In the Simple Ideal Model For The Evolution Of Sedimentary Rocks we said that if weathering, transportation, and sorting go to completion all that remains are three end member rock compositions. Siliciclastic Rocks Carbonate Rocks QUARTZ arenite SHALE LIMESTONE/DOLOMITE Limestones are not single composition rocks but a group of related rocks all composed of CaCO 3 and reacting with dilute HCl acid. Limestone [CaCO 3 ] is also chemically related to dolomite [CaMg(CO 3 ) 2 ]. Because all these rocks have CO 3 -in common they are called thecarbonates. The composition of most carbonates is derived from a combination of