Template:POTD/2011-04-24

Picture of the day

Concretions on Bowling Ball Beach in Mendocino County, California. A concretion is a volume of sedimentary rock in which a mineral cement fills the spaces between the sediment grains, usually forming an ovoid or spherical shape. This normally occurs early in the burial history of the sediment, before the rest of the sediment is hardened into rock.Photo: Mila Zinkova