Clastic sedimentation is the type we just talked about, where there is weathering, erosion, transportation, deposition, and finally lithification. Clastic sediment has a wide range of sizes. The different sizes go from clay, which is 1/256th of a millimeter, to boulders, which are larger than 256 mm or 10 inches in diameter. In decreasing size, you have boulders, cobble, pebble, sand, silt, and then clay. If you consolidate the different kinds of sediments, you'll get various kinds of rocks out of them. Conglomerate or breccia comes from things that are pebbles or bigger. Sand makes sandstone and silt makes siltstone. Clay makes mudstone, shale, or claystone.
NAMING SEDIMENTARY ROCKS As we learn to name sedimentary rocks in this section, keep in mind that the size matters and the way the sediment came together matters. Starting with clastic rocks, you get these: •
Shale – this is dark-gray rock made from clay. You can't see these without a strong microscope.
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Siltstone – the pieces here are easier to see with a microscope. Notice the erosion of these rocks as siltstone in figure 37:
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