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The most common standard for rating gemstone hardness. Developed by Friedrich Mohs, a German minerologist, as an assessment of "scratch hardness" by ranking 10 different stones from hardest to softest. His list includes the following:
<br/>10. Diamond (hardest)
<br/>9. Sapphire
<br/>8. Topaz
<br/>7. Quartz
<br/>6. Orthoclase Feldspar
<br/>5. Apatite
<br/>4. Fluorspar
<br/>3. Calcite
<br/>2. Gypsum
<br/>1. Talc (softest)
<br/>Because the numbers are based on properties of actual stones, they are not equally distributed. So the difference between 10 (diamond) and 9 (sapphire) is not equal to the difference between any other two numbers. Very soft stones scratch more easily and some stones are too soft for jewelry.
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