physical science igneous rocks cont

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  1. Glassy texture
    - rapid cooling

    -most common rock : Obsidian

    Cools too fast to form crystals, Ions freeze unorderly
  2. Magma composition
    - Main elements: Oxygen and Silicon

    -Secondary elements: Al, Ca, Na, K, Mg, Fe

    -Minor elements: Ti, Mn

    -Trace elements: U, Au, Ag, not present in large quantities.
  3. 2 major groups of Igneous rocks
    Dark Silicates and Light Silicates
  4. Dark Silicates
    • rich in Fe and/or Mg, low Si
    • ex) Olivine, pyrosene, amphibole, and Biotite Mica
  5. Light silicates
    High in Si, no Fe or Mg

    greater amounts of K, Na, Ca- feldspars
  6. Granite composition (Felsic)
    -light colored silcates

    -high amounts of silica

    -major constitutent of continental crust

    -termed felsic (Feldspar and Silica)
  7. Basaltic composition
    - dark silicates and calcium rich feldspar

    -termed mafic (magnesium and ferrum (Fe))

    -higher density than granite rocks

    -comprise the ocean floor and many volcanic islands
  8. intermediate composition
    ex) Dionite

    -contains 25% or more dark silicate minerals

    -associated with explosive volcanic activity
  9. Ultramafic compostion
    -Rare, high in Mg and Fe

    -Compound entriely of ferromagnesion silicates

    -need a large volcanic event to pull them up from the ground
  10. Silica content and composition
    Si content in crystal rocks range from 45% to 70%

    -low end, Fe and Mg rich

    -high end, K, Na, and Ca rich
  11. Granite magmas
    very viscous, not much explosions once it settles in
  12. Besaltic magmas
    High Fe, less Si content

    less viscous. but once it settles causes extreme explosions
  13. Origin of magma
    -Originates from melting in Earth's upper mantle

    • -plate tectonics play major role
    • -divergent zones- greatest quantities

    some magmas originate deep within the mantle
  14. 3 Sources of magma that produces igneous activity


    -volatiles - water vapor, carbon dioxide
  15. *Role of heat
    • -geothermal gradient
    • -rate at which temp. increases with depth
  16. *Role of pressure
    pressure increases with depth

    - Increase confining, increase melting temperature of rock

    -less pressure, reduces melting temperature of a rock
  17. Role of volatiles
    • volatiles can cause rock to melt at lower temps
    • -effects magnified w/ increasing pressure

    "wet" rock at depth melts at lower temps than "dry" rock.
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physical science igneous rocks cont
2011-09-30 05:25:41

igneous rocks
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