Large diamonds made from gas are the hardest yet

Since there is no mention of crystallography, one can assume these are cubic diamonds in which the extra annealing cycle simply reduces the defect density which could, however, also improve the hardness of natural diamond. What was the as formed hardness??? I wonder if they formed any hexagonal or rhombohedral phases.

Here are some other tidbits along similar lines. This form of graphite is quite interesting, it rivals the hardness of diamond yet has a significant improvement in fracture toughness. (it cracked the diamond anvil)