Sedimentary Rocks Columbia University
Clastic Sedimentary Rocks. Clastic sedimentary rocks may first be classified according to their grain size. Claysized particles are too small to be seen with a microscope. Rock formed from claysize particles are called shale. Siltsized particles are visible with a microscope. Rock formed from these are called siltstone. Sandsized grains are visible to the naked eye and range from 1/16 mm to 2 mm. .