Lesson Plan - Get It!
What is your house made of? If you have stone, brick, marble, tile, sand, glass, or even metal in your house, you have some form of rock! Explore those plain old rocks in your yard and learn how to tell what kind is what!
Rocks can be found many places in creation.
They are under our feet, used to build our homes, and make up the roads we drive along. These rocks are classified based on how they form. There are three types of rocks: igneous, sedimentary, and metamorphic.
If you have not yet studied, or need to review, the previous Related Lessons in the Rocks and Minerals series, find them in the right-hand sidebar.
Igneous rocks are formed when magma from under Earth’s surface cools and solidifies. Igneous rocks can form above or below the ground.
Since they are created from magma, they often have small bubbles or holes that result from air in the rock as it cools. These rocks usually look the same all the way around.
Some have large particles in the rock, like granite, but many do not have visible particles.
Igneous rocks can also be glassy, like obsidian, pictured below:
Sedimentary rocks form when sediment builds up in an area. Think about how dust settles on untouched surfaces in your house. Sedimentary rock forms in a similar way, with layers forming on top of one another. Sometimes you can even see the layers in the rock.
Other sedimentary rocks do not have layers that you can see, but you can feel large pieces of material in the rock.
These rocks are usually pretty soft, and break apart easily.
Metamorphic rocks have been exposed to high amounts of heat and intense pressure. What would happen to a crayon if you heated it and pushed it into a ball? It might change shape! Metamorphic rocks do the same thing! If a metamorphic rock forms from a sedimentary rock, you might be able to see the layers, even after the heat and pressure. Can you see the layers in the metamorphic rock below?
Rocks can change into another type of rock by moving through the rock cycle. Check out the Related Lesson again to review more about how rocks change through the rock cycle. Rocks are constantly being recycled into new substances. As rocks break apart, they move as sediment, eventually becoming sedimentary rocks. Once buried, they may be exposed to heat and pressure, changing into metamorphic rock.
So you see, the characteristics of each type of rock are based on the way that they form on Earth.
Discuss what you have learned about rock identification with a parent or teacher before testing your knowledge in the Got It? section with a drag-and-drop interactive.