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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 3.4. Igneous Classification Chart. Focus on . . . identifying the eight rock forming minerals.

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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 3.4 Igneous Classification Chart Focus on . . . • identifying the eight rock forming minerals. • describing the mineralogy associated with common igneous rocks and relate to igneous compositions and textures.

  3. Rock Forming Minerals • All Igneous rocks originally solidified from magma/lava. • Igneous rocks form from Eight minerals called therock forming minerals. 1) Olivine 5) Plagioclase Feldspar 2) Pyroxene 6) Orthoclase Feldspar 3) Amphibole 7) Muscovite Mica 4) Biotite Mica 8) Quartz

  4. Igneous Rocks • Type of Igneous rock formed depends on the environment where it crystallizes. • Two main environments: • Volcanic • Molten rock cools on or near Earth’s surface which results in very small crystals. • Plutonic • Molten rock cools beneath Earth’s surface which results in larger more uniform sized crystals. Text Reference: Pages 61-73

  5. Rocks become darker in color Volcanic Igneous Rocks Rhyolite: • Quartz and Orthoclase feldspar • Light in color ( < 15% dark minerals) • Microscopic crystals (fine texture)

  6. Rocks become darker in color Volcanic Igneous Rocks Andesite: • Amphibole and Plagioclase feldspar • Medium colored ( < 40% dark Minerals) • Microscopic crystals (fine texture)

  7. Rocks become darker in color Volcanic Igneous Rocks Basalt: • Pyroxene and Plagioclase feldspar • Dark in color ( > 40% dark minerals) • Microscopic crystals (fine texture)

  8. Rocks become darker in color Plutonic Igneous Rocks Gabbro: • Pyroxene and Plagioclase feldspar • Dark in color ( > 40% dark minerals) • Visible crystals (coarse texture)

  9. Rocks become darker in color Plutonic Igneous Rocks Diorite: • Amphibole and Plagioclase feldspar • Medium colored ( < 40% dark Minerals) • Visible crystals (coarse texture)

  10. Rocks become darker in color Plutonic Igneous Rocks Granite: • Quartz and Orthoclase feldspar • Light in color ( < 15% dark minerals) • Visible crystals (coarse texture)

  11. Classification of Igneous Rocks A general classification scheme based on chemical composition and texture is provided in the following diagram.

  12. Classification of Igneous Rocks • Overview of topics: • Rock Forming Minerals: • Composition; • Felsic • Intermediate • Mafic • Environment (Texture); • Intrusive (Plutonic) • Extrusive (Volcanic)

  13. Classification of Igneous Rocks Questions: What minerals would be found in an average composition of Granite? Basalt?

  14. Classification of Igneous Rocks Questions: 2) What minerals would be found in most all igneous rocks?

  15. Classification of Igneous Rocks Questions: 3) What minerals would you never find in;i) Felsic igneous rocks?ii) Mafic igneous rocks?

  16. Example 1: Using the diagram below, answer the following questions: • What is the volcanic equivalent of a rock that has 55% plagioclase feldspar, 25% hornblende and 20% pyroxene? • (A) andesite (B) basalt • (C) komatiite (D) rhyolite • Based on the diagram, which mineral is found in most igneous rocks? • plagioclase feldspar (B) biotite(C) potassium feldspar (D) olivine

  17. Example 2: What characteristic allows two igneous rocks with the same mineral composition to have different names? (A) colour (B) foliation (C) shape (D) texture Which intrusive/extrusive pair of rocks have the same mineral composition? basalt/andesite (B) gabbro/basalt (C) granite/diorite (D) granite/andesite

  18. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Explain why two igneous rocks can have the same mineral composition, but have different rock names.

  19. Solutions . . . Answer: The type of Igneous rock not only depends on its mineral composition, but also, on the environment in which the molten rock crystallized. The environment will determine the texture of the rock, which is another factor used to classify (Name) igneous rocks. Thus, two igneous rocks with the same mineral composition and have different textures, will have different names. For Example;Rhyolite and Granite (Felsic composition)Andesite and Diorite (Intermediate composition)Basalt and Gabbro (Mafic composition)

  20. Summary . . . Overview of Points covered:

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