Synthetic diamond "nanocrystalline" and "microcrystalline" diamond, respectively. Synthetic diamond is the hardest known material, where hardness is defined as resistance to indentation. The hardness of synthetic diamond depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the <nowiki>[</nowiki>111<nowiki>]</nowiki> direction (along the longest diagonal of the cubic diamond lattice). Nanocrystalline diamond produced through CVD diamond growth can have a hardness ranging from 30% to 75% of that of single crystal diamond, and the hardness can be controlled for specific applications. Some synthetic single-crystal diamonds and HPHT nanocrystalline diamonds (see hyperdiamond) are harder than any known
Centenary Diamond initial efforts were done by head rather than with a hand or saw so as not to heat or vibrate the diamond. After cutting and removing of cracked material over 154 days, the team was left with an egg-shaped gem of approximately . Thirteen different designs were presented to the De Beers board, with a strong recommendation for what became the eventual modified heart-shaped design. The shape was described as, "Effectively, the Centenary Diamond is shaped like a heart-shape, but it does not have a groove. The image the team had in mind was a shape which would adorn the