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IgneousIgneousRocks
http://www.soest.hawaii.edu/coasts/lecture/gg101/index.html
What is Igneous Rock?
Earth’s crust is 4/5 igneous rock.Every igneous rock begins life as molten magma deep in the mantle.As magma migrates toward the surface, some of it chills and hardensunderground into granite and other types of igneous rocksunderground into granite and other types of igneous rocks.Magma that makes it to the surface erupts in either flowing orexplosive volcanoes, generating lava, geysers, and hot springs.
Igneous rock crystallizes in Earth’s magma locations Intrusive
igneous rock crystallizes
within
Earth’s crust.
Extrusive
igneous rock crystallizes
upon
Earth’s crust.
Extrusive igneous rock
Intrusive igneous rock
Igneous Rocks
• Igneous Rocks are named on the basis of
th i
t
t
d
iti
their texture and composition.
Composition
of a rock is the
assemblage
of minerals it contains.
Texture
of a rock is the
size and arrangement
of the minerals it contains.
As magma crystallizesa network of interlockingminerals develops.The
composition
and
texture
of the resulting
rock is determined by
y
these minerals.
Phaneritic texture
with large minerals(Granite)
Texture
(Granite)
Large crystals had a long time to crystallize.Therefore, this is an intrusive rock
Aphanitic texture
small to see with the unaidedeye (Basalt)
Texture
Small crystals had a short time to crystallize.Therefore, this is an extrusive rock
Remember, partial melting produces magma that is enriched inSilicon and Oxygen and depleted in Iron and Magnesium
Felsic
oxygen, silicon, sodium enriched
iron, magnesium, calcium depleted
Source
- partial melting, continental crust
Granite -pink is considered felsic
Composition
Intermediate Mafic
iron, magnesium, calcium enriched
oxygen, silicon, sodium depleted
S
Diorite
Basalt
Source
Ultramafic
Dunite
Composition Remember partial melting?Silica (felsic) compounds melt first – therefore in a cooling magma chamberthey must crystallize last
How do igneous rocks form in a cooling magma chamber?
Iron-rich (mafic) compounds melt last – therefore in a cooling magma chamberthey must crystallize first
Melting
last
Mafic – Fe/Mg/Ca
Crystallizing
first
Mafic – Fe/Mg/Ca
Melting
first
Felsic – Si/O/Na
Crystallizing
last
Felsic – Si/O/Na
Therefore a cooling magma chamber will become enriched in Si/O as it crystallizes
Olivine Pyroxene
Igneous Rock-Forming
Minerals
Orthoclase
PlagioclaseFeldspar(Ca/Na)
Amphibole
MaficMinerals
FeldsparFelsicMinerals
MuscoviteMi
BiotiteMica
Mica
Quartz
How do igneous rocks form?
Bowen’s Reaction Series
Mafic
Hot
Olivine
Ca - plagioclase
Ultramafic
BasaltGabbro
Types ofRocks formed
Mafic
Pyroxene
Amphibole
Biotite
Orthoclase
Na - plagioclase
Plagioclase
feldspar
Intermediate
Felsic
AndesiteDiorite
Cool
feldspar
Muscovite
Quartz
RhyoliteGranite
The IgneousMinerals
Intrusive Extrusive
Granite Rhyolite
Andesite
Basalt
Diorite
Gabbro
Texture
The IgneousRocks
volcanic plutonic
Felsic
Intermediate
Mafic
Composition
Where do the Igneous
Rocks form?
Granite
Diorite
Gabbro
Rhyolite
Andesite
Basalt
IntrusiveExtrusive
Felsic
Intermediate
Mafic
