Hardness in jewelry terms (and gemology) means the ability of a subject to withstand abrasion by another subject. The most widely used scale of hardness (in gemology) is Moh’s scale of relative hardness. This scale is from 1 to 10 with gypsum rated at a 1 and diamond rated at 10. A material – or gemstone – that is lower on the scale can not leave a scratch on a material that is higher on Moh’s scale. Quartz (at place 7) is a critical point as dust in the air has many minute silica particles in it and may scratch gemstones and other materials below place 7 on the hardness scale. Sand also consists in part of quartz and may cause jewelry to be damaged during activities such as gardening.

Moh's Scale of Relative Hardness

1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase Feldspar
7. Quartz
8. Topaz
9. Corundum
10. Diamond
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