For sediments to become sedimentary rocks, they need to be lithified:
Compaction: As sediments are buried, weight of overlying material compresses them, reducing void space and expelling water. Bonding of clay particles, if present, helps stick the sediments together.
Cementation: Compounds dissolved in water precipitate in remaining void space and bond particles together.
Crystallization: New minerals form and bond together at higher pressures and temperatures. (Gradual transition into metamorphism.)
