Mineral hardness test: a 4th grade scratch lab with household tools

1. Write the Mohs scale from 1 (softest, talc) to 10 (hardest, diamond). Add the tools: a fingernail is about 2.5, a copper coin about 3.5, and steel is harder than both.
2. Model a test: press the fingernail firmly across the sample, then wipe with the cloth. A real scratch stays after wiping; a powder line from the tool rubs off.
3. In pairs, students test each mineral with the fingernail, then the coin, then the steel, recording yes or no for each.
4. Use the results to place each mineral: scratched by a fingernail means under 2.5, scratched by the coin but not the nail means between 2.5 and 3.5, and so on.
5. Students then try scratching the steel washer with the quartz. Ask: "What does it tell you that quartz scratches steel?"
6. Test the mystery sample and use the chart to narrow down what it could be.

Safety: students wear safety glasses, press firmly but do not dig, and never taste samples. Use a steel washer, not a knife, and skip glass plates.

Differentiation: students who need support test two minerals (talc and quartz) to see the two ends of the scale. Students who are ready add a streak test on the back of a white tile. English learners can use "___ scratches ___, so it is harder."

Quick check: ask: "A mineral is scratched by a coin but not by your fingernail. About where is it on the scale?" (Between 2.5 and 3.5.)

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