Moh's Hardness Scale
|1||Talc||Extremely soft, chalklike|
|2||Gypsum||Easily scratched with fingernail|
|3||Calcite||Difficult to scratch with fingernail|
|4||Fluorspar||Cannot be scratched with fingernail|
|5||Apatite||Similar in hardness to teeth|
|6||Feldspar||Hardness suitable for jewelry use|
|8||Topaz||Harder than any common mineral|
|9||Corundum||Twice as hard as Topaz|
|10||Diamond||Hardest, four times harder than Corundum|
Developed in 1822 by Friedrich Moh, a German mineralogist, this scale represents the relative hardness of selected minerals. Based on the premise that gem material higher on the scale will scratch lower ordered material, this scale has become the universal standard for describing 'hardness'
It should be noted that the hardness determined is not proportional. Diamond, for example, is many times harder than the next level, Corundum.