Cement is the material that bonds rock grains, soil particles and structural surfaces. In general, the cement content of clastic rocks does not exceed 50%. Cement has two general definitions: (1) the chemical sediment in clastic rock, excluding the clastic grains and the matrix; and (2) chemically precipitated sediment that fills the pores between the clastic grains, excluding clay and other fine materials. The latter interpretation is more common. Typical cements include siliceous, calcareous, ferrous, phosphorous, pelitic and soluble salts.