Igneous RocksIgneous 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.

LAVALAVA Lava is the word Lava is the word

for for magma when it erupts onto the Earth's surface.

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