Name ___________________________________ Date _______________
Class Period _____
Instructor _____________
Lab Period ______
5 points
Igneous
Igneous Rock Identification Chart
Rock Number
I1
I2
I3
I4
I5
I6
I7
I8
I9
I10
Texture
1 point each
Composition
1 point each
Name
3 points each
Minerals Present
1 point each
QUESTIONS:
1.
3 points each. Answer questions #1-5 in complete sentences. No pronouns.
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 #14
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 "fire-formed." 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.
Coarse rocks are found at the top of the chart, fine below coarse and
glassy rocks 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. No pronouns.
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