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Concretion identification and geology

A hard, compact mass of mineral matter formed within sedimentary rock by the localized precipitation of cementing material usually calcite, silica, pyrite, or iron oxide around a nucleus such as a fossil, shell, or grain. Concretions grow within the sediment during or after deposition and are typically spherical, ellipsoidal, or irregular in shape. They are often more resistant to weathering than the surrounding rock and may weather out as isolated boulders. Field: sedimentology. Example: The Moeraki Boulders of New Zealand are large spherical calcite concretions up to 2.2 m in diameter that formed within Paleocene mudstone and have been exposed by coastal erosion.. Related terms: Nodule, Diagenesis, Cementation, Septarian.

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:19:41.970235+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Concretion mean in geology?
A hard, compact mass of mineral matter formed within sedimentary rock by the localized precipitation of cementing material usually calcite, silica, pyrite, or iron oxide around a nucleus such as a fossil, shell, or grain. Concretions grow within the sediment during or after deposition and are typically spherical, ellipsoidal, or irregular in shape. They are often more resistant to weathering than the surrounding rock and may weather out as isolated boulders.
What is an example of Concretion?
The Moeraki Boulders of New Zealand are large spherical calcite concretions up to 2.2 m in diameter that formed within Paleocene mudstone and have been exposed by coastal erosion.
Which earth-science field uses the term Concretion?
Concretion is used in sedimentology.
Which terms are related to Concretion?
Related terms in this reference are Nodule, Diagenesis, Cementation, Septarian.

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