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Igneous Rocks

Igneous Rocks. Key Concepts. What geologic processes must happen to form igneous rock? How does the formation of magma affect igneous rocks? Where do they form? What are the types of igneous rocks? What are the physical/chemical properties of igneous rocks?

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Igneous Rocks

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  1. Igneous Rocks

  2. Key Concepts • What geologic processes must happen to form igneous rock? • How does the formation of magma affect igneous rocks? • Where do they form? • What are the types of igneous rocks? • What are the physical/chemical properties of igneous rocks? • What part do igneous rocks play in the rock cycle?

  3. Formation of Igneous Rocks • Forms when magma cools & hardens • Minerals crystallize • Identity is determined by the chemical composition of the minerals & texture • 3 factors that affect melting: temperature, pressure & presence of fluids

  4. How magma affects formation of igneous rocks… Partial Melting • Process by which different minerals in the rock melt at different temperatures. • Affects the composition of the magma Fractional Crystallization • Cooling process of magma where different minerals crystallize at different rates • Opposite of partial melting *Size of crystals is determined by the cooling rate of the magma

  5. Textures of Igneous Rocks • Classified according to where magma cools & hardens • 2 types: intrusive or extrusive • Determined by the size of crystals & cooling rate of magma

  6. Intrusive vs. Extrusive

  7. Intrusive • Form when magma cools deep inside the crust • Magma intrudes or enters into other rock masses beneath Earth’s surface • Cools & hardens slowly • Yield: coarse-grain rocks: large minerals • Example: granite

  8. Extrusive • Forms when lava cools at Earth’s surface (outside) • Cools & hardens rapidly…small crystals • Yield: fine-grain rocks: small minerals • Example: basalt & rhyolite

  9. Other Igneous Rock Textures • Porphyritic--Combination of both large & small crystals • Glassy texture—very few crystals • Vesicular texture—cools rapidly & gas bubbles cause holes

  10. Composition of Igneous Rocks • Mineral composition is determined by the chemical composition of the magma that formed the rock • 3 families • Felsic • Mafic • Intermediate

  11. Felsic Rock • Contains a large proportion of silica • Light-coloring • Main minerals: potassium feldspar & quartz • Examples: granite, rhyolite, obsidian, & pumice

  12. Mafic Rock • Contains lower proportions of silica • Rich in iron & magnesium • Main minerals: plagioclase feldspar & pyroxene • Dark colored • Examples: basalt & gabbro

  13. Intermediate Rocks • Lower silica content than felsic but more than mafic • Main minerals: plagioclase feldspar, hornblende, pyroxene, & biotite mica • Examples: diorite & andesite

  14. Where do Igneous Rocks form? Intrusive • Intrusions-when magma intrudes other rock masses & cools inside Earth • Batholiths & Stocks • Laccoliths • Sills & Dikes Extrusive • Extrusions-form on Earth’s surface • Volcano • Lava flows • tuff

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