All the chemical, biochemical, and physical changes that sediments undergo from the time of deposition until the stage of metamorphism is reached. Diagenetic changes are gradational with metamorphism at elevated temperatures or pressures, and with atmospheric weathering effects when sedimentary rocks are exposed on the Earth's surface. Diagenesis commonly transforms sediments into sedimentary rocks and results in significant chemical and mineralogical changes. With increased burial, sands undergo grain rearrangement and compaction, mineral dissolution or replacement, and mineral precipitation as cements. Clays formed during weathering processes are transformed into illite, chlorite, and muscovite. Porous carbonate sediments consisting of unstable aragonite or magnesium-calcite are transformed to nonporous limestones composed of calcite. In spite of these profound changes, many features such as macroscopic sedimentary structures may be preserved in both detrital (sandstones and shale) and carbonate rocks. Diagenetic processes and products vary with original sediment composition and depositional environment, depth of burial (pressure and temperature), burial time, nature and movement of interstitial fluids, and physical, chemical, and biochemical processes.