Igneous Rocks

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Igneous Rocks

• Make up 95 of earths crust
• Most common are on the continents - Andesite and
  Granite
• Most common on the ocean floor basalt
• All Igneous rocks originate as magma or molten
  rock from the earths interior

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Igneous Rocks

• Rocks start melting at 750 C
• Temp increases about 30 C each km toward the
  center of the earth

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Igneous Rocks
Melting depends on pressure water content
Higher pressure higher melting point
More water lower melting point Rocks with
lower melting point will melt first and solidify
(crystallize) first when cooled
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• Magma is classified by the amount of silica
  (SiO2) that it contains
• Basaltic 50 silica
• Andesitic 60 silica
• Granite 70 silica

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Igneous Rocks

• Extrusive Rocks that form at the earths surface
  (lava)
• Intrusive Rocks that form beneath the earths
  surface

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Extrusive

• Lava molten material from the earth and the
  rocks that form from it
• Fissure outpouring of basaltic lava on the
  ocean floor
• Volcano outpouring of lava through a vent

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Fissure
Flood Basalts produced the Colombia Plateau
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• Volcano outpouring of lava through a vent
• Shield volcano broad gentile slopes
• Cinder cone smooth steep slopes and a bowl
  shaped summit
• Composite cones steep sided summit gradual
  slopes

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Volcano
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Formations Under Ground

• Igneous rock formations intrusive rock
• Plutons large intrusive rock body beneath the
  earths surface

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Plutons
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Plutons

• Dike formed by the intrusion of magma into
  fractures that cut across the layers of
  existing rock
• Shiprock New Mexico

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Plutons

• Sill intrusion of magma into fractures that are
  parallel to the layering
• Laccolith mushroom shaped sill that pushes the
  rock layers upward

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Plutons

• Batholiths large sill or laccolith having a
  surface area greater than 100 square kilometers
  usually due to a number of intrusive events

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Batholiths
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Plutons