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Igneous Rocks

Igneous Rocks. How do igneous rocks form?. From the crystallization of magma. Magma can cool in two places. On the surface of the Earth ( Extrusive igneous rock) Crystal or grain size? Ex= rhyolite Below the surface of the Earth ( Intrusive igneous rock)

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Igneous Rocks

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  1. Igneous Rocks

  2. How do igneous rocks form? • From the crystallization of magma

  3. Magma can cool in two places • On the surface of the Earth (Extrusive igneous rock) Crystal or grain size? Ex= rhyolite • Below the surface of the Earth (Intrusive igneous rock) Crystal or grain size? Ex= granite

  4. Cross-cutting

  5. As we move closer to the center of the Earth, what happens to: • Heat? • Pressure? • Melting Point?

  6. What factors influence the formation/composition of magma? • Temperature • Heat • Pressure • Water content • Mineral content

  7. Partial Melting

  8. Fractional Crystallization

  9. Bowen’s Reaction Series

  10. Classifying Igneous Rocks • Felsic: light-colored, with high silica content. Contain quartz and feldspars (orthoclase and plagioclase) Ex: granite • Mafic: dark-colored with lower silica content. Rich in Fe and Mg. Contain plagioclase, biotite, amphibole, pyroxene. Ex: gabbro • Ultramafic: low silica and very high Fe and Mg. Formed by fractional crystallization of olivine and pyrene. Ex: peridotite and dunite.

  11. Look at GRAIN SIZE to help identify igneous rocks • Extrusive rocks always cool _________________, so they have _______________ crystals. Ex: pumice, obsidian, rhyolite • Intrusive rocks cool ___________________, so they have ______________ crystals. Ex: gabbro, basalt

  12. Pegmatite • A vein of extremely large-grained minerals (quartz, etc.)

  13. What is a kimberlite? • A rare, ultramafic rock that contains diamonds • Forms only under very high pressure, then intrudes rapidly towards surface of the Earth • Named for Kimberly, • South Africa

  14. The Kimberly Laws • Laws passed in 2003 that regulate the sale and trade of diamonds • Laws attempt to eliminate the sale of conflict diamonds (diamonds whose sale is used to fund warfare) • Named for Kimberly, South Africa, where the first major diamond mines originated

  15. Geography of Africa

  16. Kimberly diamond mine

  17. Harper’s WeeklyNew YorkNovember 19, 1870

  18. Mining for alluvial diamonds in Sierra Leone, 2007

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