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Testing rock hardness

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


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

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

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

Why Does This Happen?

Rocks differ in hardness, due to differing 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 begin to classify the materials they are finding. 
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