Diamond Hardness vs. Toughness

Posted on December 20 2016

I thought diamonds are indestructible.  How did mine chip?

Diamonds are the hardest known natural material, but not the toughest. In everyday speech the words hard and tough are used interchangeable, but in gemology they have specific and separate meanings. Hardness is a material’s ability to resist scratches and toughness is a material’s ability to resist breakage, chipping, or cracking from physical force. The difference of terminology can be illustrated by comparing a relatively hard everyday item like china which is not tough at all, to a tough material like leather which is not hard. A china plate will chip or even break fairly easily if dropped but is hard enough to resist scratches by steel forks and knives. Conversely, leather boots will scratch easily with even a soft fingernail, but are tough enough to resist tearing or breaking. 

Even though a diamond is the hardest natural substance known, it is not the toughest, jade is. Diamonds have a grain that is visible under a microscope and are subject to break at this point. Diamond cutters are trained to find these cleavage directions and break off pieces along precise angles based on the crystal structures of a diamond. An extremely hard blow to the girdle, or any susceptible angle, may cause a diamond to chip. You can keep your diamond intact for a lifetime by having it set in a relatively protective setting, and remaining conscious of it when it’s on your finger.

All of the stones used to simulate diamonds are both less hard and less tough and will scratch or break more easily than a diamond. A diamond’s durability and ability to resist scratching is part of what gives them their eternal beauty.

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