Question

is diamond hardest substances or not ?

Answer 1

Hope this helps you...
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It is recently proven that it is not true . Diamond is one of the hardest substance . Diamond is the hardest naturally occurring substance found on Earth. But it is not the hardest substance. Wurtzite boron nitride (synthetic) and lonsdaleite (which comes from meteorites) are both harder..

Answer 2

Naturally occurring hardest substance is Diamond.

Artificially made compound :  Wurtzite Boron Nitride... Made of different elements.. is the hardest substance on EArth.