"Red diamonds are almost priceless — and almost impossible to obtain,” says one gem industry report. Each year the Argyle mine in Australia, the largest producer of fancy colored diamonds in the world, invites a select group of buyers to bid on its finest red and pink diamonds. From the mine's annual output of some 600 million stones, a mere 60 typically make it to this select offering — a "stunningly minute” number, as an Argyle officer notes.
The gems at this exclusive showing represent the best of the best, but even these diamonds are not, strictly speaking, red. They are graded as "vivid Purplish Pink,” "intense Purplish Red,” "fancy Brownish Red,” etc.
A natural diamond that is truly red is rare indeed. In 1987 the famous Hancock red diamond, weighing less than a carat, set an auction record by selling for $880,000, or $926,000 per carat.
Only a few other red diamonds are known to exist in the world. Experts say red diamonds would now sell for more than a million dollars per carat — should any appear on the market.
But red being the attraction that it is, and fashion being the market force that it is, red diamonds are in demand. For the supply: technology comes to the rescue.

The world's largest red diamond is known as the Red Shield, and weighs "only" 5.11 carats, compared with over 600 carats for the largest diamond of any kind. It would get anywhere near the list of the world's largest diamonds, yet it is famous for the fact that it is red, one of the rarest colours for diamonds.