IGNEOUS ROCKS (variation of the activity in GEMS)
The purpose of this lab is to introduce the concept of igneous rocks. Students will discuss the
properties of igneous rocks and observe examples of rocks. Students will also use Salol to
recreate rock crystallization.
Materials: Note- read through and practice first to get the hang of Salol!!!
Rock Box:
Same idea as the mineral box. You can use the following igneous rocks (again from Ward’s):
Granite, rhyolite, basalt, gabbro, pumice or scoria are optional
(If you are doing the sedimentary lab you may want to order sedimentary rocks at the
same time- sedimentary rocks are NOT necessary for the sedimentary lab, but are nice for
students to see)
Hand lens
Salol (phenol salicite—I think). You get this from Ward’s and you will only need one bottle.
Tin can or something disposable to heat salol in.
Hot plate
Disposable spoon to distribute salol.
Wax paper squares (2 for each group)
Small bowl for each group to put ice in
Ice
Review:
1. Does anyone remember what geology is?
2. So far in our geology unit we have talked about plate tectonics and minerals. Does
anyone remember the basic idea behind plate tectonics?
3. And what are the ways these plates can move? Someone use their hands and show me
one-way. And what is this plate boundary called when the plates move_______? (See
below) And what things do you find at this type of plate boundary?
Together —
Subduction — Volcanoes, Earthquakes
Collision — Mountains
Apart —
Spreading — Ridges forming new rock
Past one another— Transform — Earthquakes
Invitation:
1. Has anyone here ever gone climbing on rocks? Where?
2. Do you think there are any rocks in Florida? What kind? (Limestone)
3. What kinds of things can you tell me about rocks? Can anyone guess any of the three
rock types?
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Exploration:
1. Ok, who got to see their new salt crystals? What crystal shape did they have? (Cube)
2. Was this the same as their crystal shape before the salt crystals were dissolved in water?
(Yes) Why? (It is a characteristic of a mineral that all crystals have the same original
crystal pattern)
3. What are the characteristics of a mineral?
1. Non-living, 2. Specific properties, 3. Definite chemical composition, 4. Crystalline
structure, 5. Naturally occurring
So they had the same shape because a mineral will always grow the same crystal shape if it has
room.
4. What happens if it doesn’t have room? Did you see any in your cup that didn’t have room
to grow all the way? What did they do? They merged around each other. This is the same
thing that minerals do when they grow to form rocks. When they come into contact with
other minerals they have to try to grow around them.
5. Can anyone tell me the difference between a rock and a mineral? Rocks can be made of
many minerals (but they don’t have to be)
6. Does anyone know the names of any rocks?
Today we are going to be studying igneous rocks. We are going to make two igneous rocks and
explore how they are formed. Take a look at rocks A-D in your box. (A-Granite, B- Rhyolite, CGabbro, D-Basalt) You can remove these four rocks and put them on your desk.
7. What observations can you make about these rocks?
8. Color—What do you think makes the color in these rocks? The minerals in them.
9. Look at granite. You can see crystals of individual minerals. Do you see crystals in all
four of the rocks? What ideas do you have about why you can see crystals well in some
but not in others?
We are going to find out. Put the salol on hotplate to melt and give each team two pieces of
wax paper and one bowl.
I have melted these minerals to make magma. I am going to put this magma on your wax paper
and I want you to observe what happens. Put small amount of salol on each team’s wax paper
(not on ice yet).
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What did you see? So the rocks crystallized from molten magma. This is how igneous rocks are
formed. You have to have a melt and as that melt cools, the minerals crystallize out to form
rocks. What do you think would happen if the magma cooled at a lower temperature?
Put a piece of ice in each team’s bowl. Put your wax paper over your ice so that when I put the
magma in your ice will be directly under it to cool it quickly.
1. What did you observe this time? Which cooled and crystallized faster: the magma at
room temperature or the one on ice?
2. How does the one that crystallized faster compare to the one that had more time to cool?
3. So the amount of time that a magma has to cool can determine the size of the crystals.
Which magma has larger crystals, one that cools quickly or one that cools slowly?
4. A magma that cools slowly has larger crystals that you can see with your naked eye. One
that cools quickly has smaller crystals. Why do you think this is? The more time a crystal
has to grow the larger it can get.
Concept Introduction:
1. Compare the rocks you made with the four igneous rocks in your box (A-D). Which do
you think cooled slowly? Granite, Gabbro. Why? Larger crystals
2. Which do you think cooled quickly? Rhyolite, Basalt. Why? Smaller crystals make
minerals hard to see.
3. Can you think of any place on earth where magma pushes through the crust to become
lava and cools quickly? Volcanoes, spreading ridges
4. If it cools quickly, will you be able to see the minerals easily? No.
5. So which rocks in your set came from volcanoes or spreading ridges? Rhyolite, Basalt.
The lava to make these rocks extrudes from, or comes out of, the earth. Remember that below the
solid crust there is a molten mantle with magma in it. Sometimes it makes its way to the surface
of the earth. Because it extrudes, these rocks are called extrusive, or rocks that were formed
outside of the earth’s crust.
Rocks that don’t explode out of the crust cool slowly. Remember it is much hotter as you get
closer to the mantle. Intrusive rocks stay inside the crust until the rock has completely
crystallized. We can’t see them as they form. We have to wait millions of years until these huge
pockets of rock are exposed by plate tectonics and erosion. The mountains at Yosemite are
actually huge pockets of intrusive rock that cooled inside the earth and were later exposed.
6. Which of your rocks are intrusive rocks? Granite, Gabbro
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Application:
So we’ve seen that the crystal size in a rock depends on whether it formed intrusively (inside the
earth) or extrusively (outside the earth). Crystal size separates the rocks into two groups. What
else would separate the rocks into groups?
We’ll talk more about this tomorrow.
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Rocks
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
Rocks
Rocks
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
Rocks
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
Rocks
Rocks
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
Rocks
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
Rocks
A- Granite
B- Rhyolite
C- Gabbro
D- Basalt
J- Mudstone
K- Sandstone
L- Conglomerate
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