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Earth Systems 3209

Earth Systems 3209. Reference: Chapters 2, 3, 6, 7; Appendix A & B. Unit: 3 Earth’s Materials. Unit 3: Topic 3.2. Classification of Igneous Rocks (Composition). Focus on . . . identifying the different compositions of Igneous rock.

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Earth Systems 3209

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  1. Earth Systems 3209 Reference: Chapters 2, 3, 6, 7; Appendix A & B Unit: 3Earth’s Materials

  2. Unit 3: Topic 3.2 Classification of Igneous Rocks (Composition) Focus on . . . • identifying the different compositions of Igneous rock. • relating Bowen's reaction series to mineral composition. • identifying and explaining how different Igneous rocks can have the same composition.

  3. Classification of Igneous Rocks: • Igneous rocks are further classified according to: • 1. Texture • Describes the appearance of an igneous rock, based on the size, shape and arrangement of interlocking crystals. • 2. Mineral Composition • Is the mineral makeup of an igneous rock based on the chemical composition of the magma. Text Reference: pages 61-75

  4. Igneous Magma Compositions: • Mainly silicate minerals. • Determined by composition of magma from which it crystallized. • Magma has mainly 8 elements: • Si, O, Al, Ca, Na, K, Mg, Fe • *Most abundant constituents

  5. . . Ca-Rich Plagioclase Mafic Intermediate Na-Rich Plagioclase Felsic Igneous Magma Compositions: • The minerals that are present in any igneous rock depends on the chemical composition and the environment (temperature of the magma) from which the molten rock crystallizes. • N. L. Bowen discovered that different minerals form at different temp.. • Bowen also noted that minerals will react with the magma to produce the next mineral in the reaction series, this is known as Bowen’s Reaction Series.

  6. Ca-Rich Plagioclase Mafic Intermediate Na-Rich Plagioclase Felsic Igneous Magma Compositions: • Olivine and Ca-rich plagioclase feldspar are the first to crystallize at very high temperatures and these minerals are often found in mafic igneous rocks. • Orthoclase feldspar and quartz crystallize at lower temperatures and are found in felsic igneous rocks • Therefore, igneous rocks are classified according to their mineral makeup as Mafic, Intermediate, or Felsic.

  7. Igneous Magma Compositions: • Magma • cools • solidifies • forms silicate minerals • Two major silicate mineral groups: • DARK Silicates • LIGHT Silicates

  8. Igneous Magma Compositions:

  9. Igneous Magma Compositions:

  10. Igneous Magma Compositions: • 3 main compositions: • “Mafic” :magnesium + ferrum • :high in Mg, Fe. Dark, dense • Basaltic • Andesitic • Granitic • “Felsic” :feldspar + silicate • :high in Si, lighter, less dense • “Intermediate”

  11. Mafic Magma Composition: • contain magnesium and iron rich minerals • form at high temperatures 1200EC • found mainly in oceanic crust • form most volcanic rocks (Basalt) • low percentage of silica, very fluid magmas • forms dark colored minerals, thus rocks are dark color • minerals include; olivine, pyroxene, plagioclase feldspar

  12. Mafic Magma Composition: zooming in basalt volcanic m a f i c gabbro plutonic

  13. Intermediate Magma Composition: • contains 25% dark silicate minerals (Amphibole, Pyroxene,andBiotite Mica) • forms at moderate temperatures, approximately 800EC • found associated with volcanic activity confined to the margins of the continents • form mainly volcanic intermediate rocks (Andesite) • high percentage of silica, very viscous (thick) magmas • contains both light and dark colored minerals • minerals include; Amphibole, Pyroxene, Biotite Mica and Plagioclase Feldspar

  14. Intermediate Magma Composition: zooming in andesite volcanic i n t e r m e d i a t e plutonic diorite

  15. Felsic Magma Composition: • contains orthoclase feldspar and quartz (silica) • forms at lower temperatures, approximately 600EC • found mainly in continental crust • form mainly plutonic rocks (Granite) • high percentage of silica, very viscous (thick) magmas • forms light colored minerals, thus rocks are light colored • minerals include; orthoclase and plagioclase feldspars, . quartz, and muscovite mica

  16. granite rhyolite Felsic Magma Composition: zooming in volcanic f e l s i c plutonic

  17. Felsic Magma Composition: obsidian volcanic f e l s i c pumice volcanic

  18. Mineral Composition: Classification Chart

  19. Mineral Composition:

  20. Example 1: What is the correct match for magma composition and environment?

  21. Example 2: Which pair of rocks have the same mineral composition?(A) andesite and granite (B) andesite and rhyolite (C) basalt and diorite (D) basalt and gabbro

  22. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Explain how mineral composition could be used to classify igneous rocks.

  23. Solutions . . . Question: Explain how mineral composition could be used to classify igneous rocks. Mineral Composition: If the igneous rock is light color and consist of the minerals quartz and orthoclase feldspar, it is classified as felsic. If the igneous rock is dark color and consist of the minerals pyroxene and plagioclase feldspar, it is classified as mafic.

  24. Summary . . . Overview of Points covered: • Bowen’s reaction series.

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