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 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 concretion
: A central point—like a leaf, shell, bone, or even a human artifact—attracts dissolved minerals. Concretions grow from the inside out, typically starting
: Groundwater rich in minerals (like calcite or iron) reaches a point of saturation and begins to solidify. While often mistaken for dinosaur eggs, fossils, or
: These minerals fill the pore spaces between sediment grains, acting as a "natural glue" that binds the mass into a hard rock.