What is concretion?

concretion meaning in Soil Science terminology / glossary / dictionary is:
(i) A cemented concentration of a chemical compound, such as calcium carbonate or iron oxide, that can be removed from the soil intact and that has crude internal symmetry organized around a point, line, or plane. (ii) (micromorphological) A glaebule with a generally concentric fabric about a center which may be a point, line, or a plane.


reference: Soil Science Society of America