Igneous Rocks Igneous Rocks
What is an Igneous Rock?What is an Igneous Rock?
Igneous rocks are rocks Igneous rocks are rocks formed when molten rock formed when molten rock cools and solidifies.cools and solidifies.There are two terms used for There are two terms used for
molten rock.molten rock.
MAGMAMAGMA Molten rock inside Molten rock inside
the Earth is called the Earth is called magma.magma.
Once formed, Once formed, magma rises magma rises toward the surface toward the surface because it is less because it is less dense than the dense than the surrounding rocks.surrounding rocks.
2 Types of Igneous Rocks2 Types of Igneous Rocks
Intrusive Igneous Intrusive Igneous Rocks:Rocks:
Form beneath Form beneath Earth’s surfaceEarth’s surface
Cool slowlyCool slowly Large crystalsLarge crystals
2 Types of Igneous Rocks2 Types of Igneous Rocks
Extrusive Igneous Extrusive Igneous Rocks:Rocks: Form on Earth’s Form on Earth’s
surfacesurface Cool quicklyCool quickly Small crystals Small crystals
Sometimes no Sometimes no crystalscrystals
Classification is based on Classification is based on crystal size and crystal size and composition.composition.
CrystallizationCrystallization
The formation and growth of a The formation and growth of a crystalline solid from a liquid or gas.crystalline solid from a liquid or gas.
Remember the crystal shapes we Remember the crystal shapes we discussed for properties of discussed for properties of minerals.minerals.
Types of Igneous Types of Igneous TexturesTextures
1.1. AphaniticAphanitic
2.2. PhaneriticPhaneritic
3.3. PorphyriticPorphyritic
4.4. GlassyGlassy
5.5. PyroclasticPyroclastic
6.6. PegmatiticPegmatitic
Aphanitic/PhaneriticAphanitic/Phaneritic
AphaniticAphanitic Rapid coolingRapid cooling Small crystalsSmall crystals Fine –grained textureFine –grained texture Extrusive rockExtrusive rock
PhaneriticPhaneritic Slow coolingSlow cooling Large crystalsLarge crystals Coarse-grained Coarse-grained
texturetexture Intrusive rockIntrusive rock
Porphyritic/GlassyPorphyritic/Glassy
PorphyriticPorphyritic Contains large and Contains large and
small crystals in one small crystals in one rock.rock.
Due to certain Due to certain minerals crystallizing minerals crystallizing quicker than others.quicker than others.
GlassyGlassy Rapid coolingRapid cooling No crystalsNo crystals Looks like glassLooks like glass Extrusive rockExtrusive rock
Pyroclastic/PegmatiticPyroclastic/Pegmatitic
PyroclasticPyroclastic Clumps of rock Clumps of rock
fragmentsfragments Form from volcanic Form from volcanic
rockrock
PegmatiticPegmatitic Exceptionally coarse-Exceptionally coarse-
grained texturegrained texture Formed from a fluid-Formed from a fluid-
rich environmentrich environment Crystals all larger Crystals all larger
than 1cmthan 1cm
Igneous Compositions:Igneous Compositions:
Granitic compositionGranitic composition
Composed of light Composed of light colored silicates.colored silicates.
Ex. quartz and feldsparEx. quartz and feldspar
-Make up the continental -Make up the continental crustcrust
Basaltic compositionBasaltic composition
Composed of dark Composed of dark colored silicates.colored silicates. Ex. ferromagnesian Ex. ferromagnesian
mineralsminerals
-Make up the oceanic crust-Make up the oceanic crust