The Mohs Hardness Scale is a relative scale developed in 1812 by German geologist and mineralogist Friedrich Mohs. This scale is used to classify minerals according to their physical hardness and incorporates minerals commonly available in his day. Modern-day equivalents can also be used to test and determine the hardness of your unknown mineral. Your fingernail, a penny, piece of glass and a steel blade can be used to approximate the Mohs hardness of a mineral. The Mohs hardness scale is still used today to help students learn about physical properties in the world around us.
Instructions
1. Open your Mohs Scale mineral kit and examine the sample minerals. You should have 10 items in the kit, each mineral corresponding to a hardness ranking: talc (H=1), gypsum (H=2), calcite (H=3), fluorite (H=4), apatite (H=5), orthoclase (H=6), quartz (H=7), topaz (H=8), corundum (H=9) and diamond (H=10).
2. Examine the surface area of your test or unknown mineral sample. Look for a smooth, fresh surface.
3. Hold your specimen in one hand or secure it on a table. Hold your reference mineral in the other hand.
4. Scratch the smooth surface of your test mineral with a pointed edge of a reference mineral from your kit. Begin testing using your orthoclase (H=6) crystal.
5. Estimate the hardness of your sample mineral. If your mineral is scratched by the orthoclase you should see an etch line on the surface. This means that your mineral is softer than orthoclase (H=6).
6. Wipe the surface of your test mineral with your finger or a soft cloth to verify that the scratch is real.
7. Test the surface of your unknown mineral again using the next lowest hardness reference mineral, apatite (H=5). If apatite does not scratch the surface of your test mineral, the true hardness is between (H=5) and (H=6).
8. Use a steel blade, which has a hardness of about 5.5, and scratch the surface of your test mineral. If it is scratched, you'll know that the hardness of your test mineral is between 5 and 5.5.
9. Repeat the testing to be sure of your results. Use the same sequence of elimination in determining the hardness of other samples.
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