Chapter 3 section 2 igneous rocks
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Chapter 3 Section 2 Igneous Rocks. From the core of the continents to nearly all of the oceanic crust—igneous is everywhere!. IGNEOUS ROCKS. magma lava. “fire” rocks. cooling. andesite. pumice. Formed from cooled/hardened _________ or ______

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Chapter 3 Section 2 Igneous Rocks

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Chapter 3 Section 2 Igneous Rocks

From the core of the continents to

nearly all of the oceanic crust—igneous is everywhere!


IGNEOUS ROCKS

magma lava

“fire” rocks

cooling

andesite

pumice

Formed from cooled/hardened _________ or ______

Are called _______________ [ignis Latinfire]

The rate of __________ determines the size of the mineral’s crystals.

basalt


INtrusive: below groundcools slower many many &large crystals

Ex: granite, gabbro


Intrusive Igneous

  • Visible due to erosion & weathering

  • Magma= mainly silicon & oxygen

    • Gases: water vapor (gases trapped)

  • Magma less dense than surrounding rock moves towards surface & cools

    • Elements combine minerals form & ‘grow’ crystals!

      • Example:

        • Granite

        • Cumberlandite


Intrusive Igneous: Cumberlandite

  • Only found in Cumberland, RI (official state rock)

    • 4-acre lot in Blackstone Valley (Iron Mine Hill) & trace amts. Narr. Bay

  • Dense & prone to rust (iron  magnetic); titanium, transitions to peridotite (intr. coarse ign.)

  • Formed 1.5 bya  volcanic activity

  • Valuable  cannon and farm tools 18th/19th cent.


Obsidian

EXtrusive: above groundcools quicker f e w &small crystals

Air bubbles are sometimes trapped (pumice, scoria)

Basalt


Extrusive Igneous

Basalt

  • Magma = below ground// Lava= above ground

    • Lava most gases escaped

  • Lava hardens extrusive igneous rock

    • Extruded onto surface

    • Example: Rhyolite, Basalt


Classifying Igneous Rocks

  • Classification based on two major characteristics:

    • Texture: appearance based on size, shape & arrangement of crystals

    • Composition: proportions of light and dark minerals


Classification: Texture

  • Coarse-grained: slow cooling large crystals

    • Allows charged atoms (ions) to move large distances within magma & link together (crystallize)

  • Fine-grained: rapidcooling  small crystals

    • Ions lose motion and quickly combine; all compete for available ions

  • Glassy: lava on surface little time for ions to

    crystallize randomly distributed 

    glassy appearance (tiny crystals)

  • Porphyritic: different-sized minerals experience

    different rates of cooling

    • Large crystals (phenocrysts) may be surrounded by

      fine grained minerals

    • Minerals don’t crystallize @ same rate (location and

      melting point.)


  • Classification: Composition

    • Granitic: light-colored silicates (quartz & feldspar)

      • 70 % silica

      • 10 % dark silicate minerals (i.e. biotite mica, amphibole)

      • Major component of continental crust

      • Ex: rhyolite = extrusive granitic rock

    • Basaltic: contain many dark silicate materials (plagioclase feldspar)

      • Rich in magnesium and iron

        • Iron  darker and denser than granitic rocks

      • Ex: gabbro = intrusive basaltic rock

    • Andesitic: composition between granitic and basaltic

      • Volcanic rock = andesite:

        • At least 25 % dark silicates (amphibole, pyroxene, biotitemica)

        • Dominant mineral plagioclase feldspar :type of feldspar dark w/ridges (striations)

    • Ultramafic: composed almost entirely of dark silicate minerals

      • Rare @ Earth’s surface

        • Ex: peridotite—upper mantle composition


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