Diamond will always be a woman’s best friend but the gemstone is no longer the “world’s hardest material”, according to scientists. Instead, a rare natural substance, called lonsdaleite, which is made from carbon atoms just like diamond, has emerged as 58% harder than the gemstone, according to a report in the New Scientist. An international team, led by Zicheng Pan at Shanghai Jiao Tong University, simulated how atoms in two substances believed to have promise as very hard materials would respond to the stress of a finely tipped probe pushing down on them. The simulation revealed that the first one, wurtzite boron nitride, withstood 18% more stress than diamond, while the second, the mineral lonsdaleite, 58% more.
Rare mineral lonsdaleite is sometimes formed when meteorites containing graphite hit Earth, while wurtzite boron nitride is formed during volcanic eruptions that produce very high temperatures and pressures. If confirmed, however, wurtzite boron nitride may turn out most useful of the two, because it is stable in oxygen at higher temperatures than diamond. And, according to the scientists, this makes it ideal to place on the tips of cutting and drilling tools operating at high temperatures, or as corrosion resistant films on the surface of a space vehicle, for example.
Paradoxically, wurtzite boron nitride’s hardness appears to come from the flexibility of the bonds between the atoms that make it up. When it’s stressed some bonds tend to re-orientate themselves by about 90º to relieve the tension. “Although diamond undergoes a similar process,
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