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.