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Earth Materials
Minerals | Rocks

Out of Solution

Concretions form within parts of already deposited sediment layers in which mineral cement, carried by groundwater, fills the spaces between the sediment grains before the rest of the sediment is hardened into a sedimentary rock. They are made of the same material as their host sediment but are cemented by harder minerals. Being more firmly cemented than the enclosing sediment, concretions weather out in various shapes.

Sand Crystals