Harder than diamond

An article in New Scientist reports that two naturally found minerals that have turned out to be 18% and 58% harder than diamond. “The gemstone lost its title of the ‘world's hardest material’ to man-made nanomaterials some time ago. Now a rare natural substance looks likely to leave them all far behind – at 58% harder than diamond.”

The simulations of stress-response run by Zicheng Pan at Shanghai Jiao Tong University and colleagues showed that wurtzite boron nitride was 18% tougher than diamond under stress. The second, mineral lonsdaleite, is 58% harder. The first, wurtzite boron nitride has a similar structure to diamond but is chemically different. The second, the mineral lonsdaleite, is hexagonal diamond made from carbon atoms but they are arranged in a different shape.

“Paradoxically, wurtzite boron nitride's hardness appears to come from the flexibility of the bonds between the atoms that make it up. When the material is stressed some bonds re-orientate themselves by about 90º to relieve the tension. Although diamond undergoes a similar process, something about the structure of wurtzite boron nitride makes it nearly 80% stronger after the process takes place, says study co-author Changfeng Chen at the University of Nevada, Las Vegas, an ability diamond does not have.”