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Sedimentary Rocks Lesson for Kids: Definition & Facts

Instructor: Debra Patuto

Debra has taught at elementary levels and has an M.ed with certification in elementary education and special education

You can find sedimentary rocks all along Earth's surface--even in your own backyard. Let's find out what sedimentary rocks are and learn how they are made.

What are Sedimentary Rocks?

Let's think about how a peanut butter and jelly sandwich is made: a bottom layer of bread, then a thick layer of peanut butter, followed by jelly on top of the peanut butter, and then another piece of bread on top. Press down, and there you have it--a peanut butter and jelly sandwich!

Sedimentary rocks are made from layers just like a peanut butter and jelly sandwich, and they make up a large part of Earth's rocky surface. You might not be able to see them forming right away, but every time there is rain, snow, or a large gust of wind, layers upon layers are being squashed down on top of one another, and over time, sedimentary rocks are made.

What are Sedimentary Rocks Made of?

Sedimentary rocks are made when erosion, or the breaking down of the land around you, takes place. The small pieces of land that break down are called sediment. The sediment can be grains of sand, mud, pebbles, minerals, fossils or plants.

The sediment travels around by wind or bodies of water until it finally settles. Over time, layers of sediment pile up on top of one another. Eventually, the layers harden and turn to rock.

This picture shows the layers that have been compressed down over time in sedimentary rock.
layers in sedimentary rock

The Three Types of Sedimentary Rocks

Clastic sedimentary rocks are formed when big rocks are broken down into little ones. This process happens on Earth's crust and is often due to temperature changes. Cool nights and hot days can cause rocks to expand and contract, which can then cause rocks to crack and break into pieces. The small pieces then get compressed together over time. Examples of clastic sedimentary rocks are breccia, conglomerate, sandstone, siltstone and shale.

Chemical sedimentary rocks are formed when dissolved minerals come out of water. These rocks form in oceans, lakes, caves and hot springs and have a crystal-like shape to them. It is common to find marine life fossils in these rocks. Examples include rock salt, iron ore, limestone and flint.

Organic sedimentary rocks form when leaves, roots, plants and animal materials are broken down and then compressed over time. Very often, you will find that these rocks are black, soft and contain fossils. Coal is a good example of an organic sedimentary rock.

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