As a class we have been studying rocks. So far we have done the rock cycle there are three different rocks named Sedimentary and igneous and metamorphic . So some of us has brought some of these types of rocks to class to have a look at here is a definition of the rocks sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed. Sedimentary. Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material.