Download Igneous Rocks

Igneous Rocks
Igneous Rocks
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From the latin
word “ignis”
(which means
“fire”), igneous
rocks are those
that form from the
cooling and
crystallization of
magma
Composition
Igneous Rocks are made
up of minerals, and …
 Minerals are made up of
crystals, and …
 Crystals are made up of
atoms.
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Texture

Extrusive Igneous Rock: Fine-grained (small
crystals), igneous rock that cools quickly ON
Earth’s surface (think EXTERIOR)
Texture

Intrusive Igneous Rocks: Coarse-grained
(large crystals) igneous rock that cools
slowly beneath Earth’s surface (think
INTERIOR).
Ultimately, the texture is determined
by the rate of cooling
Magma vs. Lava

Magma is… molten material
found beneath Earth’s surface.

Lava is… molten material that
flows out on to Earth’s surface

Regardless of whether it is
considered magma or lava, it
contains the following
elements…

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oxygen
silicon
aluminum
iron
magnesium
calcium
sodium
Both magma and lava can cool
to form igneous rocks
Three factors involved in the
formation of magma…


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* temperature
* water content
* pressure
Three Types of Magma

Rhyolitic
 High
Silica
Content (about
70%)
 Creates
Explosive
Volcanoes
 Thick and
Chunky (like
oatmeal)
Three Types of Magma

Andesitic

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Medium Silica
Content (about
60%)
A mixture of
rhyolitic magma
and basaltic
magma
Volcanoes can be
mildly explosive
Three Types of Magma

Basaltic
Low silica content (50%
or less)
 Thin and runny (think
hot maple syrup)
 Volcanoes are not
explosive and lava flows
smoothly
 The Hawaiian Islands are
Shield Volcanoes, that
spill basaltic magma

Where this magma comes from
Bowen’s Reaction Series

An illustration that demonstrates how
minerals form in a predictable pattern as
magma cools.
Classifying Igneous Rocks

Felsic Igneous Rocks: Igneous rocks (such as
granite) that are light in color, have a high silica
(SiO2) content, and contain minerals such as
quarts, orthoclase feldspar, plagioclase feldspar.
Classification Cont…

Mafic Igneous Rocks: Igneous rocks (such as
gabbro) that are dark in color, have a lower silica
(SiO2) content, are rich in iron (Fe) and
Magnesium (Mg)
Classification Cont…

Intermediate Igneous
Rocks: A little bit of
both.

Ultra-Mafic Igneous Rocks:
Igenous rocks that have
a VERY low silica
content, and a VERY
high iron and
magnesium content
A Few Exceptions…

Porphyritic: An igneous rock that has
both fine-grained crystals AND
coarse-grained crystals.
Another Exception

Pegmatites: A vein of extremely large
crystals found in an otherwise finegrained igneous rock.
And one more…
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Kimberlites: A rare, ultra-mafic
igneous rock that contains diamonds.
Igneous Rocks in N. America
Plutonic
Volcanic