Igneous Rocks

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Igneous Rocks
Mt. Rushmore
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Half Dome, Yosemite, CA Ansel Adams
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IGNEOUS ROCKS Some igneous rocks form from cooled
lava that has exited Earths crust
Hawaii
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Some Igneous rocks cool from magma inside Earth
and later become exposed through pressure,
uplift, and erosion!!!
Half Dome, Yosemite, California
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Igneous

• Think of ignite
• To light a fire
• Igneous rock comes from the heat within Earth
  Geothermal

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How are Igneous Rocks Classified?

• Igneous rocks are classified by
• 1. Mineral Composition
• 2. Crystal Size (Texture)

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Igneous Rock Formation

• ?Most Igneous rocks form directly from Magma
  which is hot, molten rock
• Granite is the most common igneous rock, it
  cooled from magma
• Igneous rocks can also form from lava

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3. First Classification of Magma

• Felsic
• Is rich in Silica (SiO2)
• Small amounts of Ca, Fe, Mg (Calcium, Iron,
  Magnesium)
• Slow-moving, thick HIGH VISCOSITY (resistance to
  flowing)
• Crystallizes to light-colored minerals
• Resulting rocks have relatively low density
• Felsic rocks make up the continents

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Examples of FELSIC igneous rocks
Pumice
Rhyolite
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4. Second Classification of Magma

• Mafic
• Low amounts of Silica (SiO2)
• Fe and Mg rich (Iron and Magnesium)
• Fast-moving, thinner LOW Viscosity less
  resistance to flowing, more fluid
• Crystallize to dark-colored minerals
• Resulting rocks have relatively high density
• Mafic rocks make up the ocean floors

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Mafic Igneous Rock examples
Basalt (ocean floor)
Gabbro
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5. Crystal Size

• It takes time to grow crystals
• As magma cools, it crystallizes
• If magma cools slowly, what size crystals will
  form?

Large Crystals
If Magma cools quickly, small crystals will form
because they have little time to grow.
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Igneous Rock
Obsidian cools so fast that no crystals have time
to form A.K.A. Volcanic glass
Obsidian is dark in color due to iron oxides.
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6. Igneous Rocks
Granite

• ?Intrusive
• Igneous rock that crystallizes below Earths
  surface, from magma
• Intrusive Inside Earth

Large Crystal size
Notice how Granite has large crystals, it cooled
slowly from magma deep beneath Earths surface
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Igneous Rocks

• ?Extrusive
• Igneous rock that crystallizes or forms at
  Earths surface, from lava
• Extrusive exited Earth

Basalt
Small Crystal size
Notice how basalt has small crystals, it cooled
quickly at Earths surface
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Lava is magma that has reached the Earths
surface.
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Igneous Rocks

• ?EXT-rusive
• EXITED Earth
• ?IN-trusive
• Formed IN-side Earth

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Crystal Size

• ?Intrusive Rock (Large Crystal Size)
• Because it is inside the Earth, it cools very
  slowly, giving crystals time to grow
• ?Extrusive Rock (Small crystal size)
• Cools very quickly so crystals do not have time
  to form

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Composition (what its made of) of Granite

• Granite Rock contains the following minerals
• Quartz
• Feldspar
• Mica

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Igneous Rock
Felsic (Light Color) Continents Mafic (Dark Color) Ocean Floor
Intrusive Cools slowly From Magma Large crystals (SiO2) rich Large crystals Fe, Mg rich
Extrusive Cools quickly From Lava Small or no crystals (SiO2) rich Small or no crystals Fe, Mg rich
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Igneous Rock
Felsic (Light Color) Continents Mafic (Dark Color) Ocean Floor
Intrusive Cools slowly From Magma Large crystals (SiO2) rich Large crystals Fe, Mg rich
Extrusive Cools quickly From Lava Small or no crystals (SiO2) rich Small or no crystals Fe, Mg rich
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Igneous Rock
Felsic (Light Color) Continents Mafic (Dark Color) Ocean Floor
Intrusive Cools slowly From Magma Large crystals (SiO2) rich Large crystals Fe, Mg rich
Extrusive Cools quickly From Lava Small or no crystals (SiO2) rich Small or no crystals Fe, Mg rich
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Igneous Rock
Felsic (Light Color) Continents Mafic (Dark Color) Ocean Floor
Intrusive Cools slowly From Magma Large crystals (SiO2) rich Large crystals Fe, Mg rich
Extrusive Cools quickly From Lava Small or no crystals (SiO2) rich Small or no crystals Fe, Mg rich
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Igneous Rock
Felsic (Light Color) Continents Mafic (Dark Color) Ocean Floor
Intrusive Cools slowly From Magma Large crystals (SiO2) rich Large crystals Fe, Mg rich
Extrusive Cools quickly From Lava Small or no crystals (SiO2) rich Small or no crystals Fe, Mg rich
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Igneous Rock
Felsic (Light Color) Continents Mafic (Dark Color) Ocean Floor
Intrusive Cools slowly From Magma Large crystals (SiO2) rich Large crystals Fe, Mg rich
Extrusive Cools quickly From Lava Small or no crystals (SiO2) rich Small or no crystals Fe, Mg rich
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IGNEOUS

• FELSIC
• Light colored
• Less dense
• Rich in silica (SiO2)
• Magma flows slowly, thick
• Continental crust

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IGNEOUS

• MAFIC
• Dark colored
• Very dense
• Rich in iron (Fe) and magnesium (Mg)
• Magma flows quickly, thin
• Oceanic crust

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IGNEOUS

• EXTRUSIVE
• exit
• Magma exits the Earth before cooling
• Cools and crystalizes quickly
• Small or no crystals

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IGNEOUS

• INTRUSIVE
• in
• Magma cools inside the Earth
• Cools and crystalizes slowly
• Large crystals

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Igneous Rock Lab

• Use your Igneous observations sheet
• Rotate independently between the 25 stations set
  up around the room
• Start with whichever station number you are
  located
• Round 1 You will have less than 1 minute at each
  station
• Do not switch to the next station until told to
  do so, only 1 person at at station (if you have
  extra time, study your notes)
• Round 2 You may go back to any unoccupied
  station, if needed