sedimentary

Concretion in Shale

Siltstone/Shale with Siderite or Calcareous concretions

AI-generated identification · may be incorrect

Hardness: 3-4 (matrix 2-3). Color: Gray, tan, or brown. Luster: Dull/Earthy. Structure: Massive/Fine-grained with nodular inclusions. Specific gravity: ~2.5-3.0.

Hardness: 3-4 (matrix 2-3)
Color: Gray, tan, or brown
Luster: Dull/Earthy

Identified June 23, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (matrix 2-3). Color: Gray, tan, or brown. Luster: Dull/Earthy. Structure: Massive/Fine-grained with nodular inclusions. Specific gravity: ~2.5-3.0.

Formation & geological history

Formed through the precipitation of mineral cement within the spaces between sediment grains (shale or silt), often during early diagenesis in marine or lake environments. Many are from the Paleozoic or Mesozoic eras.

Uses & applications

Primarily used for geological study and fossil collecting; some concretions contain well-preserved fossils inside. Large deposits may be used for aggregate or fill.

Geological facts

Concretions are often mistaken for fossils, eggs, or meteorites. Some of the most famous concretions are the Moeraki Boulders in New Zealand.

Field identification & locations

Identify by a rounded or disc-shaped hardened mass sitting within softer layers of sedimentary rock. Common in shale cliffs, riverbeds, and coastal regions.