Originally Posted by RalofTyr

The reason diamonds are so rare is that they are kept artifically scarce. The De Beers company, which is a cartel of families that own mines in South Africa (most of the families are British and De Beers was the original names of the owner of the farm the first diamond mine was found). They only sell the expected amount of marriages in the United States. So the price is always high. They also have a marketing campaign in the US (A diamond is forever) to get people interested in diamonds.