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Earth Science Chapter 8: Rocks Lesson 2: Igneous Rocks • Learning Targets • By the end of the lesson, I will be able to: 1. Explain how igneous rocks form 2. Compare intrusive and extrusive igneous rocks 3. Identify samples of igneous rocks • Pg 181 Textbook How igneous rocks form • Deep below earth’s surface temperatures reach around 1,400 degrees C • Minerals melt to form magma (hot liquid rock formed inside the earth) • Magma sometimes rises through gaps in the surface of the earth • The rock cools thus forming igneous rock Intrusive Rocks • Igneous rock that forms underground is called intrusive rock • Rock forms slowly (large crystals due to this) • The size of the minerals crystals in an igneous rock are called the rock’s texture • Intrusive rocks have a course-grained texture • Most common is granite • Can be any color (mixture of minerals) Extrusive rocks • When magma reaches the earth’s surface it is called lava • Lava cools and forms extrusive rock • Cools quickly so does not have many crystals (fine-grain texture) • Most common is basalt • Volcanic eruptions • Glassy texture Recap • Learning Targets • By the end of the lesson, I will be able to: 1. Explain how igneous rocks form 2. Compare intrusive and extrusive igneous rocks 3. Identify samples of igneous rocks • Assignment