Transcript Igneous Rocks

Igneous Rocks
Mt. Rushmore
Half Dome,
Yosemite, CA
Ansel Adams
IGNEOUS ROCKS
Some igneous rocks form from cooled
lava that has exited Earth’s crust
Hawaii
Some Igneous rocks cool from
magma inside Earth and later
become exposed through
pressure, uplift, and erosion!!!
Half Dome,
Yosemite,
California
Igneous
 Think of “ignite”
To light a fire
 Igneous rock comes from the
heat within Earth: Geothermal
How are Igneous Rocks
Classified?
Igneous rocks are classified
by:
1. Mineral Composition
2. Crystal Size (Texture)
Igneous Rock Formation
Most Igneous rocks form directly
from Magma which is hot, molten
rock
 Granite is the most common
igneous rock, it cooled from magma
Igneous rocks can also form from lava
3. First Classification of Magma:
Felsic
 Is rich in Silica (SiO2)
 Small amounts of Ca, Fe, Mg (Calcium,
Iron, & Magnesium)
 Slow-moving, thick= HIGH VISCOSITY
(resistance to flowing)
 Crystallizes to light-colored minerals
 Resulting rocks have relatively low density
 Felsic rocks make up the continents
Examples of FELSIC
igneous rocks
Rhyolite
Pumice
4. Second Classification of Magma:
Mafic
 Low amounts of Silica (SiO2)
 Fe and Mg rich (Iron and Magnesium)
 Fast-moving, thinner= LOW Viscosity:
less resistance to flowing, more fluid
 Crystallize to dark-colored minerals
 Resulting rocks have relatively high
density
 Mafic rocks make up the ocean floors
Mafic Igneous Rock examples:
Basalt
(ocean floor)
Gabbro
5. Crystal Size
 It takes time to grow crystals
 As magma cools, it crystallizes
 If magma cools slowly, what size
crystals will form? Large Crystals
If Magma cools quickly, small crystals
will form because they have little time
to grow.
Igneous Rock
Obsidian cools
so fast that no
crystals have
time to form
A.K.A. Volcanic
glass
Obsidian is dark in color
due to iron oxides.
6. Igneous Rocks
Intrusive
 Igneous rock
that crystallizes
below Earth’s
surface, from
magma
 Intrusive=
Inside Earth
Granite
Large Crystal size
Notice how Granite has large crystals, it cooled
slowly from magma deep beneath Earth’s surface
Igneous Rocks
Extrusive
 Igneous rock
that crystallizes
or forms at
Earth’s surface,
from lava
 Extrusive=
exited Earth
Basalt
Small Crystal size
Notice how basalt has small crystals, it
cooled quickly at Earth’s surface
Lava is magma that has reached
the Earth’s surface.
Igneous Rocks
EXT-rusive
 EXITED
Earth
IN-trusive
 Formed
IN-side
Earth
Crystal Size
Intrusive Rock (Large Crystal Size)
 Because it is inside the Earth,
it cools very slowly, giving
crystals time to grow
Extrusive Rock (Small crystal size)
 Cools very quickly so crystals
do not have time to form
Composition (what it’s made of) of Granite
Granite Rock contains the
following minerals:
Quartz
Feldspar
Mica
Igneous Rock
Intrusive
Cools slowly
From Magma
Extrusive
Cools quickly
From Lava
Felsic
Mafic
(Light Color)
(Dark Color)
Continents
Ocean Floor
Large crystals
(SiO2) rich
Large crystals
Fe, Mg rich
Small or no
crystals
(SiO2) rich
Small or no
crystals
Fe, Mg rich
Igneous Rock
Intrusive
Cools slowly
From Magma
Extrusive
Cools quickly
From Lava
Felsic
Mafic
(Light Color)
(Dark Color)
Continents
Ocean Floor
Large crystals
(SiO2) rich
Large crystals
Fe, Mg rich
Small or no
crystals
(SiO2) rich
Small or no
crystals
Fe, Mg rich
Igneous Rock
Intrusive
Cools slowly
From Magma
Extrusive
Cools quickly
From Lava
Felsic
Mafic
(Light Color)
(Dark Color)
Continents
Ocean Floor
Large crystals
(SiO2) rich
Large crystals
Fe, Mg rich
Small or no
crystals
(SiO2) rich
Small or no
crystals
Fe, Mg rich
Igneous Rock
Intrusive
Cools slowly
From Magma
Extrusive
Cools quickly
From Lava
Felsic
Mafic
(Light Color)
(Dark Color)
Continents
Ocean Floor
Large crystals
(SiO2) rich
Large crystals
Fe, Mg rich
Small or no
crystals
(SiO2) rich
Small or no
crystals
Fe, Mg rich
Igneous Rock
Intrusive
Cools slowly
From Magma
Extrusive
Cools quickly
From Lava
Felsic
Mafic
(Light Color)
(Dark Color)
Continents
Ocean Floor
Large crystals
(SiO2) rich
Large crystals
Fe, Mg rich
Small or no
crystals
(SiO2) rich
Small or no
crystals
Fe, Mg rich
Igneous Rock
Intrusive
Cools slowly
From Magma
Extrusive
Cools quickly
From Lava
Felsic
Mafic
(Light Color)
(Dark Color)
Continents
Ocean Floor
Large crystals
(SiO2) rich
Large crystals
Fe, Mg rich
Small or no
crystals
(SiO2) rich
Small or no
crystals
Fe, Mg rich
IGNEOUS
 FELSIC
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
Light colored
Less dense
Rich in silica (SiO2)
Magma flows slowly, thick
Continental crust
IGNEOUS
 MAFIC
 Dark colored
 Very dense
 Rich in iron (Fe) and magnesium
(Mg)
 Magma flows quickly, thin
 Oceanic crust
IGNEOUS
 EXTRUSIVE
 “exit”
 Magma exits the Earth before
cooling
 Cools and crystalizes quickly
 Small or no crystals
IGNEOUS
 INTRUSIVE
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
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
“in”
Magma cools inside the Earth
Cools and crystalizes slowly
Large crystals
Igneous Rock Lab
 Use your Igneous observations sheet
 Rotate independently between the 25
stations set up around the room
 Start with whichever station number you
are located
 Round 1: You will have less than 1 minute
at each station
 Do not switch to the next station until told
to do so, only 1 person at at station (if you
have extra time, study your notes)
 Round 2: You may go back to any
unoccupied station, if needed