Oolite

Oolite is a type of sedimentary rock, usually limestone, made up of ooids cemented together. An ooid is a small spherical grain that forms when a particle of sand or other nucleus is coated with concentric layers of calcite or other minerals. Ooids most often form in shallow, wave-agitated marine water.

Just as oolitic limestones form from calcite ooids, dolomite and other rocks can be formed from ooids coated with other minerals. Oolitic limestones, particularly of Pennsylvanian age, are found at or near the surface in the eastern third of Kansas.