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A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. [1] Concretions are often ovoid or spherical in shape, although irregular shapes also occur.
They commonly occur as concretions in mudstones and siltstones. Pyrite and marcasite (FeS 2) are sulfide minerals and favor reducing conditions. They are the most common in fine-grained, dark colored mudstones. Hematite (Fe 2 O 3) is usually the pigment in red beds and requires oxidizing conditions.
The soil matrix is the solid phase of soils, and comprise the solid particles that make up soils.Soil particles can be classified by their chemical composition as well as their size.
A concretion is a volume of sedimentary rock in which a mineral cement fills the porosity (i.e. the spaces between the sediment grains). The image shows a Sandstone Concretion in the wall at the beach of Año Nuevo State Reserve. This concretion was too high in the wall to place a ruler, but I estimate it to be about 400 mm long.
These concretions occur in the black shale in the lower part of the Kettle Point Formation. Because the concretions are so much harder than the enclosing weakly indurated shale, they readily weather out of the shale along the shoreline and are incorporated into the rubble mantling the lake bottom adjacent to the outcrop.
An enterolith is a mineral concretion or calculus formed anywhere in the gastrointestinal system. Enteroliths are uncommon and usually incidental findings but, once found, they require at a minimum watchful waiting. If there is evidence of complications, they must be removed.
The most striking aspect of the boulders is their unusually large size and spherical shape, with a distinct bimodal size distribution. Approximately one-third of the boulders range in size from about 0.5 to 1.0 metre (1.6 to 3.3 ft) in diameter, the other two-thirds from 1.5 to 2.2 metres (4.9 to 7.2 ft).
Concretions are sometimes thought to be fossils, and occasionally one contains a fossil, but are generally not fossils themselves. Chert or flint nodules in limestone can often take forms that resemble fossils.