SEDIMENTARY ROCKS: A QUICK INSIGHT Sedimentary rocks are one of the major rock types that make up the Earth’s lithosphere. They are the most widespread, covering about 75% of the Earth’s surface. What makes sedimentary rocks unique is their layered appearance. This is because they form through diagenesis, the changes that occur to sediments after deposition, during lithification, and before metamorphism. The process of sediment formation involves: Weathering (physical and chemical breakdown of r