Geology Mastery Check #1 - Types of Rocks
Rocks can be classified into 3 different categories. They are divided into these categories according to how they form.
Igneous rocks
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Sedimentary rocks
Sedimentary rocks form when sediments are deposited and then compressed together to form a rock. Sediments can be any of the following:
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Metamorphic rocks
Metamorphic rocks are rocks that have been changed through heat and pressure (see picture #1). When rocks heat up they are better able to be changed (kind of like when you heat up a starburst, it is easier to stretch and compress). The rocks don't heat up enough to melt though. When rocks change through heat and pressure, it is called deformation. Deformation happens deep in the Earth where there are hotter temperatures and higher pressures (picture #2). Large plates of the Earth can collide and create high pressure that deform rocks. This is what is happening in picture #3. Here are some examples of metamorphic rocks:
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The Rock Cycle
The minerals that make up rocks are constantly being cycled from one form of rock to another. This is called the rock cycle. This cycle happens because of energy that causes rocks to change. There are two main sources of this energy. The energy needed to melt rocks, heat them up and deform them through pressure comes from the heat inside the Earth. The energy to weather rocks and transport sediments comes from the sun. The sun evaporates water, which goes into the air, falls to the Earth as rain or snow, and then creates rivers or glaciers. The diagram on the right represents the rock cycle.
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