sedimentary

Concretion

Sedimentary Concretion

Variable hardness depending on composition; earthy colors (brown, tan, gray); dull luster; irregular, nodular, or bulbous shape; no distinct cleavage.

Identified July 24, 2026More sedimentary →

Explore Concretion in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Variable hardness depending on composition; earthy colors (brown, tan, gray); dull luster; irregular, nodular, or bulbous shape; no distinct cleavage.

Formation & geological history

Formed in sedimentary rock by the localized precipitation of mineral matter around a nucleus, often during early diagenesis.

Uses & applications

Primarily collected as curiosities by rockhounds; no major industrial value.

Geological facts

Concretions can sometimes contain well-preserved fossils at their centers, acting as protective nodules. They are often mistaken for meteorites or dinosaur eggs due to their unusual shapes.

Field identification & locations

Identified by their distinctive rounded, nodular, or botryoidal shapes that stand out from the surrounding host rock. Commonly found in shale, sandstone, or mudstone deposits.