Is this what geologists mean by the rock cycle?
Okay, maybe not. The rock cycle shows how any type of rock can become any other type of rock. The three rock types are joined together by the processes that change one to another.
The Rock Cycle
You learned about the three rock types: igneous, sedimentary and metamorphic. You also learned that all of these rocks can change. In fact, any rock can change to become any other type of rock. These changes usually happen very slowly. Some changes happen below Earth’s surface. Some changes happen above ground. These changes are all part of the rock cycle. The rock cycle describes each of the main types of rocks, how they form and how they change.
The Figure below shows how the three main rock types are related to each other. The arrows within the circle show how one type of rock may change to rock of another type. These are the processes that change one rock type to another rock type.
The Rock Cycle.
Processes of the Rock Cycle
There are three main processes that can change rock:
- Cooling and crystallization. Deep within the Earth, temperatures can get hot enough create magma. As magma cools, crystals grow, forming an igneous rock. The crystals grow larger if the magma cools slowly, as it does if it remains deep within the Earth. If the magma cools quickly, the crystals will be very small. When crystals form from magma it is called crystallization.
- Weathering and erosion. Water, wind, ice, and even plants and animals all act to wear down rocks. Over time they can break larger rocks into sediments. Rocks break down by the process called weathering. Moving water, wind, and glaciers then carry these pieces from one place to another. This is called erosion. The sediments are eventually dropped, or deposited, somewhere. This process is called sedimentation. The sediments may then be compacted and cemented together. This forms a sedimentary rock. This whole process can take hundreds or thousands of years.
- Metamorphism. This long word means “to change form.“ A rock undergoes metamorphism if it is exposed to extreme heat and pressure within the crust. With metamorphism, the rock does not melt all the way. The rock changes due to heat and pressure. A metamorphic rock may have a new mineral composition and/or texture.
An interactive rock cycle diagram can be found here: Rock Cycle (http://www.classzone.com/books/earth_science/terc/content/investigations/es0602/es0602page02.cfm?chapter_no=investigation)
The rock cycle really has no beginning or end. It just continues. The processes involved in the rock cycle take place over hundreds, thousands, or even millions of years. Even though for us rocks are solid and unchanging, they slowly change all the time.
crystallization: The formation of mineral grains from cooling magma.
erosion: The transport of weathered materials and sediments by water, wind, ice, or gravity.
metamorphism: A solid state change in an existing rock due to high temperature and/or pressure that creates a metamorphic rock.
sedimentation: The dropping of sediments into a deposit.
weathering: The chemical or physical breakdown of rocks, soils or minerals at Earth's surface.
- The three main rock types are igneous, metamorphic and sedimentary.
- The three processes that change one rock to another are crystallization, metamorphism, and erosion and sedimentation.
- Any rock can transform into any other rock by passing through one or more of these processes. This creates the rock cycle.
Use these resources to answer the questions that follow.
1. How do igneous rocks form?
2. What are the two types of igneous rocks and how do they differ?
3. What are metamorphic rocks?
4. How do metamorphic rocks form?
5. How do sedimentary rocks form?
6. List three examples of igneous rocks.
7. List three examples of sedimentary rocks.
8. What forms coal?
9. List three examples of metamorphic rocks.
10. Can an igneous rock become an igneous rock? Can a sedimentary rock become a sedimentary rock? Can a metamorphic rock become a metamorphic rock?
11. Draw an diagram of the rock cycle. Include the processes that transform rocks from one type to another.
1. What processes create igneous rocks?
2. What processes create metamorphic rocks?
3. What processes create sedimentary rocks?