Actually, they're quite plentiful. Rubies are the gemstones that are truly rare. Yet men have been slipping diamond rings on women's fingers for more than a century, both sexes convinced that this expensive stone is the only real way to express true love. Turns out this tradition was spurred by nothing more than a savvy public relations campaign coupled with a big dose of corporate skullduggery [source: Kaplan].
It all began in 1880s South Africa, when Cecil Rhodes, head of De Beers Consolidated Mines, realized if he purchased as many diamond mines as he could, then restricted the supply of stones they produced, he could jack up prices. So he and his successors did just that, at one point controlling some 90 percent of the world's rough-diamond trade [source: Zoellner].
Along with this strategy, the company eventually enlisted the help of crack ad agency N.W. Ayer & Son, which created the "A Diamond Is Forever" campaign in 1914, considered by Advertising Age to be the most recognized and effective slogan of the 20th century. (It's still in use more than 100 years later) [sources: Kennedy and Kaplan]. The message? Diamonds are the one, true gift of love: No engagement is complete without one. The public eagerly bought into the campaign. Just as planned.