Calcite cement in an ooid-rich limestone; Carmel Formation, Jurassic of Utah.

Cementation is what makes rocks solid. It is the process where grains of sediment get stuck together. It is a chemical process, and the cement is a precipitate which crystallises in the spaces between the matrix of grains. Silica (SiO₂) and calcium carbonate (CaCO₃) are the most common types of cement.