Download Name: ____________ Date: 8th Grade Science Earth Surface Mr

Name: ___________________________________ Date: ______________
8th Grade Science
Earth Surface
Mr. Vorstadt
Igneous Rock
Surface
Volcanic rocks are composed of very small
No Crystals
crystals because the molten rock has cooled
very quickly at or near the Earth's surface.
The rapid cooling does not give the crystals
Small Crystals
enough time to grow large. Volcanic rock is
sometimes called extrusive rock because
the molten rock (magma) is extruded at the
surface, where it is known as lava. For this
reason, all volcanic rocks have a fine grained Large Crystals
texture.
Fast cooling
Slow cooling
Very slow
cooling
Increasing Depth
All igneous rocks have formed by the
solidification of molten lava or magma
Plutonic rocks contain large crystals
because
Crystal Size and Cooling Rate
they have cooled and solidified slowly, deep
underground. The slower the magma cools,
the larger the crystals can grow Plutonic rock is also known as intrusive igneous rock
because it forms by slow cooling within the Earth.
Igneous rocks are classified on the basis of their crystal size and their mineral composition.
The felsic rocks are light in color and relatively low in density. They are rich in feldspar, a
light color family of aluminum silicate minerals. Mafic rocks contain more iron and
magnesium. Therefore, mafic rocks are usually more dense and darker in color than felsic
rocks.
Granite is a light colored, coarse grained plutonic rock. The large grains (crystal) make
individual mineral crystals readily visible without magnification. Granite is usually pink or gray
in overall color because of the abundance of feldspar minerals.
Rhyolite is light colored and it has a mineral composition like granite, but rhyolite is fine
grained due to rapid cooling and solidification. Magnification is required to see the individual
minerals crystals.
Obsidian is volcanic glass. It has cooled so rapidly that crystals could not form. Due to the
dispersal of the dark colored mineral, both mafic and felsic varieties of Obsidian are usually
dark in color.
Pumice is a volcanic rock so low in density that some samples may float on water. As
magma rises to the surface, gases trapped in the molten rock expand to form tiny air pockets.
.Although it doesn't look much like obsidian, pumice is actually a frothy form of volcanic glass.
Scoria is a rock full of larger air pockets, formed as gases expand within the cooling lava.
Scoria is more dense than pumice, and the bubbles are clearly visible.
Basalt is a fine grained, dark colored volcanic rock. Because it forms near the surface, basalt
is composed of very fine crystals. It is rich in iron and magnesium minerals, so it is dark in
color and relatively dense,
Gabbro is a dark (mafic) plutonic rock. It is coarse grained, like granite, but because it is rich
in iron and magnesium, it is dark in color. Gabbro is the coarse grained equivalent of basalt.
Use the chart on the other page and the descriptions on the igneous rock
to answer the following questions.
Earthqu
ake
Depth:
Earthquak
s are the
most
ommon
n zones
f crustal
ctivity.
Earthquak
s at great
epth
ndicate
elatively
ool
material
eing
rawn into
he Earth
t
ubductio
zones.
Plot these
eismic 18
eismic
vents by
rawing a
ark “X” at
he proper
ocations
n the
iagram
elow.
1. What name is applied to a coarse grained, felsic igneous rock? ________________
2. If granite rock was made of smaller crystals it would be called? ________________
3. What name is applied to a coarse grained, dark colored igneous rock? __________
4. What are the five minerals found in granite? _______________________________
__________________________________________________________________
5. Name the four minerals found in basalt and give the approximate percentages of each
mineral? _________________________
_____%
_________________________
_____%
_________________________
_____%
_________________________
_____%
6. Why do plutonic rocks have larger crystals than volcanic rock? ________________
__________________________________________________________________
7. According to the chart what is the texture of Pumice? ________________________
8. What is the fine grained rock similar in composition to rhyolite? ________________
9. What is the difference between rhyolite and granite? ________________________
10.
In order for igneous rock to formed the _________________________ and
_________________________.
11.
How large are the crystals of granite? __________
12.
What five minerals are commonly found in basalt? ________________________
________________________________________________________________
13.
How do extrusive rocks differ from intrusive rocks? ________________________
14.
What is the color of rhyolite? _________________________________________
15.
What is the approximate percentage of plagioclase in diorte? _______________
16.
What is the word (s) used to describe the grain size in pumice? ______________
17.
What two common minerals are found in granite, but not in basalt?
__________________________________________________________________
18. What igneous rock contains exceptionally large crystals?
__________________________________________________________________
Name: _____________________________________
8th Grade Science
Rocks & Mineral
Igneous Rocks
Date: __________
Mr. Vorstadt
There are
many kinds of rocks in the
Earth’s crust. These rocks are made up of different minerals.
Rocks can be grouped by the way they form. Igneous rocks form when hot liquid rock cools and
hardens. This process may take place inside Earth or on the surface. Inside Earth, magma cools so slowly that
is may take a thousand years for a rock to form.
One of the most common kinds of igneous rocks is granite. Granite is made by magma cooling inside
Earth. Granite is light colored with large crystals. It is made up mostly of the mineral quartz and feldspar.
Granite is strong and does not break easily, even under great pressure. It is often used in buildings and
bridges.
Basalt is made when lava pours onto the ground or into the ocean floor. Because the lava cools
quickly, the crystals in basalt are small. When lava erupts underwater it makes pillow-shaped lumps, called
pillow lava.
Sometimes, lava cools so quickly that crystals never have a chance to form. Pumice and obsidian are
igneous rocks that do not have crystals. Pumice is full of bubbles and is so light that it floats. Obsidian is a
glassy, black rock.
1. There are only a few kinds of rocks in the Earth’s crust. ______________
2. Rocks can be grouped by the way the form. ______________
3. Igneous rocks are formed when hot liquid rock cools and hardens. ______________
4. Basalt is made when lava pours onto the ground or the ocean floor. ______________
5. Sometimes lava cools so quickly that crystals never have a chance to form. ___________
B. Multiple Choice
______ 6. Rocks are made up of different (a) granite (b) minerals (c) lava
______ 7. Inside Earth, magma cools so slowly that it may take a -- ? -- for rocks to form.
(a) month (b) year (c) thousand years (d) million years
______ 8. Granite is made by magma cooling --? – Earth. (a) outside (b) inside (c) above
______ 9. Pumice is so light that it -- ? -- . (a) fizzes (b) erupts (c) floats
______ 10. Granite is light colored with -- ? – crystals. (a) large (b) small (c) no
C. Matching
_____11. Obsidian
A) used to make buildings and bridges
_____12. Granite
B) glassy, black rock
_____13. Basalt
C) so light it floats
_____14. Pumice
D) small crystals