Phillip Ball:

Yet what if it were true that diamonds really can be manufactured? When GE revealed the discovery, the stock of the De Beers diamond cartel in South Africa, which dominated the global market, plummeted. It seemed like a rare and precious commodity was about to be supplanted by an artificial form that could be fabricated by the ton, mirroring a millennia-old concern about the devastating power of fakes. Concerns over the devaluation of gold currency led the Roman emperor Diocletian to ban alchemy in the third century, and worries about counterfeiting and debased coinage also lay behind the condemnations of the art by Pope John XXII in 1317 and of King Henry IV of England in 1403.
 This, though, was no alchemy: The GE diamonds were perfect chemical replicas of the real thing. Was it the end of a billion-dollar market?