Gemstone Hardness: The ability of a gemstone material to resist scratching and abrasion
Gemstone hardness indicated in Mohs’ scale
Gemstone hardness is one of the factors on which the durability of a gemstone depends. In gemmology, hardness is defined as the ability of a gemstone to resist scratching and abrasion. In relation to gem set jewellery, gemstone hardness is important as it indicates how well a gemstone will keep its polish during wear. The higher the hardness of a gemstone, the higher polish it will take and the longer it will retain that polish.
(NOTE: The hardness of a gemstone is a surface property and should not be confused with gemstone toughness: gemstone toughness is a body property which indicates the ability to resist fracture or cleavage.)
To indicate the hardness of a gemstone we use the Mohs’ scale of relative hardness. For Mohs’ scale, ten common minerals have been brought together in a list. Each material has its own consistent composition and hardness and they have been put in to order from 1 (extremely soft) to 10 (extremely hard). A mineral with a lower number will be scratched by one with a higher number. And of course vice versa: a mineral with a higher number will be able to scratch one with a lower number on the Mohs’ scale.
The hardness on Mohs’ scale indicates an order of relative hardness. For example: topaz, corundum and diamond are adjacent on Mohs’ scale, respectively with hardness 8, 9 and 10. But the difference in hardness between corundum (9) and diamond (10) is far greater than that between topaz (8) and corundum (9).