A sedimentary rock is a layered rock that is formed from the compaction, cementation, and the recrystallization of sediments.

Compaction is the squeezing together of layers of sediment due to the great weight of overlying layers of rock. This squeezing of the layer results in reducing the thickness of the original layer. When the layers are reduced in thickness the pore spaces around the sediments are also reduced, which leads to a tighter packing of the layers.

Cementation is the changing of sediment into rock by filling spaces around the sediments with chemical precipitates of minerals. binding the sediments, and forming solid rock. Calcite and silica are common minerals that cement the sediments together.

Recrystallization is the third way that sedimentary rocks are formed. Recrystallization is the formation of new mineral grains that are larger than the original grains. As the sediments recrystallize they arrange themselves in a series of interlocking crystals that connect the other grains together into a solid rock.

The photo to your left shows layers of sedimentary rocks that were deposited in flat horizontal layers. These layers were then uplifted and bent by mountain building.

Click on the "Next" button to learn about this type of sedimentary rock.