Oolite. Light micrograph of a thin section through limestone showing ooliths. Ooliths are spherical bodies (seen here) formed by the precipitation of minerals, often carbonate, in concentric layers around a nucleus. Usually they are small, up to 2 millimetres in diameter. The calcium ground substance in which they are embedded is visible. Oolites are common in the Jurassic system of Britain. Some non-calcareous oolites are known, such as those formed from iron minerals. Magnification: unknown.
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