Download Chapter 5 - Igneous Rocks

Igneous Rocks
What is an Igneous Rock?
 Igneous rocks are rocks
formed when molten rock
cools and solidifies.
There are two terms used for
molten rock.
MAGMA
 Molten rock inside
the Earth is called
magma.
 Once formed,
magma rises
toward the surface
because it is less
dense than the
surrounding rocks.
LAVA
 Lava is the word
for magma when it
erupts onto the
Earth's surface.
2 Types of Igneous Rocks
 Intrusive Igneous
Rocks:
 Form beneath
Earth’s surface
 Cool slowly
 Large crystals
2 Types of Igneous Rocks
 Extrusive Igneous
Rocks:
 Form on Earth’s
surface
 Cool quickly
 Small crystals
 Sometimes no
crystals
Classification is based on
crystal size and composition.
Crystallization
 The formation and growth of a
crystalline solid from a liquid or gas.
 Remember the crystal shapes we
discussed for properties of
minerals.
Types of Igneous Textures
1.
2.
3.
4.
5.
6.
Aphanitic
Phaneritic
Porphyritic
Glassy
Pyroclastic
Pegmatitic
Aphanitic/Phaneritic
 Aphanitic




Rapid cooling
Small crystals
Fine –grained texture
Extrusive rock
 Phaneritic
 Slow cooling
 Large crystals
 Coarse-grained
texture
 Intrusive rock
Porphyritic/Glassy
 Porphyritic
 Contains large and
small crystals in one
rock.
 Due to certain
minerals crystallizing
quicker than others.
 Glassy




Rapid cooling
No crystals
Looks like glass
Extrusive rock
Pyroclastic/Pegmatitic
 Pyroclastic
 Clumps of rock
fragments
 Form from volcanic
rock
 Pegmatitic
 Exceptionally coarsegrained texture
 Formed from a fluidrich environment
 Crystals all larger
than 1cm
Igneous Compositions:
Granitic composition
Basaltic composition
 Composed of light
colored silicates.
 Composed of dark
colored silicates.
 Ex. quartz and feldspar
 Ex. ferromagnesian
minerals
-Make up the continental crust
-Make up the oceanic crust