The Mohs Scale.
Gemstones are ranked according to their Mohs hardness. Mohs hardness refers to a material’s ability to resist abrasion or scratching. Although a hard gem is not automatically tough or durable. It was devised by Friedrich Moh in 1812, the scale grades minerals on a scale from 1 (very soft) to 10 (very hard).
Remember the difference between the hardness of a diamond and that of a sapphire, is much greater than the scale suggests – diamond at (10) is about 4-5 times harder than sapphire (9), which is about 2 times harder than topaz (8). So it’s a guide – to know which stone is harder, but not by how much.
Mohs Scale of Hardness is as follows:
9 Ruby and Sapphire
8.5 Chrysoberyl, Synthetic Cubic Zirconia and Alexandrite
8 Beryl, Emerald, Aquamarine, Topaz, Spinel and Morganite
7.5 Garnet, Tourmaline and Iolite
7 Quartz, Amethyst, Citrine, Agate and Peridot
6.5 Zircon, Andradite, Zoisite, Tanzanite, Jade, Pyrite, Hematite and Kunzite
6 Feldspar, Scapolite, Glass, Rhodonite, Labradorite and Moonstone
5.5 Opal, Lapis Lazuli, Turquoise, Sphene and Diopside,
4 Fluorite, Rhodochrosite and Malachite
3 Calcite, A penny, Coral and Pearl
2.5 Silver, Gold, Amber and Serpentine
The Moh scale isn’t used as a test much, its the last resort as the stone has to be scratched and if so, it is done on the underside of the stone where it is less visible.