The mineralogy and textures of sedimentary carbonate rocks suggest two stages of diagenesis. The stabilization of skeletal fragments from aragonite, high magnesian calcite and calcite, to calcite is the first stage and generally pre-compactive grain fracture. The formation of cements and consequent reduction in porosity is the second stage and is generally post compactive grain fracture. Both stages involve reaction and equilibration with pore waters. Stable isotopes and trace element ratios indicate compositional variations between rain water and marine brines for these fluids. The role of organic reactions and clay minerals is important. Pressure solution may occur at any stage and varies from grain to grain to through rock stylolites.