1
Rock Labs 2013
Name
Date
Class
Crystal Size Demo: How are cooling rate and crystal size related?
Crystal size is directly related to the crystallization rate. In this demo, you will model crystal
formation under different temperature conditions.
Procedure
1. Read and complete a lab safety form.
4. Place a watch glass on top of each
beaker so its bottom is touching the water.
2. Mix 10 mL of warm water with
10 mg of Epsom salt (MgSO4).
Dissolve completely.
5. Pour 3 mL of the Epsom salt solution
in a graduated cylinder. Pour this
amount into each watch glass.
3. Completely fill three beakers with
hot, warm, or cold water. Label the
beakers.
6. Leave overnight. Record your
observations in your Science Journal.
Analyze and Conclude
1. Describe the crystals in each watch glass.
2. Infer In which watch glass did crystals form first?
3. Hypothesize How does your answer to question 2 relate to the cooling rate and crystal
size of igneous rocks?
4.
Key Concept Which watch glass represented the type of crystals found
in extrusive igneous rocks? Which one represented intrusive igneous rocks?
Extrusive Igneous:
Intrusive Igneous:
2
Skill Practice
Compare and Contrast
How do you identify igneous rocks?
Igneous rocks can be classified based on texture and mineral composition. The texture is dependent
upon cooling environment. When magma cools slowly beneath Earth’s surface, large crystals form.
When lava cools quickly on Earth’s surface, tiny crystals form.
In addition to texture, mineral composition is used to classify rocks. Color can be used to determine
whether a rock is rich in silica or metals. Geologists compare and contrast the texture and mineral
composition of igneous rocks to determine the processes that formed them.
Comparisons help scientists to classify unknowns when given only a description of their properties.
In this activity, you will compare and contrast a variety of igneous rocks and classify these rocks based
on detailed descriptions of their texture and mineral composition.
Procedure:
1. Use the data table on pg. 3 to record your data.
2. Obtain samples of granite and gabbro. These are both intrusive igneous rocks.
3. Using a magnifying lens, describe the crystal size and color of granite and gabbro and record
observations in your data table.
4. Now, obtain samples of pumice, basalt, and rhyolite. These are all extrusive igneous rocks.
5. Describe the crystal size and color of the extrusive rocks and record observations in your data table.
6. Finally, examine a sample of obsidian. Describe how this rock is different from other extrusive rocks.
Conclusions:
7. Think Critically Why do you think that obsidian (volcanic glass) differs from the other
extrusive igneous rocks? See p. 120 in the purple book
8. Infer Is an equal size piece of pumice less dense than rhyolite? Explain your answer.
See p. 120 in the purple book
9.
Key Concept How do the intrusive and extrusive igneous rocks differ? pp. 120-21
3
Igneous Rock Characteristics
Rock
Granite
Gabbro
Pumice
Basalt
Rhyolite
Obsidian
Texture=Crystal Size
Color
(large, small, none/glassy)
(light or dark)
4
Skill Practice
Observe
How are sedimentary rocks classified?
For millions of years, rocks on Earth’s surface have eroded with the help of water, wind, ice,
and gravity. Sediments are transported and deposited, settling to the bottom of rivers, lakes,
and oceans. Layers of sediment accumulate and undergo compaction and cementation and
become a sedimentary rock. In this activity, you will use a flowchart to identify different
sedimentary rocks.
Learn It
Scientists make observations to help develop hypotheses. In this activity, you will observe
the chemical and physical properties of sedimentary rocks to identify different rock types.
Try It
1. Use the purple book (pp. 125-129) & the flow chart to help you fill in the following table.
2. Obtain a sample of a sedimentary rock.
3. Use the flowchart below to complete steps 4–6.
4. Start at the top of the flowchart. If there are particles present, use a magnifying lens
to determine the size of the particles, to help identify the sample.
5. If the rock is smooth to the touch, test the sample with HCl (acid). Use a dropper to
place 1–2 drops of hydrochloric acid on the rock. If the sample fizzes with acid, it is
limestone. If it does not fizz, the sample is shale.
6. Fill in the data table on p. 5 to identify the formation & properties of the sedimentary rocks.
Do you see grains or pebbles?
Yes.
What are the
particles?
No. The rock is
smooth to the
touch.
