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5.1 Igneous Rocks
 

5.1 Igneous Rocks

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5.1 Igneous Rocks 5.1 Igneous Rocks Presentation Transcript

  • Igneous Rocks Pages 99 - 113
  • Goal 1 Compare and contrast intrusive and extrusive igneous rocks
  • All rocks are a mixture of minerals. Mineral soup
    • Each type of rock has its own mix of minerals
    Gabbro: minerals include hornblende, plagioclase, pyroxene, biotite, olivine, magnetite
    • Extrusive Igneous Rocks
    • 1. Lava cooled quickly at surface
  •  
  • Kalapana, Hawaii 1990
  • Lava fountain height approx 10 m Pu‘u Kahaualea , photo by J.D. Griggs, 02/25/83 USGS
    • 2. Fine grain / glassy
    • 3. Examples
    Obsidian Pumice
    • Intrusive Igneous
    • Rocks
    • 1. Cooled magma inside Earth
    • 2. Cross cutting relationships
    Photo credit: Eurico Zimbres
  • Photo credit: Wing-chi Poon at Devil's Lookout Point, Black Canyon Gunnison National Park, Colorado, USA
    • 3. Coarse Grain
    • +large, interlocking crystals
    • +naked eye
    • 4. Examples
  • Granite porphyry: coarse grains surrounded by fine grains
  • Goal 3 Explain the 4 factors that affect how rocks melt and crystallize
    • Magma forms in the Earth’s Mantle
    • Slushy mix
    • Solids
    • Liquids
    • Gases
    • Temperature
      • Temp increases w/ depth
    • 2. Pressure
    • a) pressure increases with depth
    • b) increased pressure = higher melting temp
    • 3. Water content
    • a) water increase = melting point decrease
    • 4. Mineral composition
    • a) minerals have individual unique melting points
    • Bowen’s Reaction series
    • Explains the order in which minerals crystallize out of a magma solution
    • Bowen’s Reaction Series
    Image Credit: James Madison University Geology Dept.
    • Left side
    • Iron-rich minerals
    • Discontinous
    • crystallization
    Right side Feldspar minerals Continuous crystallization
  • SiO 2 content is related to classification Dark / Green Ultramafic 0% Dark Mafic < 50% Basaltic ½ light ½ dark Intermediate ~ 60% Andesitic Light Felsic > 70% Rhyolitic General color Classification SiO 2 content Magma type
    • Summary
    • Texture related to location of crystallization
      • Fine grain = extrusive
      • Coarse grain = intrusive
      • Porphyritic = intrusive
    • Mineral content related to crystallization series
      • Fe rich = discontinuous
      • Na, Ca Feldspars = continuous
    • Classification related to SiO 2 content and color
      • Light = Felsic
      • ½ and ½ = Intermediate
      • Dark = Mafic
      • Very dark / green = Ultramafic
  • Determining if a rock is Igneous:
    • Hard, scratches glass
    • No banding or layers of colors
    • Coarse-grain (large crystals) that interlock
    • Fine-grain (small crystals), glassy, light / holey from gas pockets
    • Common colors: black, white, gray, reds to pinks
    • Thanks to the following people who have generously shared photos on the creative commons at Flickr:
    • The Shifted Librarian… Road Closed
    • James_C… Red granite Cross
    • Kevinzim… gabbro slice
    • Jeff gerhard… lava
    • AZAdam… lava tube
    • Travis S… obsidian point
    • Ambuj Saxena… pumice
    • Kevinzim… coarse grain intrusive
    • Basial… Intrusive examples