sedimentary

Sandstone Concretion

Clastic Sedimentary Rock (primarily SiO2 with mineral cement)

AI-generated identification · may be incorrect

Hardness: 6-7 (on Mohs scale for quartz grains); Color: Tan, beige, or brown with concentric banding; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.3–2.6.

Hardness: 6-7 (on Mohs scale for quartz grains)
Color: Tan, beige, or brown with concentric banding
Luster: Dull/Earthy

Identified March 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of mineral cement within the spaces between sediment grains (usually sand). This often occurs around a nucleus, such as a leaf, shell, or bone, during diagenesis in sedimentary basins. They can range from thousands to millions of years old.

Uses & applications

Primarily used as decorative display pieces, garden stones, or educational geological specimens. In larger scales, sandstone is used in construction, but concretions are usually kept as curiosities.

Geological facts

Concretions are often mistaken for fossilized eggs or man-made artifacts because of their remarkably round or symmetrical shapes. Some famous examples include the Moeraki Boulders in New Zealand, which are massive versions of this phenomenon.

Field identification & locations

Identify in the field by looking for unusually round or disk-shaped rocks that differ in hardness or color from the surrounding host rock. They are commonly found in eroding shale or sandstone cliffs and along riverbeds. Collectors should look for nodules that have weathered out of their matrix.