Download Igneous Rocks – 6.2

Igneous Rocks – 6.2
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Igneous rocks all begin as _magma/lava__
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Igneous rocks are classified (grouped) by two different factors:
o composition & texture

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Igneous rocks that form as magma cools underground are called: intrusive
Igneous rocks that form as lava cools on the surface are called: extrusive
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Colors of Igneous rocks
o Light colored igneous rocks probably contain a lot of light colored minerals such as:
Orthoclase feldspar
Quartz
o Dark colored igneous rocks probably contain a lot of dark colored minerals such as:
augite
biotite
horneblende
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Light colored igneous rocks come from _felsic_ magma, whereas dark colored igneous rocks
come from _mafic_ magma. You can remember that because “felsic” has the letter “L” for
“L”ight colored.
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Textures of Igneous rocks
Intrusive rocks like:
underground
Extrusive rocks like:
The surface
Typically have crystal
sizes that are:
Large and well defined
Because they cool so:
Typically have crystal
sizes that are:
_microscopic_ or
Because they cool so:
slowly
quickly
We call this type of
texture:
Coarse-grained
We call these textures
either _glassy_ or
_fine-grained_
_non-existant_
Some igneous rocks are full of
holes. This type of texture is
called “porous”. List the
names of those rocks to the
right.
Dark-colored
Light-colored
scoria
pumice
Explain how these igneous rocks formed with holes:
Gasses were trapped inside the rock as it solidified.
Igneous Rock Identification
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From your worksheet last class, write the names of the 7 igneous rocks below:
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You will rotate to each table in the room and write down facts about each rock. Then you
will try to identify it using the table on page 124. The word “felsic” usually means light
colored. The word “mafic” usually means dark colored. The only exception to this rule is
the rock, obsidian.
Table
Color
Texture
Name
1
2
3
4
5
6
7

Re-order your rock names in the table below:
IGNEOUS ROCK CHART
Texture
Glassy
Fine-grained
Coarse-grained
Porous
Light-colored (felsic)
rocks
Dark-colored (mafic) rocks