1. Unit 9 Lesson 3 How Can Rocks Be Classified?
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2. Unit 9 Lesson 3 How Can Rocks Be Classified?
Igneous Rock
Rock is a natural solid that is made of one or more minerals.
Rocks are classified by how they form.
There are three types of rocks: igneous, sedimentary, and metamorphic.
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3. Unit 9 Lesson 3 How Can Rocks Be Classified?
Igneous Rock
Igneous rock forms when melted rock, called magma or lava, cools and hardens.
Igneous rocks can form deep inside Earth as magma slowly cools.
Igneous rocks can also form on Earth’s surface when a volcano erupts and the lava cools.
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4. Unit 9 Lesson 3 How Can Rocks Be Classified?
Igneous Rock
When magma cools slowly beneath Earth’s surface, large mineral crystals form.
When lava at Earth’s surface cools quickly, mineral grains do not have time to grow, and so the crystals remain small.
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5. Unit 9 Lesson 3 How Can Rocks Be Classified?
Sedimentary Rock
Sedimentary rock forms from sediment, or particles of weathered rock, that gets cemented or glued together under pressure.
Sedimentary rock can contain fossils.
Fossils are the remains or signs of a living thing, such as a bone, shell, leaf imprint, or fossil footprint.
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6. Unit 9 Lesson 3 How Can Rocks Be Classified?
Sedimentary Rock
Some sedimentary rocks, such as rock salt and limestone, form through chemical processes when minerals dissolved in water come out of solution.
Limestone is often formed from the shells of sea animals. These shells, which are made of mineral calcite, are crushed and cemented together.
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7. Sedimentary Rock Describe how the sediment changes into rock.
Unit 9 Lesson 3 How Can Rocks Be Classified?
Sedimentary Rock
Describe how the sediment changes into rock.
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8. Unit 9 Lesson 3 How Can Rocks Be Classified?
Metamorphic Rock
A rock that forms when Earth processes change the texture and the mineral content of rock is called metamorphic rock.
Metamorphic rock can form from high pressure, high temperature, or a combination of both.
Metamorphic rock can also form when super-hot fluids come into contact with rock.
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9. Unit 9 Lesson 3 How Can Rocks Be Classified?
Metamorphic Rock
Mountains can form when two large pieces of Earth’s crust push against each other, causing rocks in the growing mountains to change.
Pressure builds up and rock layers may bend, twist, and break.
Over time, many of the rocks become metamorphic rocks.
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10. Unit 9 Lesson 3 How Can Rocks Be Classified?
The Rock Cycle
Any type of rock can become another type of rock. The continuous process of rock changing from one type to another is known as the rock cycle.
For example, after igneous rock is formed, weathering and erosion can break it down to form sediment which later forms rock.
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11. Unit 9 Lesson 3 How Can Rocks Be Classified?
The Rock Cycle
Metamorphic rock can be broken down in the same way to become sediment, which can be broken down, transported, and deposited to become new sedimentary rock.
Temperature and pressure can also transform any type of rock into metamorphic rock.
Any rock can be melted and cooled to form igneous rock.
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12. Unit 9 Lesson 3 How Can Rocks Be Classified?
Uses of Rock
Many monuments and statues, such as the Lincoln Memorial in Washington, D.C., are made of marble, a relatively soft metamorphic rock.
Toothpaste is made from several minerals that are extracted from rocks. These minerals have natural cavity-fighting properties.
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13. Unit 9 Lesson 3 How Can Rocks Be Classified?
Uses of Rock
Many old buildings and monuments, such as the Egyptian pyramids, are made of limestone. Today, limestone is used in many homes and office buildings.
Many building materials, such as cement and concrete, are made from rocks.
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