Rocks: Igneous Rocks

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Rocks: Igneous Rocks

  1. 1. Rocks September 14, 2011
  2. 2. Major Types of Rocks <ul><li>A rock is a group of minerals bound together. </li></ul><ul><li>The three types of rocks are igneous, sedimentary, and metamorphic. </li></ul>
  3. 3. Major Types of Rocks <ul><li>Igneous </li></ul><ul><ul><li>Formed from a melt (molten rock) </li></ul></ul><ul><ul><li>Plutonic (INTRUSIVE): slow cooling and large crystals </li></ul></ul><ul><ul><li>Volcanic (EXTRUSIVE, EXTRUSION): rapid cooling at the surface </li></ul></ul>
  4. 4. Major Types of Rocks <ul><li>Sedimentary </li></ul><ul><ul><li>Formed at the Earth’s surface </li></ul></ul><ul><ul><li>CLASTIC (Mineral fragments or grains, clays) </li></ul></ul><ul><ul><li>CHEMICAL (crystalline chemical/biochemical precipitates) </li></ul></ul>
  5. 5. Clastic sedimentary rocks
  6. 6. Chemical sedimentary rocks
  7. 7. Major Types of Rocks <ul><li>Metamorphic </li></ul><ul><ul><li>Changed by heat, pressure, and fluids </li></ul></ul>
  8. 8. The Rock Cycle <ul><li>Mark out the guide on your notes and draw your own, from the book, on a sheet of paper . The rock cycle can be found on page 67 in your books. </li></ul><ul><li>Include the 5 main parts and label, including the events that lead to the next stage in the cycle. </li></ul><ul><li>I will come around to staple your drawing to your notes. </li></ul>
  9. 9. The Rock Cycle On page 67 in your books
  10. 10. In conclusion… <ul><li>The rock cycle demonstrates the relationships among the THREE major rock groups </li></ul><ul><li>It is powered by the INTERNAL HEAT of the Earth as well as Earth’s momentum and the energy from the SUN </li></ul><ul><li>It involves processes on the Earth’s surface as well as the Earth’s interior </li></ul><ul><li>It connects the “hydrologic cycle” with the “tectonic cycle” </li></ul>
  11. 11. Igneous Rocks
  12. 12. Igneous Rocks <ul><li>Igneous rocks form when magma cools and hardens. </li></ul>Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL Igneous from the Latin meaning “Fire formed”, is a rock type that forms from the solidification of a molten mineral solution.
  13. 13. All igneous rocks have a random fabric of fused mineral grains.
  14. 14. Igneous Rocks <ul><li>Intrusive (Plutonic) rocks form inside the Earth (underground) when magma cools slowly to create large crystals. </li></ul><ul><ul><ul><li>( In trusive = In side) </li></ul></ul></ul><ul><li>Extrusive (Volcanic) rocks form on the Earth’s surface (above ground) when lava cools quickly to create small crystals. </li></ul><ul><ul><ul><li>( Ex trusive = Ex it/outside) </li></ul></ul></ul>
  15. 15. Intrusive: Large crystals <ul><li>Extrusive: Small crystals </li></ul>Which is which? How do you know?
  16. 16. Igneous Rocks <ul><li>There are two types of magma </li></ul><ul><ul><li>Felsic = Light color , high in silica, viscous (thick and slow), low in iron, calcium or magnesium </li></ul></ul><ul><ul><li>Felsic = Fel dspar + Si lica </li></ul></ul><ul><ul><li>Mafic = Dark color , low in silica, not viscous (thin and watery), high in iron, calcium and magnesium </li></ul></ul><ul><ul><li>Mafic = Ma gnesium + Iron ( F e) </li></ul></ul>
  17. 17. Felsic: Light overall color <ul><li>Mafic: Dark overall color </li></ul>Which is which? How do you know?
  18. 18. Igneous Rocks <ul><li>Texture refers to the crystal size. </li></ul><ul><li>Textures are divided into two main types: </li></ul><ul><ul><li>Fine-grained = crystals are too small to see (basalt) </li></ul></ul><ul><ul><li>Coarse-grained = crystals are easily visible (granite) </li></ul></ul>
  19. 19. Coarse Grained: Large crystals <ul><li>Fine Grained: Small crystals </li></ul>Which is which? How do you know?
  20. 20. Igneous Rocks <ul><li>Other types of textures: </li></ul><ul><li>A glassy texture occurs when rock freezes instantly. There are no crystals (obsidian). </li></ul><ul><li>A porphyritic texture is a rock with large crystals surrounded by fine-grained crystals (ryolite). </li></ul><ul><li>A vesicular texture is a rock that has many holes in it (pumice). </li></ul>
  21. 21. Volcanic Glass/Obsidian : may be felsic, but is usually mafic. Even when felsic it appears dark nonetheless because the small % of mafic minerals in the rock form a homogenous solution with the felsic minerals tinting the overall color to dark. Notice the conchoidal fracture. Glassy Texture:
  22. 22. Porphyritic Texture: <ul><li>Rhyolite : Light colored (felsic), fine grained (volcanic) igneous rock </li></ul>
  23. 23. Pumice : Fine grained, felsic, vesicular volcanic igneous rock. <ul><li>Scoria : Fine grained, mafic, vesicular volcanic igneous rock. </li></ul>Vesicular Texture :
  24. 24. Igneous Rocks <ul><li>Rocks can be grouped into families: </li></ul><ul><li>Granite family = felsic, light, contains quartz, feldspar, & muscovite. </li></ul><ul><ul><li>(granite, rhyolite, obsidian, pumice) </li></ul></ul><ul><li>Gabbro family = mafic, dark, contains feldspar, olivine, biotite. </li></ul><ul><ul><li>(gabbro, basalt, scoria) </li></ul></ul><ul><li>Diorite family = intermediate composition and color. </li></ul><ul><ul><li>(diorite, andesite, obsidian) </li></ul></ul>
  25. 25. Igneous Rocks <ul><li>Let’s try some examples, tell me if the following rock samples are: </li></ul><ul><li>1. Felsic or Mafic </li></ul><ul><li>2. Fine grained or Coarse grained </li></ul><ul><li>3. Intrusive or Extrusive </li></ul><ul><li>Be sure to tell me how you knew. </li></ul>
  26. 26. Basalt Mafic = Dark color Fine grained = Small crystals Extrusive = Small crystals = Formed on surface
  27. 27. Diorite Felsic = Light color Coarse grained = Large crystals Intrusive = Large crystals = Formed underground
  28. 28. Gabbro Mafic = Dark color Coarse grained = Large crystals Intrusive = Large crystals = formed underground
  29. 29. Pumice Felsic = Light color Fine grained = Small crystals Extrusive = Small crystals = Formed above ground
  30. 30. Scoria Mafic = Dark color Fine grained = Small crystals Extrusive = Small crystals = Formed above ground
  31. 32. Remember: Safety First!!! Intermission

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