LESSON 4: HOW CAN WE TELL THE HARDNESS OF ROCKS? AIMS: 1. What is Moh's Scale of Hardness? 2. What is the scratch test? MOTIVATION: Have a sample of the following rocks on display for the children to touch: The first two rocks (talc and feldspar) were taken from http://ivyhall.district96.k12.il.us/4th/kkhp/RocksandMinerals/PinkFeldspar.html and the third picture, quartz, is from http://casdn.neu.edu/~geology/department/staff/colgan/iceland/minerals/quartz.htm The fourth sample, mica, is from http://cobweb.net/~bug2/rock4.htm The fifth sample, granite, is from http://ivyhall.district96.k12.il.us/4th/kkhp/RocksandMinerals/rocks.html PROCEDURE:1. Have students use their fingernails to see if they can make a scratch mark on any of the rock samples. Have them log on to http://ivyhall.district96.k12.il.us/4th/kkhp/RocksandMinerals/RockQuiz.html and read how they can judge the hardness of the various objects they will use to test their rocks. The following Moh's Scale of Hardness was taken fromhttp://cte.jhu.edu/techacademy/fellows/brannon/webquest/rmform.htm and the picture samples are from http://ivyhall.district96.k12.il.us/4th/kkhp/RocksandMinerals/RockQuiz.html The hardness of various rocks
and minerals can be used as an another method of identification.
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Hardness |
Mineral |
Scratched by . . . . |
1 |
talc |
soft pencil lead |
2 |
gypsum |
fingernail; blackboard chalk |
3 |
calcite |
copper penny |
4 |
fluorite |
iron nail; brass |
5 |
apatite |
steel knife blade |
6 |
feldspar |
window glass; steel file |
7 |
quartz |
flint sandpaper |
8 |
topaz |
spinel(available in rock shops) |
9 |
corundum |
emery sandpaper |
10 |
diamond |
carborundum sandpaper |
LAB ACTIVITY:
Problem:
How hard is a rock? Hypothesis: We think if we use our fingernail, penny, and an iron nail, then we can determine how hard a rock is. Materials: penny, nail, crayons, 5 rock samples, fingernail Procedure: 1. Label each rock 1, 2, 3, 4, 5. 2. Try to scratch each rock. Use your fingernail first, then the penny, and last, the nail. 3. Record what happened. Put an X on the chart of the rock was scratched. Observations: Use the chart to record your observations.
Answer the following questions: 1. How many rocks could you scratch with your fingernail?_________ Penny?________ Nail?_________ Conclusion: 1. Which rock was the hardest? How do you know? ________________________________ _________________________________________________________________________ 2. Which rock is the softest? How do you know?___________________________________ _________________________________________________________________________ _________________________________________________________________________ |
Click here for student samples of the Lab Activity.
Follow-up: This concludes the unit. From here, please click on assessments for culminating activities.
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