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Gemstone hardness is commonly measured using a scale called Moh’s scale. It derives its name after Friedrich Moh’s, a German mineralogist who in 1822 devised a crude but practical method of comparing hardness or scratch resistance of minerals.

Moh’s designed a brilliantly simple scale, or rather table that easily test the hardness of a mineral. Moh’s took 10 well known and common minerals and arranged them in order of their scratch hardness. Simply put, if one mineral could scratch another mineral then it is harder than that mineral.

Hardness	Mineral
1	Talc
2	Gypsum
3	Calcite
4	Fluorspar
5	Apatite
6	Feldspar
7	Quartz
8	Topaz
9	Corundum
10	Diamond

While it may not be too practical, or affordable, for the every day gemstone dealer to perform self tests, Moh’s scale is still of great importance for the gemstone buyer. Generally, high scratch resistance is desirable for gemstones and a Moh's hardness of 7 or higher is important.

The principal reason is that a common cause of abrasion is sand, which is silica grit (quartz), and is commonly present in dust. Stones which are softer than quartz are not suitable for everyday jewelry. Some gems however such as pearls and opal are quite soft, but are usually polished into cabochons or beads, rather than facetted, and therefore do not show scratches so easily.

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