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

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.