DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Oolites are small (O 0, 5 to 3 mm), concentrically layered, spherical grains composed of limestone or other carbonate materials. Oolites form by the gentle rolling to and fro of small grains, like sand or shell fragments, by wave action on the bottom of warm and shallow marine waters. This rolling allows for the precipitation of calcium carbonate in a thin layer all around such grains. This sample is from glacial debris in moraine deposits accumulated during the Pleistocene Ice Ages in the north Netherlands. The boulders and coarse debris in these deposits are mostly derived from Paleozoic rocks in Scandinavia.
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