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Frequently Asked Questions (FAQ) / Gemstone Hardness Scale

What is the scale used to measure the hardness of gemstones?

The Mohs scale of mineral hardness was created by the German mineralogist Friedrich Mohs in 1822 to measure the relative hardness or scratch resistance of various minerals. He based it on ten readily available minerals. The hardness of a material is measured by finding the hardest material that that the given material can scratch, or the softest material that can scratch the given material. For hardness ratings on all the different gemstone varieties see our gem hardness chart. For more information on Mohs, see our article on Friedrich Mohs.

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  • First Published: February-20-2006
  • Last Updated: November-10-2014
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Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart