The Composition of Rocks and Minerals

NC Standard:  2.02

Activity:  How Hard Is Your Rock?

Question: Do rocks vary in hardness?

Vocabulary: Hardness scale

Materials: Various rocks, dull knife, nails and other items that will scratch

Background: This activity can be done using the same collected rocks used in the classification activity.

Procedures: Divide the students into collaborative working groups of 3 or 4. Provide each group with an assortment of different rocks.
Have the students select two rocks from their assortment and attampt to scratch one of the rocks with the other. Have the students record their results and hypothesize which one of the rocks is harder, the one that can be scratched or the one that scratches?
Keep the harder rock and put the other rock to the side for the moment.
Choose another rock from the assortment and repeat the same scratch test using the first rock that was kept.
Keep the harder of the rocks and continue until the team determines that hardest rock of their collection.
Now have the teams compare the other rocks to find the second, third, fourth hardest rocks. These should be lined up next to the hardest rock until all the rocks have been lined up in order of their hardness.
The scratch test can be used to compare other items. Which is harder, a nail or a rock? A penny or a rock?

Evaluation: Have the students find other rocks which are harder / softer than ones in their assortment.
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Line of Learning:  This line is drawn to provide students with a space to share their experimental learning in words or pictures.
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