What makes the diamond the hardest mineral

research : Diamond is not the hardest material

Theoretical models of a Chinese-American research team now show that pure wurtzite boronide is even 18 percent harder than diamond - when it comes under pressure and changes its crystal structure in the process. According to the calculations, the mineral Lonsdaleit is 58 percent harder than diamond, writes the team led by Zicheng Pan and Hong Sun in the journal "Physical Review Letters".

However, the new world record will only apply if the material can confirm these predictions in a practical test. The materials would be interesting for a wide range of applications, as they can withstand more heat than diamonds: for example as coatings for drilling and cutting tools or for spaceships.

In nature, the two materials occur only in small quantities, which are insufficient to test the theory, let alone to be used as a diamond substitute. Wurtzite boronide mainly contains zinc, sulfur and boron and forms under the extreme pressure and temperature conditions of volcanic eruptions. Like diamond, Lonsdaleit consists of carbon atoms, which, however, have a different geometric arrangement. The mineral is only produced under very high pressure: it is found after meteorite impacts, for example in the Siberian Tunguska crater or in the southern German Ries crater. The researchers hope that they will soon be able to use new production methods to produce significant quantities of the minerals and test their calculations. wsa

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