Lithification is the process by which sediment turns into hardened rock. There are three ways in which lithification can occur. These processes are called compaction, recrystallization and cementation.
Compaction is a process of lithification that works for finer particles only. Compaction occurs when particles such as clay minerals are compressed. Coarser particles are not able to be hardened with this process because compression does not make them stick together.
Minerals such as limestone and aragonite can harden through the process of recrystallization. These minerals are easily dissolved in water, and the crystals that form from those dissolved minerals are much harder than the original substances.
Cementation is the process where coarser grain sediments become hardened rock. Water fills into the empty space between the particles, and the ions in the water create new crystalline formations among the sediments. When the water evaporates, the sediment eventually seals and hardens, leaving behind a solid piece of rock.
The creation of new minerals during the cementation process is an example of authigenesis. Authigenesis is a term that describes a process in which new minerals are created inside a rock, or that the deposited minerals react and combine with the minerals already present in the rock or sediment.