Concretion [ TOP-RATED × Checklist ]

A concretion is a hard, compact mass of mineral matter that forms within sedimentary rock or soil. While often mistaken for dinosaur eggs, fossils, or meteorites, they are distinct geological features formed by the selective precipitation of minerals from groundwater. How Concretions Form

: Because concretions are harder than the surrounding rock, they often remain after the softer host rock has weathered away, creating dramatic landscape features. Common Types and Compositions concretion

Concretions grow from the inside out, typically starting with a nucleus. This process, known as diagenesis, occurs early in the burial history of sediment. A concretion is a hard, compact mass of

: Groundwater rich in minerals (like calcite or iron) reaches a point of saturation and begins to solidify. Common Types and Compositions Concretions grow from the

: These minerals fill the pore spaces between sediment grains, acting as a "natural glue" that binds the mass into a hard rock.