What is gemstone hardness?
Mohs scale of hardness is widely used to measure the hardness of gemstones. Created by German mineralogist Friedrich Mohs in 1822, each gem is assigned a hardness number. A gem is able to scratch another one with a lower hardness number. So a gem with hardness of 7 can scratch a gem with a hardness of 6.
These 10 gems are selected to represent the scale from 1 to 10 because they can easily be obtained in a highly pure form.