An example of detrital rock is a sandstone. It is formed by the disintegration of pre-existing rocks like granitic type rock for example into its constituent grains, by transport and deposition and then burial and compactionl An organic sedimentary rock is like coal which forms from the accumulation of dead plant life and its conversion into carbon first to lignite then to various types of coal.like bituminous and anthracite. A chemical rock can form by evaporation such as deposts of halite and sylvite ie NaCl and KCl, or limestone by the accumulation of hard shells of marine organisms with alot of calcium carbonate,.