Igneous Rocks - www .alexandria .k12 .mn .us

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Types of Rocks
Objective #1: Describe and classify igneous rocks
Agenda:
1. Journal entry: What does the word igneous mean?
How do igneous rocks form?
2. Review webquest and directed reading
3. Notes on igneous rocks
4. Identify and describe samples
3 Major Rock Groups
3 Major (Geologic) Rock Groups
Not the Rolling Stones, Kiss, or Van Halen
Igneous Rock
Sedimentary Rock
Metamorphic Rock
Identifying Rocks
Igneous pattern
Metamorphic pattern
Sedimentary pattern
-Forms when hot, liquid, magma crystallizes (cools
and solidifies).
Magma forms 3 ways:
1.
Rock is heated
2.
Pressure released
3.
Change composition
Basalt lava (glowing rock) oozes over basalt lava flow
Holt Online Visual: Comparing Int. & Ext Igneous Rocks
A. Igneous Rock
a.
Intrusive Igneous Rock
-Forms inside Earth
-slow cooling
b. Extrusive Igneous Rock
-Forms on surface (exterior) of Earth
-Fast cooling
a. Composition of Igneous Rock
Felsic Rock
-Light colored
-made of aluminum,
potassium, silicon, and
sodium.
Mafic Rock
-Dark colored
-Made of calcium, iron,
and magnesium.
Course-grained
Course-grained
Fine-grained
Fine-grained
b. Texture of Igneous Rock
-Slow cooling forms
large crystals.
(Coarse-grained
Texture)
-Fast cooling forms
small crystals. (Finegrained Texture)
-Rate of cooling
influences crystal size.
Fast cooling = small crystals
Slow cooling = large crystals
Show Holt Visual: Igneous Rock Texture
Pop Quiz!
What size crystal forms from extrusive rock?
2. What is one way magma forms?
3. Generally speaking what color are felsic rocks?
4. Quality of rock based on the size,
shape, and arrangement of grains is
referred to as…
5. What are the 2 characteristics that geologist
study to identify rock:?
1.
Rock ID practice
Use the rock key to identify the various rocks on your table:
Igneous Rocks

Classified according to composition & texture
 Glassy- shiny and look like glass, not
organized into crystals.

Ex: obsidian
Fine-grained-made
Ex:
of interlocking crystals.
basalt
BASALT
More Igneous Rocks…
Course
Grained
TextureGranite
More Igneous Rocks…
Porous- no crystals, cools rapidly, looks
like a sponge.

Ex: pumice
More Igneous Rocks…
Diffferent size crystals locked together
More Igneous Rocks…
Sedimentary Rock
Strata layers of rock.
Stratification The process in which sedimentary rocks are
arranged in layers.
Holt Visual Sedimentary Rock Cycle
3 Types of Sedimentary Rock
1. Clastic forms when rock or mineral fragments are
cemented together.
2. Chemical forms when minerals crystallize out of
solution, such as sea water, to become rock.
3. Organic forms from the remains of once-living plants
and animals.
Ex: Limestone
Coal
Chalk
Metamorphic Rock
-Rocks that have undergone a change in texture, structure,
or composition.
-Changes in heat and pressure cause rocks to change from
one form to another.
Origins of Metamorphic Rock

Contact
Metamorphism

Rock undergoes
metamorphism
when it comes in
contact with magma
or is heated by
nearby magma.
Regional
Metamorphism
-Pressure builds up in rock
that is buried deep below
rock formations or when
large pieces of rock
collide.
Textures of Metamorphic Rock
Foliated the texture of metamorphic
rock in which the mineral
grains are arranged in planes
or bands.
Nonfoliated
-The texture of
metamorphic rock in
which the mineral grains
are not arranged in
planes or bands.
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