Diamonds can be produced in a lab. Unlike cubic zirconoia, these diamonds are molecularly identical to naturally occuring diamonds (and rival natural diamonds for clarity.
Now the diamond associations are asking the FTC that such diamonds be referred to as synthetic diamonds and not cultured diamonds. Cultured diamond creators argue that their process is analogous to that used for creating cultured pearls, in that the gem is created not by ‘synthesizing’ but by reproducing natural processes (WSJ reg req).