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4.3: Lesson 4.2: Igneous Rocks

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Key Concepts

  • Formation of igneous rocks
  • Intrusive and extrusive igneous rocks
  • Composition of igneous rocks
  • Uses of igneous rocks

Lesson Objectives

  • Describe how igneous rocks form.
  • Describe properties of common igneous rocks.
  • Relate some common uses of igneous rocks.

Lesson Vocabulary

  • extrusive rock: Igneous rock that forms on Earth’s surface from rapidly cooling lava.
  • intrusive rock: Igneous rock that forms beneath Earth’s surface from slowly cooling magma.

Teaching Strategies

Introducing the Lesson

Tell students that one of the three major types of rocks is called “fire rock.” Ask them to guess which type of rock it is (igneous), and explain why it has that name (it forms from molten rock). Tell students they will learn more about igneous rock in this lesson.

Building Science Skills

Students can learn about igneous rocks with the hands-on activity at the URL below. In the activity, they will study samples of common igneous rocks (basalt, granite, pumice, and obsidian), model rates of cooling and relate them to crystal formation in the rocks, and identify the environments in which the rock samples formed.

http://www.pdesas.org/module/content/resources/13983/view.ashx

Activity

In this igneous rock activity, you can make pancakes to model the formation of igneous rocks—and students get to eat the “rocks” at the end of the activity! From the activity, students will learn to differentiate between intrusive and extrusive igneous rocks by texture. They will also learn why some extrusive rocks have holes and why both intrusive and extrusive rocks may vary in color.

http://www.learnnc.org/lp/pages/3688

Differentiated Instruction

Give visual and kinesthetic learners an opportunity to examine several igneous rock specimens that demonstrate important lesson concepts, such as intrusive and extrusive rocks and igneous rocks with a variety of different textures. Have them relate the features they are seeing and touching to the text in the lesson.

Enrichment

Have a few creative students collaborate on an illustrated poster showing a diversity of uses of igneous rocks. Display the poster in the classroom, and urge other students to examine it.

Science Inquiry

Students can actively model the formation of intrusive and extrusive igneous rocks with the kinesthetic game at the URL below. Students will learn how rate of cooling affects the type of rock that forms and how to classify igneous rocks based on texture.

http://www.nps.gov/brca/forteachers/randmact3.htm

Science Inquiry

Show the class one or more specimens of intrusive and extrusive igneous rocks. The intrusive specimens should have markedly larger crystals than the extrusive specimens. Call on volunteers to describe the features of the two rocks. Ask students to decide which rock formed under the surface and which formed on the surface. Have them explain their reasoning.

Common Misconceptions

A documented misconception held by middle school students is that all rocks are the same, and it’s hard to tell how they originated. Use actual rock specimens or photos to show students how igneous rocks differ from other types of rocks such as sedimentary rocks, and how intrusive and extrusive igneous rocks differ from each other. In both cases, relate the differences in rock features to the ways the rocks formed. For example, relate the coarser texture of intrusive igneous rock to slow cooling below Earth’s surface.

Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Earth Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 4.2 Quiz in CK-12 Earth Science for Middle School Quizzes and Tests.

Points to Consider

Do you think igneous rocks could form where you live?

Would all igneous rocks with the same composition have the same name? Explain why they might not.

Could an igneous rock cool at two different rates? What would the crystals in such a rock look like?

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