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
Diamond flaw scale the price down considerably. These diamond flaws are present on the surface of a stone and can occur naturally. However, these are more likely to be caused by the external environment when a diamond was being cut and polished. These are fine lines found on the surface of the diamond. They may have been present naturally or caused when a diamond was cut. While minor scratches can be removed through proper polishing, deep scratches can rarely be removed by treating the diamond. These are usually cut to remove blemishes or certain close to surface inclusions on diamonds. At times