Sedimentary [edit]. Sedimentary breccia is a type of clastic sedimentary rock which is made of angular to subangular, randomly oriented clasts of other sedimentary rocks. A conglomerate, by contrast, is a sedimentary rock composed of rounded fragments or clasts of pre-existing rocks.Both breccia and conglomerate are composed of fragments averaging greater than 2 millimetres (0.079 in) in size.edimentary breccia is a type of clastic sedimentary rock which is made of angular to subangular, randomly oriented clasts of other sedimentary rocks.