sedimentary
Sandstone Concretion
Moqui Marble / Iron-oxide Concretion (SiO2 with Hematite/Goethite)
Hardness: 6-7 (outer shell); Color: Tan, brown, or earthy red; Luster: Dull to earthy; Crystal structure: Amorphous/Granular; Specific gravity: Approx 2.5-3.0
- Hardness
- 6-7 (outer shell)
- Color
- Tan, brown, or earthy red
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (outer shell); Color: Tan, brown, or earthy red; Luster: Dull to earthy; Crystal structure: Amorphous/Granular; Specific gravity: Approx 2.5-3.0
Formation & geological history
Formed through the precipitation of mineral cement (typically iron oxide or calcite) within the spaces between sediment grains, often around a nucleus like a leaf or shell. Often dating to the Jurassic or Cretaceous periods.
Uses & applications
Primary uses are as educational specimens, collector items, and in metaphysical practices (shaman stones). Larger deposits are studied for geological mapping.
Geological facts
Geologists have found remarkably similar 'blueberries' on Mars, which helped prove the presence of water in Mars' ancient history. Smaller versions are often called 'Moqui Marbles'.
Field identification & locations
Identify by its spherical or disc-like shape that stands out from the surrounding rock layers. Often found weathering out of sandstone cliffs in arid regions like the American Southwest.
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