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
Recycled diamond Recycled diamond A recycled diamond is a diamond, which had a prior use and has re-entered the diamond supply chain. Diamonds in recent times have become good candidates for recycling, due to a number of reasons including their hardness and the gemstone being a finite and valuable resource. Diamonds are the hardest known naturally occurring substance and rate a 10 on the Mohs scale of mineral hardness. It has been speculated that the value of the market could be as high as $1 trillion US dollars. Traditionally, diamonds are considered a valuable commodity and large quantities of rough diamonds have