DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Oolitic limestone rock. This section through a block of limestone shows ooids, or concentrically layered spherical grains. Ooids are mostly composed of carbonate minerals. They form when waves in warm and shallow water cause small grains of sediment to roll to and fro, collecting layers of mineral coating. This sample measures 33 millimetres tall.
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