sedimentary

Sandstone Concretion

Septarian Concretion (Nodule)

AI-generated identification · may be incorrect

Hardness: 3-5 (depending on mineral cement); Color: Grey, tan, earthy; Luster: Dull/Earthy; Structure: Spheroidal, often displaying shrinkage cracks (septaria); Specific Gravity: ~2.5

Hardness: 3-5 (depending on mineral cement)
Color: Grey, tan, earthy
Luster: Dull/Earthy

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 3-5 (depending on mineral cement); Color: Grey, tan, earthy; Luster: Dull/Earthy; Structure: Spheroidal, often displaying shrinkage cracks (septaria); Specific Gravity: ~2.5

Formation & geological history

Formed by the precipitation of mineral cement within the spaces between sediment grains, often around a nucleus like a leaf or shell. Frequently found in shale and sandstone beds of various geological ages.

Uses & applications

Primarily of interest to geological collectors and educators; larger or more aesthetic septarian nodules are cut and polished for lapidary use and decor.

Geological facts

These are often mistaken for fossils, eggs, or meteorites due to their unnatural symmetry. The cracks visible on the surface suggest it may have a hollow or mineral-filled interior.

Field identification & locations

Identify by its rounded shape, distinct texture compared to surrounding rock, and characteristic 'turtle-back' cracking. Commonly found in eroded creek beds and sedimentary outcrops.