Putting It Together: Rocks and the Rock Cycle


In this section, you learned the following:

  1. The three rock types and how they are classified
  2. How each of the different rock types form
  3. The techniques geologist use to identify different rocks
  4. How to use these techniques to identify common rocks
  5. How the rock cycle works


In the rock cycle, illustrated in figure 1, the three main rock types—igneous, sedimentary, and metamorphic—are shown. Arrows connecting the three rock types show the processes that change one rock type into another. The cycle has no beginning and no end. Rocks deep within the Earth are right now becoming other types of rocks. Rocks at the surface are lying in place before they are next exposed to a process that will change them.

Representation of the rock cycle in a rough circle. Metamorphic rocks lead to erosion or melting. Melting leads to magma, which leads to crystallization (freezing of rock), which leads to igneous rocks. Igneous rocks lead to metamorphic rocks, melting, or to erosion. Erosion leads to sedimentation, which leads to sediments and sedimentary rocks. Sedimentary rocks leads to erosion or tectonic burial and metamorphism. Tectonic burial and metamorphism leads to metamorphic rocks.

Figure 1. The Rock Cycle.

The rock cycle is a continuous and dynamic cycle that has no starting or stopping point and no set progression. Rocks can move through different paths within the cycle. The rock cycle explains how each rock type forms and the processes involved. We saw how the processes within the cycle influence everything from soil formation to recording the history of the Earth to the role deformation plays in rocks. It is easy to see how the rock cycle influences our dynamic and ever changing earth.


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