Diamond no longer nature's hardest material - tech - 16 February 2009 - New Scientist
What is the hardest known substance? Turns out it's lonsdaleite, which is made from carbon atoms but arranged in a hexagonal fashion. It's not even the second hardest, that title falls to wurtzite boron nitride, which also has the benefit of being more stable than diamond at high temperatures.Diamond, in fact, comes third.