Dirt - Sediment - Sedimentary Rocks

How do sedimentary rocks form?

Sedimentary rocks are formed from particles of rocks that have been broken down by wind and water. When the little pieces are broken from the rocks, they are washed downstream and settle in the bottom of streams, rivers, and oceans.

 

 

The sediments keep piling up until there are many layers of sediments pressing down on top of each other. Over time, the bottom layers of the sediments turn into rocks that can be made out of almost any material found in nature. They are even made out of pieces of igneous rocks, metamorphic rocks, and other sedimentary rocks.

There are three types of sedimentary rocks. Clastic sedimentary rocks are formed by some sort of weathering. These rocks are moved around by waves, or flowing water and eventually stick together to form sedimentary rocks. Chemical sedimentary rocks are formed when water evaporates. When this happens, water is gets more concentrated as it dries up and the minerals in it start to precipitate out to make up the rocks. Biological sedimentary rocks form when plant and animal debris pressurize and build up.

 

Sedimentary rock examples and uses

Sandstone is a clastic sedimentary rock. Its grains are the size of sand.
Breccia is a clastic sedimentary rock. Its grains are gravel sized and it is made out of fragments of rocks and other minerals.
Rock salt is a chemical sedimentary rock. It is formed by the evaporation of salt water from oceans
Coquina is a biological sedimentary rock. It is made up of whole shells and broken pieces of shells.
Fossiliferous limestone is a biological sedimentary rock. It is made from calcite but has fossils in it. In this example, you can see fossils from shells.
Uses of Sedimentary Rocks
Alaskan Eskimos uses to use chert as tools and weapons.
Chalk is a type of limestone that all of you have seen before. Your teacher uses it to write on the blackboard at school!
Coal forms from plant debris in a swampy environment. This train is carrying coal, but some trains called Steam Engines use the coal for fuel. I hope you’re all being good this year, because you know that if you’re bad Santa brings you coal too!

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