Which is the hardest substance ? why is it so?

Diamond is regarded as the hardest known material in the world.But now scientists have calculated that a material called as lonsdaleite which is also called hexagonal diamond, since it’s made of carbon and is similar to diamond, is 58 percent stronger than diamond.
The scientists explain that the superior strength of lonsdaleite is due to the materials’ structural reaction to compression. Normal compressive pressures under indenters cause the materials to undergo a structural phase transformation into stronger structures, conserving volume by flipping their atomic bonds.Lonsdaleite have subtle differences in the directional arrangements of their bonds compared with diamond, which is responsible for their unique structural reaction.

Approved

Diamond no longer nature's hardest material

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 per cent harder than diamond.

Zicheng Pan at Shanghai Jiao Tong University in China and colleagues 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 first, wurtzite boron nitride has a similar structure to diamond, but is made up of different atoms.

The second, the mineral lonsdaleite, or hexagonal diamond is made from carbon atoms just like diamond, but they are arranged in a different shape.

Only small amounts of wurtzite boron nitride and lonsdaleite exist naturally or have been made in the lab, so until now no one had realised their superior strength. The simulation showed that wurtzide boron nitride would withstand 18 per cent more stress than diamond, and lonsdaleite 58 per cent more. If the results are confirmed with physical experiments, both materials would be far harder than any substance ever measured.

Doing those tests won't be easy, though. Because both are rare in nature, a way is needed to make enough of either of them to test the prediction.

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.