The Mohs Scale

Many customers who have made previous gemstone jewelry purchases are somewhat familiar with the Mohs scale. Developed in 1812 by the German mineralogist Friedrich Mohs, the Mohs scale provides a general idea of the durability of a gemstone by providing a hardness rating.

It is important to realize, however, that the Mohs scale is an ordinal scale. This means that there is not a proportionate level of hardness applied to each sequential rating. For example, topaz, corundum (sapphires and rubies), and diamond rate at an 8, a 9, and 10 on the Mohs scale, respectively. However, corundum is about twice as hard as topaz, but a diamond is almost four times as hard as corundum! This is further clarified by comparing how the mineral rates on a scale of absolute hardness, as measured by a sclerometer.

Below is a chart featuring some common gemstones with their corresponding Mohs scale rating and absolute hardness. Stones with a rating of less than an 8 on the Mohs scale are not necessarily recommended for everyday wear.

Mohs Scale Rating Absolute Hardness Gemstone
3 9
Pearl

Other gemstones include coral and malachite.

5 48
Opal

Other gemstones include turquoise and lapis lazuli.

6 72

Tanzanite

Peridot
Other gemstones include varieties of zircon.
7 100

Quartz

Garnet

Emerald
Other gemstones include colored varieties of quartz,
such as citrine and amethyst, as well as tourmaline
and aquamarine.
8 200
Blue topaz

Other gemstones include other varieties of topaz, alexandrite, and the diamond simulant cubic zirconia.

9 400

Corundum (rubies and sapphires)

10 1500
Diamond