Sandstone Concretion with Fossil Wood

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.

Identified on: 4/13/2026

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