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Earth’s Surface: Chapter 3 Section 2

Earth’s Surface: Chapter 3 Section 2. Objectives: 1. Explain why igneous rocks that formed at Earth’s surface are different from those formed within Earth 2. Recognize why silica content is important in classifying igneous rocks 3. Explain why igneous rocks can make long lasting landforms

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Earth’s Surface: Chapter 3 Section 2

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  1. Earth’s Surface: Chapter 3 Section 2 • Objectives: • 1. Explain why igneous rocks that formed at Earth’s surface are different from those formed within Earth • 2. Recognize why silica content is important in classifying igneous rocks • 3. Explain why igneous rocks can make long lasting landforms • 4. Analyze how cooling time affects crystal size.

  2. Magma and Lava Igneous rocks form from molten rock The deeper you go in the Earth, the hotter it gets. Deep in the Earth temp. are hot enough to melt rock (1400 – 2300 degrees Fahrenheit) Molten rock inside the Earth is called magma Molten rock at the surface of the Earth is lava Igneous rocks are classified by their mineral composition and the size of their mineral crystals

  3. Origin of Igneous Rocks • There are two main types of igneous rocks • 1. Intrusive: Forms when magma cools within Earth Ex. Granite, Gabbro • 2. Extrusive: Forms when lava cools on surface Ex. Rhyolite, Pumice, Basalt Granite Gabbro Pumice Rhyolite Basalt

  4. Origin of Igneous Rocks • Intrusive igneous rocks can reach the surface in different ways. 1. They may be pushed up when mountains form. 2. Water and wind can break apart and carry away surface rocks. Allowing deeper rocks to be revealed

  5. Textures of Igneous Rocks • Texture: the size of a rocks mineral crystals • The texture of an igneous rock depends on how quickly the magma or lava cooled • Intrusive Igneous Rocks: Will have large mineral Crystals because: • 1. Interior of Earth is very hot • 2. High temp. allow magma to cool slowly • 3. Slow cooling allows time for large crystals to form

  6. Intrusive Igneous Rocks Granite Diorite Gabbro Pegmatite

  7. Textures of Igneous Rocks • Extrusive Igneous Rocks have very small crystals because: • 1. Surface of Earth is cooler than the interior • 2. Lower temp. cause lava to cool quickly • 3. No time for large crystals to form • Igneous rocks may have both small and large crystals • These rocks formed from magma that started cooling inside the Earth and then erupted onto the surface. • Large crystals grew as magma cooled slowly. Small crystals grew as the lava cooled quickly.

  8. Extrusive Igneous Rocks Rhyolite Pumice Obsidian Basalt

  9. Composition of Igneous Rocks Most igneous rocks are made up of silicate minerals Geologists classify igneous rocks based on how rich it is in silica Silica is compound that contains oxygen and silicon Igneous rocks with high levels of silica are typically light in color (rhyolite) Igneous rocks with low levels of silica are typically dark in color (gabbro, basalt)

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