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This lesson introduces Moh’s Hardness Scale to test the Hardness of a Rock




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Title – Moh’s Hardness Scale
By – Scott Dan
Subject – Science, Art
Grade Level – 1st – 2nd
Concept: Cardinal Numbers and Moh’s Hardness Scale

Materials: Variety of rocks, penny, pocketknife, nail, steel file, identification charts (see
preparation), wet cloth, book “Let’s Go Rock Collecting by Roma Gans,
colored dots or markers, 12 x 18 sheets of paper,

Preparation: Prepare 5 identification charts. Each chart consists of two 12 x 18 sheets of
paper taped together the long way. The chart will have the numbers 1 -10
evenly spaced out from beginning to end.
Day One:
1. Gather children into one large group.
2. Hold to rocks up for the children to see. Ask the children to please tell you all the ways that they know of to identify, sort, or organize these two rocks. List these on a piece of large chart paper.
3. Next, ask the children to tell you how you can tell if one rock is harder than the other. Listen to the children’s ideas, and test any of their hypotheses. A few of these tests might include chipping the rock with some sort of tool, banging the rocks together, or tapping the rocks to hear what sound they may make.
4. Group students into fours and provide each group with 10 rocks. Ask each group to come up with as many ways as they can think of to test the hardness of the rocks, and to put them in order from weakest to strongest. Ask them to keep their rocks in this order when they are finished so that the rest of the class can observe what everyone has done.
5. Provide them with 15 minutes for this exploration time.
6. Have the class go from station to station to observe what each of the groups have done.
7. Gather for a whole group discussion.
8. Ask the children what they did to sort the rocks by hardness.
9. Ask if size was important. Color? Shape? Smell?

Day Two:

1. Break the children into groups of four. Provide each group with a set of rocks, a penny, dull butter knife, nail, a steel file, and a damp rag.
2. Write the following on the board:
Thumb rubbing – 1
Fingernail – 2
Penny – 3
Butter knife – 4
Nail – 6
Steel file – 8
3. Give each group an identification chart.
4. Ask the children if they know what they are going to use the following tools for along with their rocks. If no one knows, remind them of yester day’s experiments.
5. Explain and demonstrate what each of the numbers mean. Also talk about safety precautions. When a child tests a rock, and it makes a mark with one tool, but not with the one above it, the child is to place the rock on the number that matches the tool that marked the rock. After each test, have them use their rag to clean out any small particles that may be hiding the mark.
6. After all of their rocks have been placed, have the class go around to each of the stations and examine what the different groups have.
7. Gather for a whole group discussion.
8. Ask the children what rock was the hardest. (If the teacher wishes them to know the rock by name, or wants them to be able to identify the rock in some way, then the teacher may either use masking tape to write the name on the rock, or color code each of the rocks with markers or colored circle stickers.)
9. How do you know that that rock was the hardest? (it used a tool that was highest on the scale, or it was the highest number)
10. What was the softest rock? How do you know? (it used a tool that was lowest on the scale, or it was the lowest number)
11. What was a rock that was not as soft as the softest rock, but not as hard as the hardest rock? How do you know? (it used a tool that was in the middle of the scale, or it used a middle number).
12. What did the numbers on the identification chart help you to do in this experiment? (to determine the hardness of the rock by comparing them against other rocks/numbers)
13. Does anyone know what these numbers are called when they help us determine the hardness of a rock? (Moh’s Hardness Scale).
14. Show a large picture of Moh’s Hardness Scale from the book, “Let’s Go Rock Collecting,” by Roma Gans.
15. Ask the children to explain why we did not have any materials in class to test number 10 on the scale.
16. Ask the children what number on the scale does chalk fall into.
17. Set up an area in the room as a center to allow the children to explore this concept further. Have a smaller scale identification chart, picture of Moh’s Hardness Scale, along with several rocks and tools to test the rocks and organize them according to strength. At center time, have children record their results. The teacher may do this by color-coding the rocks with either colored circle stickers or colored markers. The children will be provided with a piece of paper that looks like a time line. They will be provided with either colored markers or circle dots to place on their scale to represent where each rock falls on the scale.

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