Have You Ever Tried to Sell a Diamond? “In the 1971 De Beers annual report, Harry Oppenheimer explained the unique situation of diamonds in the following terms”:
A degree of control is necessary for the well-being of the industry, not because production is excessive or demand is falling, but simply because wide fluctuations in price, which have, rightly or wrongly, been accepted as normal in the case of most raw materials, would be destructive of public confidence in the case of a pure luxury such as gem diamonds, of which large stocks are held in the form of jewelry by the general public.
If normal people started selling their diamonds on the open market, the De Beers cartel would lose much of its monopoly power.