Small grains
Large, rounded
grains
Sandstone
Conglomerate
Does not fizz
with acid
Shale
Fizzes with
acid
Limestone
5
Sedimentary Rocks
Rock Name
Does
ID each
this rock
type of rock:
Explain in general how the rock forms.
fizz with (Clastic, Chemical, or
vinegar? Biochemical / Organic)
Y/N
1. Rock salt
2. Conglomerate
3. Chert
4. Chemical limestone
5. Biochemical
limestone
6. Coal
7. Breccia
8. Rock gypsum
9. Sandstone
Directions: Answer the questions below.
7 . Explain why sedimentary rocks are usually uniform in color. See p. 128
8. Infer Why was an acid used in the lab? See p. 129
9.
Key Concept What characteristics can be used to organize sedimentary
rocks for identification? See pp. 127-129
6
Formation of
Sedimentary Rocks
Directions: Use your textbook to answer each question.
1. After sediment is eroded and then deposited by wind, water, or ice,
compaction and cementation can help form a sedimentary rock.
What are compaction and cementation? See p. 126.
2. Clastic rocks have a gritty texture like granulated sugar. The shape & size
of the clasts determines the environment the sedimentary rock forms.
What can the size & shape of the fragments tell you about the rock’s
formation? See p. 127.
3. Chemical sedimentary rocks can be made of crystals much like intrusive
igneous rocks.
How can you tell the difference between chemical sedimentary rocks and
intrusive igneous rocks? See p. 128
4. Biochemical rocks were formed by organisms or their remains.
What are some examples of biochemical rocks? See p. 129
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Lab A
Identifying the Type of Rock
Rocks can be classified into three major groups: igneous, sedimentary, and
metamorphic. Geologists examine rock texture and mineral composition to
classify rocks. Igneous rocks can be coarse or fine crystalline and multicolored or
glassy. Sedimentary rocks are often layered and contain a mix of rock fragments,
shells, minerals, and fossils. Metamorphic rocks can reflect a change in shape due
to an increase in temperature and pressure or the addition of chemical fluids.
Foliation (banding, layering) is common in metamorphic rocks. You will be given
rock samples to try and classify based on physical and chemical properties.
Question
How can the texture and the minerals a rock is made of be used to classify metamorphic rock?
Materials
metamorphic rocks (marble, gneiss, schist,
slate, quartzite, &/or phyllite ) HCl
(hydrochloric acid), and a dropper
Texture:
Rock
or Grain Size
(Large or Small)
Stripes/Bands?
Fizzes?
(yes/no)
(yes/no)
Procedure
1. Obtain a metamorphic rock and notice its texture and grain size.
2. Record your observations in the data table above.
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Lab A continued
4.Does the rock have parallel layers? If so, it is a foliated metamorphic rock.
If not, it is nonfoliated.
5. Use a dropper to place 1–2 drops of vinegar on the rock. If it fizzes,
the rock contains the mineral calcite.
6. Repeat the classification steps with another metamorphic rock.
Now that you are done with all three labs:
7. Design a flowchart in your notebook for identifying rocks that includes
all three rock types (igneous, sedimentary, and metamorphic) and the
characteristics you have used in each of the 3 rock identification labs.
Characteristics may include texture/size of grains or crystals, color,
relative density, and whether it fizzes with vinegar or not.
** For ideas, go to http://www.rockhounds.com/rockshop/rockkey/ or packet p. 4
8. Experiment with your flowchart as you classify rock samples brought in from home.
9. Refine or make changes to the classification flowchart as needed so it works for all
samples that you are given.
10. Identify the unknown samples and include their names in the flowchart that you made.
Lab Hints:
• Remember that the light or dark colors of a rock can lead to the identification
of minerals in the rock.
• Rocks that fizz when acid, such as vinegar, is added to them contain the mineral
calcite. Examples of such rocks include limestone and marble.
Analyze and Conclude
11. Describe how some samples were more difficult to classify than others.
12. Explain which characteristic was the least helpful in your flowchart.
13. The Big Idea What characteristics made it easier to classify rock samples?
Communicate Your Results: Transfer your final flowchart onto a whiteboard to share
with your class. Be sure to label the characteristics and the choices at each step in the chart so it
is easy to follow.
9
Rock Collecting and Classifying
**Bring in 2 rocks from around your house—they need to fit in the palm of one
hand and be large enough to see the characteristics!
Try to collect a variety of different types of rocks-- igneous, sedimentary, and
metamorphic. Use a data table like the one below to describe and classify each
rock in your collection. Add to your table as needed.
Rock Collecting and Classifying Data Table
Sample
& who
brought
it
A
B
C
D
E
F
G
H
Color
Texture=grain size
(Large or Small)
Banded or
Not
Fizzes with
acid?
Y/N
Rock Type