Sedimentary Rock Formation

Biochemical Rocks

A sedimentary rock that was formed by organisms or contains the remains of organisms.

Chemical Rocks

Form when minerals crystallize directly from water.

Clastic Sedimentary Rocks

Geologists identify clastic rocks according to clastic size and shape. Sediment size alone cannot be used to determine the environment where a clastic rock formed. Some rocks, such as a sandstone, have a gritty texture that is similar to sugar. Geologists study the shape of clasts to help determine the environment where a rock formed.

Sedimentary Rock Identification

Sedimentary rocks are classified according to how they form. Sedimentary rocks form when sediments, rock fragments, minerals, or organic materials are deposited, compacted, and then cemented together. They also can form during evaporation.

Sedimentary Rock Formation

Sedimentary rocks can form in different environments through a series of natural steps. Pre-existing rocks are uplifted and weathered to for sediment. Then erosion, deposition, compaction, and cementation turn the sediment into solid rock. Younger sediment layers burry older sediment layers. Eventually, the old and young layers of sediment can be buried by even younger sediment deposits.

Clastic Rocks

Sedimentary rocks that are made up of broken pieces of minerals and rock fragments.

Clasts

The broken pieces and fragments.

Biochemical Sedimentary Rocks

The most common biochemical sedimentary rock is limestone. Marine organisms make their shells from dissolved minerals in the ocean. When the organisms die, their wheels settle not the sea floor. This sediment is compacted and cemented and forms limestone.

Compaction

The weight from the layers of sediments forced out fluids and decreases the space between grains.

Chemical Sedimentary Rocks

Water can become saturated with dissolved minerals. When this occurs, particles can crystallize out of the water and form minerals. Chemical sedimentary rocks often have an interlocking crystalline texture, similar to textures of many igneous rocks. Chemical sedimentary rocks are generally composed of one dominant mineral and are uniform in color.

Cementation

When minerals dissolved in water crystallize between sediment grains.