An Oolite (or an oolith) is a sphere consisting of several concentric layers of calcite (a form of calcium carbonate) that was created by precipitation in the supersaturated warm waters of shallow tropical seas. The term may also be applied to an oolitic rock (a rock formed from many compressed oolites).
Oolites are formed when a nucleus, typically a sand particle or shell fragment, accumulates a layer of calcite around it as currents roll it around on the sea bed. From time-to-time the growing oolite becomes buried beneath the surface, allowing the accumulated calcite to consolidate, with a fresh layer accumulating each time it returns to the surface. Oolites may grow up to 2mm in diameter (1/12 of an inch).
Limestone is a sedimentary rock composed principally of calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite).
Limestones may vary greatly in texture and porosity from coquina, which is a matrix of oyster shells loosely cemented by calcite, to ooliticlimestones and microcrystalline limestones whose structures are so fine that they can be seen only under magnification.
Ooliticlimestone consists of substantial amounts of "oolites" or "ooliths." Oolites are small spherical or sub-spherical grains of concentric calcite.
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