The Mohs scale of mineral hardness was developed in 1812 by Friedrich Mohs, a German mineralogist. There are several other methods of measuring mineral hardness but the Mohs scale is the best known by the general public. This method is technically a table rather than a scale since the relative hardness of the reference mineral is arbitrary. Here's use the Mohs scale of mineral hardness.
Instructions
1. Arrange 10 readily available minerals ranging in hardness from the softest to the hardest. Here are the minerals used by Mohs and their corresponding values: talc is 1, gypsum is 2, calcite is 3, fluorite is 4, apatite 5, orthoclase is 6, quartz 7, topaz is 8, corundum is 9 and diamond is 10.
2. Start with talc and try to scratch the mineral being tested with successively harder reference material until a scratch is made. For instance, if the test material cannot be scratched by quartz but is scratched by topaz, the test material has a Mohs hardness between 7 and 8.
3. Ensure that a scratch is actually made and is not just a mark that will rub off. The Mohs test may not be suitable if it only loosens grains without actually scratching the surface, which occurs with materials that are fine grained, friable or pulverulent.
4. Learn the approximate Mohs ratings for some common materials. A fingernail is 2.2, a penny is 3.2, a pocketknife is 5.1, a glass plate is 5.5, a steel needle is 6.5 and a streak plate is 7.
5. Be aware the Mohs scale is only used to gauge relative hardness. Other methods, such as the Knoop or Vickers hardness scales, are used to accurately measure a material's hardness.
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