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 * Read: ** Review introductory material about rocks. What is the difference?
 * The terms //rock// and //mineral// are often lumped together. Unfortunately, people often assume these words mean the same thing. Rocks and minerals are, in fact, different.
 * Minerals are pure substances. They are made up of only one thing. A mineral is a naturally-formed solid with a definite chemical composition and crystal structure. The properties of a mineral do not change over time.
 * Rocks, on the other hand, are mixtures. In other words, rocks can be made up of many things. Rocks are typically made up of two or more different minerals. The properties of a particular rock depend on the properties of all of the minerals it is composed of. Change one mineral and you change the properties of the rock.

How many types of rocks are there?
 * A rock is classified into one of three categories — //igneous//, //metamorphic//, or //sedimentary// — depending on how it formed.

What happens to them?
 * Have you ever thought about what happens to a rock after it has formed? Does an igneous rock always remain an igneous rock? What about sedimentary and metamorphic rocks? What happens to them?
 * Some rocks stay buried beneath the earth after they form and can remain the same for billions of years. If something happens to push the rock toward the earth's surface, the rock will probably undergo some drastic changes. These changes can be so dramatic that the rock might even be transformed from one type to another. Through this Web Inquiry, you will learn how these changes occur.