Diamonds are an endangered species, because they can now be manufactured. Very soon, "artifical" diamonds will be indistinguishable from natural ones. It is absurd for anyone to pay good money for any diamond. However, Gold may never be replicated. Alchemists have been trying for centuries, to no avail.
If they don't do any better job than they do with rubys and emeralds than manufacturing them won't make any difference. If you buy any of those stones you can tell the difference between them instantly.