oolith

noun Geology.

1. any of the component concretions of a piece of oolite.

noun

1. any of the tiny spherical grains of sedimentary rock of which oolite is composed

1. A small, round grain consisting of calcium carbonate, silica, or dolomite. Ooliths have concentric layers that form around a nucleus, such as a shell fragment, a sand grain, or a pellet of alga. They typically have diameters of 0.25 to 2 mm. Ooliths usually form by inorganic precipitation.