sedimentary
Sandstone Concretion with Fossil Wood
Ferruginous Sandstone Concretion (SiO2 with Fe2O3 cement)
Hardness: 6-7 (quartz component); Color: Reddish-brown to tan; Luster: Dull/Earthy; Structure: Clastic/Granular with a botryoidal (bumpy) surface; Specific Gravity: ~2.6.
- Hardness
- 6-7 (quartz component)
- Color
- Reddish-brown to tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (quartz component); Color: Reddish-brown to tan; Luster: Dull/Earthy; Structure: Clastic/Granular with a botryoidal (bumpy) surface; Specific Gravity: ~2.6.
Formation & geological history
Formed through the precipitation of mineral cement (often iron oxide) within the spaces between sediment grains, often around a nucleus such as a leaf, bone, or piece of wood. Typically formed in fluvial or marine sedimentary basins during diagenesis.
Uses & applications
Primarily of value to amateur geologists and educators. Fossiliferous specimens are used for studying paleoenvironments.
Geological facts
This specific piece is notable for the inclusion of a petrified or carbonized wood fragment embedded in the center, which served as the 'seed' for the mineral growth. These are often called 'lucky stones' or 'cannonballs' when perfectly spherical.
Field identification & locations
Identify by the distinct color difference between the concretion and the surrounding matrix, and the presence of a central organic nucleus. Commonly found in eroded creek beds or sedimentary outcrops like the Dakota Sandstone formation.
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