We've been told over and over again that the world's hardest substance is diamond. On the Mohs scale of mineral hardness, it is at the top at 10.

However, it has recently been knocked off its pedestal by two substances called wurtzite boron nitride, 18% stronger than diamond and lonsdaleite, a whopping 58% tougher. Zicheng Pan and colleagues at Shanghai Jiao Tong University proved this in indentation tests.

Wurtzite boron nitride is structured like diamond but is not made from carbon atoms. Lonsdaleite is called the hexagonal diamond because while it consists of carbon like diamond, the atoms are arranged hexagonally. The reason why they are both so much harder than diamonds is due to the flexibility of their atomic bonds under stress.

They are both rare in nature. Wurtzite boron nitride is created during volcanic eruptions under very high temperature and pressure conditions. Lonsdaleite is formed from graphite found in meteorites after they land on Earth. Small amounts have also been produced in the lab but no one has yet come up with a way of making them in greater quantities. If they could, wurtzite boron nitride in particular will be ideal as a super abrasive for the tips of cutting and drilling tips. That's because it can endure higher temperatures than diamonds.

Diamond dealers can sigh with relief as these substances are not about to replace their gemstones. But from now on, if you ever hear someone say, "Diamonds are the hardest substance" you'd be able to say, "Not any more".

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Original Post by THE BEADING GEM
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