Sedimentary rocks are formed from deposits of pre-existing rocks or pieces of once-living organism that accumulate on the Earth's surface. If sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock. These rocks often have distinctive layering or bedding and create many of the picturesque views of the desert southwest. Sedimentary rocks are classified into three groups: clastic, biologic, and chemical.
Cementation: The process by which clastic sediments become lithified or consolidated into hard, compact rocks, usually through deposition or precipitation of minerals in the spaces among the individual grains of the sediment.
Compaction: The process of consolidating fine-grained sediments into rock.
Lithification: The conversion of loose sediment into solid sedimentary rock. Several processes, including compaction of grains, filling of spaces between grains with mineral cement, and crystallization act to solidify sediment.