How Hard is that Rock? Moh's Scale of Hardness : Fizzics Education

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# How Hard is that Rock?

### You will need:

• Your fingernail (approx. Mohs Scale 2.5)
• An old 2-cent coin or copper penny (approx. Mohs Scale 3.5)
• An iron nail (approx. Mohs Scale 5.5)
• A hardened steel file (approx. Mohs Scale 7)
• Rock or metal samples eg. Granite, Marble, Iron, Zinc, etc

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Gently scrape each rock or metal sample with the above tools.

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Make sure you scrape along the sample with even pressure, length and material.

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Slowly work up Mohs scale until you find can scratch the sample, giving you an approximate hardness result.

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#### Get the Unit of Work on Geology here!

• The Earth’s layers, the rock cycle, volcanoes, earthquakes & more!

From soil science to mineral testing, these hands-on experiments your students will discover the importance of natural resources and the role of plate tectonics in shaping our world.

Includes cross-curricular teaching ideas, student quizzes, a sample marking rubric, scope & sequences & more

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### Why Does This Happen?

Rocks differ in hardness, due to the different compounds that make up the rock.

In 1822 an Austrian geologist, Frederick Mohs, devised a scale that ranked different mineral samples for their hardness, therefore standardising the field tests done by miners across the world.

Mohs chose the following samples as standards due to their abundance and different hardness.

1 = Talc, 2 = Gypsum, 3 = Calcite, 4 = Fluorite, 5 = Apatite, 6 = Orthoclase, 7 = Quartz

8 = Topaz, 9 = Corundum, 10 = Diamond.

By having a standard scale, prospectors can more easily classify the materials they find.