Igneous Rocks
Vanderbilt Student Volunteers for
Science
Fall 2013
1
Introduction
• There are 3 types of
rocks:
– Sedimentary
– Metamorphic
– Igneous
What are igneous rocks?
• Igneous rocks form when
the melted rock material
from inside the Earth
cools.
• This cooling and
hardening of melted rock
material can occur both
on and underneath the
Earth’s surface
Pass out the Volcano
Handout Refer to its
images as you discuss key
terms
2
Introduction
Lava
VS
Melted rock on or above the
Earth’s surface.
Extrusive Rock
Extrusive igneous rocks:
formed from lava on or
above the Earth’s surface.
Magma
Melted rock underneath the
Earth’s surface.
VS
Intrusive Rock
Intrusive igneous rocks:
formed from magma
underneath the Earth’s
surface.
3
Examining Igneous Rocks
A. Intrusive vs. extrusive
igneous rocks
1. Hand out the igneous rock
mats and igneous rock
samples
2. Have students place rocks
on corresponding spots on
the mat. Help them as
needed.
3. Explain that all these rocks
are igneous, and show which
are extrusive and which are
intrusive
4
Examining Igneous Rocks
4. Ask students:
1. What differences do you see
between the intrusive and
extrusive igneous rocks?
Extrusive are solid colors while
intrusive are ‘speckled’
2. What are the differences
among the 3 columns?
Color from left to right gradually
gets lighter
5. Explain the columns:
1. Blue: Felsic rocks – contain
silicon, sodium, aluminum,
potassium
2. Red: Mafic rocks – contain
calcium, iron, magnesium
3. Gray: Contains minerals found
in both felsic & mafic rocks
5
Examining Minerals of Igneous
Rocks
B. The minerals of igneous
rocks
1. Remind students that minerals
are the building blocks of rocks
2. Hand out the mineral rock sets
and magnifying glasses
3. Explain the Venn diagram:
1. Blue circle: minerals found in a
felsic/granite rock
2. Gray circle: minerals found in
an intermediate rock
3. Red circle: minerals found in a
mafic/basaltic rock
4. Overlapping areas: minerals
are found in both types of
igneous rocks
6
Examining Minerals of Igneous
Rocks
4. Ask students:
1. What differences in color do
they see?
Color gets lighter from left to
right
2. What is the relationship
between the color of the
mineral and the color of the
rocks?
Color of rock depends on color
of minerals that make it up
3. Which type of igneous rock
(extrusive or intrusive) is it
easiest to identify the
minerals that make it up?
Intrusive because you can see
the different crystals
5. Spend 3 minutes examining
the rocks to find minerals.
7
Examining Pegmatite
1. Hand out pegmatite samples
– Pegmatite is igneous rock with
large mineral crystals. It does
not have a specific mineral
composition.
2. Have students identify what
type of igneous rock their
sample of pegmatite is by:
1. Based on its appearance,
decide if it is intrusive or
extrusive
2. Closely examining the
minerals in the pegmatite
3. Based on minerals they can
identify, determine whether it
is granitic, intermediate, or
basaltic
Answer:
Intrusive rock (large crystals)
Felsic or intermediate (depending
on minerals seen)
Granite or Diorite
Special Types of Volcanic Rocks
1. Tell students they will look at
special volcanic rocks, which
are different from the igneous
rocks that they have already
looked at
2. Hand out volcanic rocks and
volcano diagram.
3. Tell students to make
observations about each rock,
and to fill in their observation
sheets
4. Working through each rock,
discuss the students’
observations and what makes
each rock unique
5. Collect all rocks and put them
into the corresponding cases
in the labeled positions
9