Mohs Scale of Hardness
Gemstones and other minerals are ranked according to their hardness. Hardness refers to a stone's ability to resist abrasion. A hard gemstone is not automatically tough or durable.
The Mohs scale of hardness is the most common method used to rank gemstones according to hardness. Devised by German mineralogist Friedrich Mohs in 1812, this scale grades minerals on a scale from 1 (very soft) to 10 (very hard). Because the Mohs scale is a relative scale, the difference between the hardness of a diamond and that of a ruby is much greater than the difference in hardness between calcite and gypsum. As an example, diamond (10) is about 4-5 times harder than corundum (9), which is about 2 times harder than topaz (8). Individual samples of a gemstone may have slightly different Mohs ratings, but they will be near the same value. Half-numbers are used for in-between hardness ratings.
A gem with a given hardness rating will scratch other gems of the same hardness and all gems with lower hardness ratings. Gold, silver, and platinum are all relatively soft, with Mohs ratings between 2.5-4. Since gems can scratch each other and their settings, each piece of gemstone jewelry should be wrapped separately in silk or paper. Also, be wary of commercial cleaners, as they may contain abrasives that could damage your jewelry.
I've added a few common household items to the basic Mohs scale to give you an idea of how hard gemstones really are and for use in testing hardness yourself.
