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Chart showing  classification of sediment sizes Sediment is the word geologists use for loose pieces of minerals and rock. Of course, pieces of rock come in all sizes so we have developed a way to classify them. The chart on the left shows we use for each grain size. Most of the names are ones you already use; sand, boulders, and clay, for example. The illustrations of sand and pebbles are shown at their actual sizes. Unfortunately silt and clay are smaller than a single pixel on your computer screen, so they don't show up well here! Cobbles and boulders are another problem - they are too big to fit on your screen!

actual size comparison of pebbles Metric system chart
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