sedimentary
Sandstone Geode (Ironstone Concretion)
Arenite with Limonite/Hematite matrix (SiO2 with Fe-oxides)
Hardness: 6-7 (Mohs); Color: Reddish-brown, tan, or ochre; Luster: Dull or earthy; Crystal structure: Amorphous or microcrystalline; Cleavage: None; Specific gravity: Approx. 2.5-3.0.
- Hardness
- 6-7 (Mohs)
- Color
- Reddish-brown, tan, or ochre
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Reddish-brown, tan, or ochre; Luster: Dull or earthy; Crystal structure: Amorphous or microcrystalline; Cleavage: None; Specific gravity: Approx. 2.5-3.0.
Formation & geological history
Formed through the precipitation of mineral cement, often iron oxides or carbonates, within the spaces between sediment grains. These often grow around a central nucleus in sedimentary basins. Geological age varies greatly from Paleozoic to Cenozoic eras.
Uses & applications
Used primarily as decorative garden stones, metaphysical or 'shaman' stones (Moqui marbles), and for amateur lapidary use to check for internal crystals.
Geological facts
Many of these spherical stones are actually hollow or contain loose sand/crystals inside. When found in specific areas like Utah, they are famously known as 'Moqui Marbles.' They also mimic the 'blueberries' found by the Mars rover Opportunity.
Field identification & locations
Identify in the field by their spherical or discoid shape and heavy feel relative to other rocks. Common in desert environments and sandstone outcrops. Collectors look for unbroken, perfectly spherical specimens.
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