Sesson 2: Lithification (Making Rock)

Key Idea

The journey from loose debris to hard rock involves a change in state. Sediment—which includes loose sand, pebbles, and organic remains—settles at the bottom of water bodies in flat layers. To become rock, these layers must undergo lithification.

This involves the physical squeezing of particles (compaction) followed by the chemical binding of those particles by minerals (cementation). Without these two steps, the sediment would remain loose mud or sand rather than becoming permanent sedimentary rock.

Key Idea

In a stack of sedimentary layers, gravity plays a crucial role. The overlying layers are heavy, pressing down on the material beneath them.

This pressure forces the sediment particles in the lower layers to pack closer together, eliminating empty spaces and squeezing out water. This process, called compaction, makes the layer denser and more solid, preparing it for the final stage of hardening.

Key Idea

Even after compaction, tiny gaps remain between sediment particles. Water flowing through these gaps carries dissolved minerals. As the water moves through, it leaves these minerals behind.

Over time, the minerals crystallize and harden, acting as a natural "glue" that binds the sediment particles to one another. This final step, known as cementation, locks the structure in place, completing the transformation into solid sedimentary rock.