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The Minerals in Rocks
LA
O
RY
17
T
BO RA
Y
ou now know that minerals like diamonds and calcite come
from the earth. You might be surprised to find out that the crystal
size of most minerals is very small. Look at a rock—can you see its
individual crystals? Rocks are made of minerals, and the size of each
particle is pretty small.
Rocks can often be identified by the minerals that they contain. Each
rock may contain one or many different minerals. In this activity, you
will investigate two rocks: granite (GRAN-it) and limestone. Each rock
contains one of the two minerals you investigated in the last activity,
either calcite or quartz.
CHALLENGE
Can you identify one of the minerals found in a rock?
The mineral olivine (above), which is sometimes
cut and polished into the gemstone peridot, is
found in both of the rocks shown at right. The
size of the mineral crystal in the rocks is much
smaller than in this specimen of the mineral.
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Activity 17 • The Minerals in Rocks
MATERIALS
For the class
copper strips
glass scratch plates
white ceramic streak plates
30-mL bottles of 0.5 M hydrochloric acid
cups of water
droppers
SEPUP trays
paper towels
safety goggles
For each group of four students
2
magnifying lenses
1
piece of granite
1
piece of limestone
For each student
1
Student Sheet 17.1, “Rock Observations”
SAFET Y
The hydrochloric acid solution can cause skin irritation and
damage clothing. Always handle acids carefully and wear safety
goggles. Wash your hands after completing the activity.
B-26
The Minerals in Rocks • Activity 17
PROCEDURE
1. Work with your partner to examine one of the rocks carefully,
using a magnifying lens.
2. Record your observations on Student Sheet 17.1, “Rock Observations.” Based on what you saw, write whether you think the rock is
made up of one mineral or more than one mineral.
3. Switch rocks with the other half of your group and repeat Steps 1
and 2.
4. Each rock sample contains either calcite or quartz. Discuss with
your partner which property you would most want to test to identify the mineral in each rock. You can only choose one property.
Hint: You may want to review the data in Table 1, “Mineral Properties,” from Activity 16, “Mineral Identification,” to review the
properties of calcite and quartz.
5. Record the one property that you would like to test on Student
Sheet 17.1. Plan to test the same property on both rocks.
6. Obtain your teacher’s approval of your plan.
7. Gather the materials and perform your test. Be sure to record your
results on Student Sheet 17.1.
8. Exchange rocks with the other half of your group and repeat the
test for the other rock.
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Activity 17 • The Minerals in Rocks
ANALYSIS
1. Which mineral—calcite or quartz—is found in granite rock? Support your answer with evidence from your investigation.
2. Which mineral—calcite or quartz—is found in limestone rock?
Support your answer with evidence from your investigation.
3. How do the rocks you have observed look different from minerals
you have observed? Explain.
4. Copy the three lists of words shown below.
List 1
List 2
List 3
fluorite
rock
limestone
quartz
property
granite
mineral
streak color
calcite
granite
transparency
rocks
diamond
luster
a. Look for a relationship among the words in each list. Cross out
the word in each list that does not belong.
b. Circle the word in each list that includes the others.
c. Explain how the word you circled relates to the other words in
the list.
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