstone core; Specific Gravity: varies (around 3.0-4.0).
Formation & geological history
Formed by the precipitation of iron oxide (hematite and goethite) within permeable sandstone layers, likely during the Jurassic period (Navajo Sandstone), approximately 180-190 million years ago. These concretions grow as minerals crystallize around a nucleus in groundwater.
Uses & applications
Primarily used as metaphysical 'shaman stones,' educational geological specimens, and unique decorative collectibles. Not used in heavy industry due to their small size and specific unique morphology.
Geological facts
Legend holds that the spirits of the Hopi ancestors play games with these 'marbles' at night. They are legally protected within many national park areas in the US, making federal collection illegal in places like Zion or Arches.
Field identification & locations
Identified by their nearly perfect spherical shape and chocolate-brown exterior. They are most famously found in the Navajo Sandstone of Southern Utah. Collectors should look for them weathering out of sandstone cliffs or resting on desert floors.
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