Ooids

Ooids are small, rounded sedimentary grains composed of concentric mineral layers, typically calcium carbonate, that form in shallow, warm, and wave-agitated waters. They develop through a process called accretion, where mineral-rich solutions deposit new layers around a nucleus, often a tiny particle or shell fragment. Over time, these layers grow uniform and smooth, creating ooids ranging from tiny grains to several millimeters in size. Ooids are common in marine environments like warm reefs and lagoons and are important in forming certain sedimentary rocks, such as oolitic limestone.