How Are Sedimentary Rocks Formed?

Sedimentary rocks are formed from preexisting rock through the combined processes of weathering, transportation, deposition, compacting and cementation. The entire series of processes is known as lithification, and the weathering portion of the process can be either mechanical or chemical. The chemical weathering process involves the preexisting material being transported as a solute or in the form of a new mineral, while the mechanical process transports the material as solid particles.

The preexisting material is broken down by the forces of erosion, weather, water-wedging, root-wedging or abrasion. The particles are then transported by water, wind or glaciers to a new location, the place of deposition, where they arrive in the form of sediment. As the sediment grows layer upon layer, the pressure on earlier deposits causes them to become compacted. The compacted sediment is eventually formed into new rocks during the final cementation stage.