The Mohs Scale
Minerals, including gemstones, are rated and ranked according to their hardness. While hardness is generally associated with durability, the ability to resist breakage is better described as toughness. When referring to gemstones, hardness more accurately means the gemstone's ability to resist abrasion.
Regardless of which scale is used, the diamond is considered the hardest substance known to man. The most common measure of a gemstone's degree of hardness is based on the Mohs Scale. Devised by German mineralogist Friedrich Mohs, the Mohs Scale grades minerals on a comparative scale from 1 (very soft) to 10 (very hard).
Mohs Scale of Hardness
|6||Feldspar, Black Agate|
|6.5 - 7.5||Garnet, Black Agate|
|9||Corundum (Ruby and Sapphire)|
|Gemstone||Mohs Rating||Results from Grinding Test|
|Diamond||10||Approximately 90 times harder than corundum|
|Ruby/Sapphire (corundum)||9||Approximately 5 times harder than topaz|
|Topaz||8||Little difference between topaz and quartz|