Pet Rock

Science/Math

Objectives

• Students will use hand lenses for close observation.
• Students will observe and record data about their rocks.
• Students will make predictions about their rocks.
• Students will test and compare their predictions with the measured/tested results.
• Students will measure the length and mass of their rock.
• Students will be introduced to the Mohs' hardness scale.
• Students will find out if calcium carbonate is present in their rock.

Materials

• 1 rock per student
• 2 or more metric rulers
• 2 or more scales with gram weights
• 2 or more copper pennies
• 2 or more steel nails
• Water container
• 100 ml of vinegar
• Hand lenses
• Various additional rocks for comparison, such as lava, pumice, etc.

Procedure

1. Have each student bring a rock bigger than their thumb and smaller than their fist. Encourage them to bring interesting and unusual rocks.
2. Bring in samples of soft rocks, such as lava or pumice for comparison.
3. Use these samples to model the activities for the students.
4. Set up centers for the different comparisons.
5. After teacher has modeled the activity, students will first observe their rocks and write down at least 5 observations at their table groups before they travel to the different centers.
6. Students will make their predictions and draw a picture of their rock on the worksheet.
7. Centers:
   1. Length/Mass
      Measure and record the length and mass of rock
   2. Scratch Test
      A scratch is defined as a small crevice. Pressure should be applied. Traces of metal are not scratches. Try the scratch test in this order: fingernail, penny, nail.
   3. Vinegar Test
      Use an eyedropper to place a few drops of vinegar in a scratch or on the surface. If it bubbles, calcium carbonate is present, which is found in limestone and marble.
   4. Sink or Float?
      Place the rock gently in water and see if it will float.
8. After completing all the centers, students will write a sentence about each center, at their table groups, to describe the characteristics of their rock and the comparisons of their predictions and test results.
9. Discuss the various tests. Discuss what the students think about different rocks sinking and floating, why some rocks bubble in vinegar, and similarities and differences between rocks.
10. Introduce the students to the Mohs' hardness scale. Help them to find the hardness of their rocks.
11. Tell the students that if their rock bubbled when vinegar was dropped onto it, that it contains calcium carbonate. Discuss and show examples of rocks that contain calcium carbonate.

Evaluation

1. Did the students carefully observe their rocks using hand lenses?
2. Are the students recording the data and observations they are making?
3. Did the students make logical predictions about the characteristics of their rocks?
4. Can the students perform the tests accurately? Are they comparing what they predicted with their test results?
5. Can the students accurately find the mass and length of rocks? Do they need help manipulating the balances and rulers?
6. Can the students identify the hardness of their rock on the Mohs' Hardness scale?
7. Can the students say whether or not their rock contains calcium carbonate by the presence of bubbling with vinegar?