Where is concretion from?

Concretions are typically formed in sedimentary rocks and occur when minerals precipitate from water, often in the presence of organic materials or other particles. They can develop in various environments, including riverbeds, lakes, and ocean floors, where sediment accumulates. Over time, these minerals crystallize around a nucleus, leading to the formation of rounded, compact masses. Common minerals involved include calcite, silica, and iron oxides.