An employee holding up the molecular structure model of a diamond in the De Beers Element Six laboratory in Didcot, Britain. About 360,000 carats of man-made gems were produced last year, compared with 126 million carats of natural diamonds.

Because the man-made gems are nearly indistinguishable from those formed naturally, some sellers have tried to pass off synthetic types as ones that have been mined. At the De Beers lab, a team is developing machines for diamond buyers to distinguish synthetic stones being peddled as the real thing.