Name: _____________________________________________
Date: ________________________
Rock Number
1
2
3
4
5
6
7
8
Lab Period: ________ Lab Day: _______
Texture
Coarse
Fine
Glassy
Composition
Felsic
Intermediate
Mafic
Igneous Rocks
Name
ESRT pg. 6
Minerals Present
ESRT pg. 6
QUESTIONS:
1.
Answer questions #1-5 in complete sentences.
2.
3.
4.
5.
6.
A
B
C
D
7.
A
B
C
D
8.
A
B
C
D
9.
A
B
C
D
10.
A
B
C
D
11.
A
B
C
D
Lab #9
Igneous Rock
INTRODUCTION: Please read this as it contains information that will help you
complete this lab successfully. Igneous rocks are rocks that form from the cooling of
molten magma (under ground) or lava (above ground). The word igneous means "fireformed." Cooling can be immediate or over long periods of time.
Rocks that form deep under the earth's surface cool very slowly. This slow cooling
allows crystals of individual minerals to form, producing a coarse texture (individual
minerals can be seen). These coarse-textured, slowly cooled rocks are called intrusive or
plutonic igneous rocks.
Rocks that form near the earth's surface cool quickly. This fast cooling does not allow
large crystals to form, producing a fine texture (individual minerals are difficult or
impossible to see). These fine-grained, rapidly cooled rocks are called extrusive or
volcanic igneous rocks. If the lava cools fast enough, no crystals form, resulting in
volcanic glass, pumice or scoria.
Igneous rocks are also classified by their composition (what they're made of). Some
igneous rocks are light in color and have a low density because they are rich in aluminum
(Al) minerals. These light colored igneous rocks are said to be of felsic composition.
Other igneous rocks are dark in color and have a higher density due to minerals rich in
iron (Fe) and magnesium (Mg). These darker igneous rocks are said to be mafic in
composition.
PROCEDURE: Fill in the Igneous Rock Identification Chart for each of the igneous
rocks in the rock kit.
TEXTURE:
Observe whether the rock has a coarse, fine or glassy texture.
Coarse textured rocks have easily visible individual
minerals (larger than 1 mm.).
Fine textured rocks have very small mineral crystals or
grains (smaller than 1 mm.). They might be salt and
pepper size or even smaller.
Glassy texture often looks like glass or sometimes it is
bubbly, containing lots of air pockets.
COMPOSITION:
Observe whether the rock is dark, light or of medium color.
When more than one mineral is easily observed, estimate the
proportions of dark versus light minerals.
NAME:
Use the Scheme for Igneous Rock Identification in your Earth
Science Reference Tables to identify the rocks.
Glassy and fine-grained rocks are found at the top of the chart,
and coarse-grained are found on the bottom.
Felsic rocks (light-colored and low density) can be found on the
left side of the chart and become increasingly more mafic (dark
and dense) to the right of the chart.
There are no peridotites or dunites in the rock kits.
MINERALS
PRESENT:
Once the rock is named, look at the chart below the rock's name
to determine what minerals are present. Whichever patterns can
be found in the zone below the name indicates the minerals
present. For example, granite, rhyolite, pumice and obsidian all
contain potassium feldspar, quartz, plagioclase feldspar, biotite
and amphibole.
QUESTIONS: Answer questions #1-5 in complete sentences.
1.
Explain how cooling rate effects an igneous rock's texture.
2.
Explain how the composition of igneous rocks effects the physical properties of the
rock. HINT: Include a discussion of its color and density.
3.
What minerals can be found in mafic rocks but not in felsic rocks?
4.
What minerals can be found in felsic rocks but not in mafic rocks?
5.
Explain the difference between lava and magma.
6.
Most igneous rocks form by which processes?
A)
heat and pressure
B)
melting and solidification
C)
erosion and deposition
D)
compaction and cementation
7.
According to the Earth Science Reference Tables, gabbro is composed mainly of
A)
hornblende and quartz
B)
biotite and olivine
C)
potassium feldspar and quartz
D)
plagioclase feldspar and pyroxene
8.
According to the Earth Science Reference Tables, which is a fine-grained igneous
rock made up primarily of potassium feldspar and quartz?
A)
rhyolite
B)
basalt
C)
granite
D)
gabbro
9.
Which igneous rock cooled the slowest?
A)
diorite
B)
rhyolite
C)
obsidian
D)
pumice
10.
An igneous rock which has crystallized deep below the Earth's surface has the
following composition: 70% pyroxene, 15% plagioclase feldspar, 10% olivine and
5% hornblende. According to the Earth Science Reference Tables, what is the
name of this igneous rock?
A)
rhyolite
B)
basalt
C)
granite
D)
gabbro
11.
Extremely small crystal grains in an igneous rock are an indication that the crystals
formed
A)
over a short period of time
B)
under high pressure
C)
from an iron-rich magma
D)
deep below the surface of the earth