1. Compaction: As layers of sediment accumulate, the weight of the overlying layers presses down on the lower layers. This pressure squeezes out water and air, causing the sediment particles to pack closer together.
2. Cementation: Dissolved minerals in the water that permeates through the sediment precipitate out and crystallize between the sediment grains. These minerals act as a "glue", binding the grains together and solidifying the sediment.
Common cementing minerals include:
* Calcite (CaCO3): Often derived from the breakdown of shells and other carbonate materials.
* Quartz (SiO2): Derived from the dissolution and re-precipitation of silica.
* Iron oxides (Fe2O3): Responsible for the red, brown, and yellow colors in some sedimentary rocks.
The type of cementing minerals present influences the rock's properties:
* Calcite cement results in a relatively soft, porous rock.
* Quartz cement produces a harder, denser rock.
* Iron oxide cement can make the rock colorful and resistant to weathering.
In addition to compaction and cementation, other factors can influence lithification:
* Temperature: Higher temperatures can accelerate the rate of cementation.
* Pressure: Greater pressure can enhance compaction and promote recrystallization of minerals.
* Time: Lithification is a slow process that can take millions of years to complete.
So, the next time you see a sedimentary rock, remember that it was formed by a long and complex process involving the burial, compaction, and cementation of sediment!
