<blockquote>The diamond-holding public, which includes people who inherit diamonds, had to remain convinced that diamonds retained their monetary value. If it saw price fluctuations in the diamond market and attempted to dispose of diamonds to take advantage of changing prices, the retail market would become chaotic. It was therefore essential that De Beers maintain at least the illusion of price stability.</blockquote>
via <a href="http://www.theatlantic.com/magazine/archive/1982/02/have-you-ever-tried-to-sell-a-diamond/304575/4/">Have You Ever Tried to Sell a Diamond? - Edward Jay Epstein - The Atlantic</a>.