Download Igneous Rocks - Aspen High School

Igneous Rocks
Reading: Chapter 6.2
Objectives:
Distinguish between intrusive and extrusive
igneous rocks and how they form.
Contrast the types of plutons that form as
the result of intrusive igneous activity.
1
Origins

Formed from cooled
magma or lava.
2
Origins

Knowing a rocks texture can help
determine it’s origin.

Intrusive: cooled inside the earth

Extrusive: cooled outside the earth
3
Intrusive
 PlutonicBatholiths
 solidified
deep underground
 coarse grained rocks
 mineral crystals had time to grow and
are visible to the naked eye.

This will produce a coarse grained or
porphyritic texture
4
Intrusive
5
Extrusive
form when magma cools at or near
the earth’s surface.
1. fine grained
2. glassy/frothy
3. fragmental
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Extrusive
7
Extrusive
8
Extrusive
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Identifying
Igneous
rocks are identified
according to their origin,
texture, and composition
10
Identifying
 Determine
the
texture- fine,
coarse,
porphyrytic,
glassy/frothy, or
fragmental
11
Identifying
Determine the color- light, medium, dark
 Light color= Felsic



Large amounts SiO2 and feldspar
Dark Color= Mafic
Large amounts of Fe and Mg
 Hornblende, augite, and biotite

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Felsic and Mafic
Felsic (light)
Mafic (dark)
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Identifying

What minerals can you see in the sample?
You can use comparisons in mineral abundance
to help determine rock type.

Eg: 50/50 Quartz to Feldspar

Granite
Syenite
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Coarse Textured Rocks are Hard!
Get it?

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
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
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Determine that it’s coarse
Then determine if light, medium, or dark
If light to medium, then you have to look at with
microscope
If there are two light colored minerals in equal
abundance (50/50), then it’s GRANITE
If there are two light colored minerals and there is more
of one than another (80/20), then it’s either MONZONITE
or GRANODIORITE (darker)
If there is only one light colored mineral AND it’s a light
colored rock, then it’s SYENITE
If there is one light colored mineral and it’s a dark
colored rock, then it’s DIORITE
UGH!!!!
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