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Rocks - Classifying Rocks
How Rocks Form
Geologists classify rocks into three major groups: igneous
rock, sedimentary rock, and metamorphic rock.
Rocks - Igneous Rocks
Classifying Igneous Rocks
Igneous rocks are classified according to their origin, texture,
and mineral composition.
Rocks - Igneous Rocks
Mineral Mixture
Granite is a mixture of lightcolored minerals, such as
feldspar and quartz, and darkcolored minerals, including
hornblende and different types
of mica. But granite can vary in
mineral composition. This affects
its color and texture.
Study the circle graph and then
answer the questions.
Rocks - Igneous Rocks
Mineral Mixture
Reading Graphs:
What mineral is most
abundant in granite?
Feldspar
Rocks - Igneous Rocks
Mineral Mixture
Reading Graphs:
About what percentage of
granite is made up of dark
minerals?
10%
Rocks - Igneous Rocks
Mineral Mixture
Calculating:
If the amount of quartz increases
to 35 percent and the amount of
dark-colored minerals stays the
same, what percentage of the
granite will be made up of
feldspar?
100% - (35% + 10%) = 55%
Rocks - Igneous Rocks
Mineral Mixture
Predicting:
How would the color of the
granite change if it contained
less feldspar and more mica
and hornblende?
The overall color would be
darker.
Rocks - Igneous Rocks
Main Idea
Igneous rocks are classified by origin, texture, and composition.
Detail
Extrusive rock forms
from lava on the
surface; intrusive
rock forms from
magma from beneath
the surface.
Detail
Intrusive rocks have
larger crystals than
extrusive rocks
because they cool
more slowly.
Detail
High-silica rocks are
light colored; lowsilica rocks are dark
colored.
Rocks
End of Section:
Igneous Rocks
Rocks - Sedimentary Rocks
From Sediment to Rock
Most sedimentary rocks are formed through a series of
processes: erosion, deposition, compaction, and
cementation.
Rocks - Sedimentary Rocks
Sedimentary Rocks
I. From Sediment to Rock
A. Erosion
B. Deposition
C. Compaction
D. Cementation
II. Uses of Sedimentary
Rocks
A. Building Materials
B. Tools
Rocks
End of Section:
Sedimentary
Rocks
Rocks - Metamorphic Rocks
Do you know……..
Q. Why do the crystals in gneiss line up in bands?
A. Gneiss is a type of metamorphic rock that is foliated—the
crystals are flattened to form parallel lines.
Q. How does quartzite form from sandstone?
A. High temperature and pressure on the minerals in sandstone
cause them to be changed into minerals that make up
quartzite.
Rocks
End of Section:
Metamorphic
Rocks
Rocks - The Rock Cycle
A Cycle of Many Pathways
Forces deep inside Earth and at the surface produce a slow
cycle that builds, destroys, and changes the rocks in the
crust.
Rocks
Graphic Organizer
Rocks
can be
Igneous
Sedimentary
Metamorphic
include
include
include
Intrusive
Extrusive
Clastic
Organic
Chemical
Foliated
Nonfoliated
Rocks - The Rock Cycle
Exit Quiz: Sequencing
Before you leave, and without using your notes from today,
draw the rock cycle, using the three types of rock below with
arrows.
Metamorphic
Igneous
Sedimentary