Mohs Scale – Gem and Mineral Hardness

Diamonds are known for being one of the hardest substances on earth. A diamond is so hard it ranks as a 10 on the Mohs scale–the highest level of hardness. But what is the Mohs scale?

The Mohs scale (pronounced MOZE) rates the hardness of gems and minerals. The hardness of a stone indicates the stone’s resistance to scratching or how the surface of the gem will respond to contact with a sharp point. This differs from a gem’s toughness, which is defined by how well a gem can survive an impact or resist breaking, chipping or cracking.

Introduced in 1822, the scale originated when Friedrich Mohs chose ten minerals and assigned numbers to them based on the relative ease or difficulty with which one can be scratched by another. His studies resulted in the scale below, which is still used today.

When looking at the Mohs scale, it is important to remember that the difference in hardness between minerals, or the hardness numbers, is not actually equal, even though the minerals look to be equally spaced. The diamond is only one number away from the Corundum mineral (which includes rubies and sapphires), however it is many times harder then the gems in the Corundum family.

The Mohs scale helps to identify what makes a gem durable. The more durable a gem is, the more suitable it is for use in frequently worn jewelry.


/* OnlineOpinion v5.9.0 Released: 11/17/2014. Compiled 11/17/2014 01:01:01 PM -0600 Branch: master 7cffc7b9a0b11594d56b71ca0cb042d9b0fc24f5 Components: Full UMD: disabled The following code is Copyright 1998-2014 Opinionlab, Inc. All rights reserved. Unauthorized use is prohibited. This product and other products of OpinionLab, Inc. are protected by U.S. Patent No. 6606581, 6421724, 6785717 B1 and other patents pending. Resource added 8/6/2015, */