1. How Can Rocks Be Classified?
Unit 3 Lesson 4
How Can Rocks Be Classified?

2. Today’s Learning Goal
I will be able to explain the differences between igneous, sedimentary, and metamorphic rocks.
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3. Rocks and Minerals
Rocks and minerals are related because minerals create rocks.
Rock is a natural solid that is made of one or more minerals.
Rocks are classified by how they form.
There are three main groups of rock: igneous rock, sedimentary rock, and metamorphic rock.
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4. Igneous Rock
Igneous rock forms when melted rock, or magma, cools and hardens.
Magma can cool at different rates.
The way the magma cools determines what kind of igneous rock forms.

5. Igneous Rock
An igneous rock that cools slowly deep underground has large crystals.
An igneous rock that cools faster has smaller crystals.
An igneous rock that cools very quickly does not have crystals.

6. Igneous Rock
Igneous rocks cool so fast that they often are rough and have lots of bumps and holes.
The bumps and holes are caused when the rock cools so fast, that air bubbles are trapped inside the cooling rock.
Rocks that have very rough edges and lots of holes and air chambers will actually float in water. Pumice is an example of this kind of rock.

7. Sedimentary Rock
Rocks that form from sediments that are squeezed and cemented together are called sedimentary rock.
You can actually SEE the layers of sedimentary rock.
Sometimes traces of dead plants and animals called fossils are found in sedimentary rock.

8. Sedimentary Rock
Describe how the sediment changes into rock.

9. Metamorphic Rock
A rock that is changed by heat and pressure deep inside Earth is called a metamorphic rock.
Heat and pressure can change the way a rock looks and may even cause a rock’s minerals to change into other minerals.

10. Useful Rocks Metals are used to make cars, silverware, and jewelry.
Copper and gold are metals found in the ground that are mined out of rocks.
Obsidian was used by people long ago to make tools. Today it is used to make surgery tools.
Mining Copper
Mining Gold

11. Useful Rocks
Many old buildings and monuments are made of limestone. Today it is used in many homes and office buildings.
Many building materials, such as cement, concrete, and drywall, are made from rocks.
The Empire State Building in NYC is made of limestone.
Constitution Hall in Washington, DC is also made of limestone.

12. Useful Rocks
Did you know….that toothpaste is made from several minerals extracted from rocks?

13. Useful Rocks
Many statues and monuments are made of marble.

14. The Rock Cycle
The continuous process in which one type of rock changes into another type is known as the rock cycle. Any kind of rock can become any other kind of rock.

15. The Rock Cycle
The rock cycle also includes weathering, which means that the rock wears away over time.
Moving water, wind, and ice cause rocks to continuously wear away over time.
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16. REVIEW - Today’s Learning Goal
I will be able to explain the differences between igneous, sedimentary, and metamorphic rocks.
Can you?