Wow, diamonds suck:
"Surprisingly, diamonds are not rare, whatsoever! This might come as a shock to a person who has just paid 1,000 dollars for a one-carat stone, but there are enough diamonds in the world to give every man, woman, and child in America a cupful. Although they have the best reputation, diamonds are not the most expensive gemstone, either. A top-quality ruby would be double the expense of a diamond of the same carat. A diamond’s expense comes from a human-imposed drought rather than a true drought. The whole theory of supply and demand plays very nicely here into the hands of the diamond-governing corporations!
What is rare, however, is a good diamond. This next part might be bad news for you diamond-lovers out there. If we define a good diamond in general terms as one that has a large carat, is perfectly white, that has no fissures or cracks or clouds, has all of its potential brilliance, and will appreciate over time, less than 25 out of 1000 diamonds sold in the US would be good diamonds. The average person in the US pays twice what they should for their engagement ring, and the average diamond has been laser-drilled, is tinted yellow, and has cracks, breaks or carbon that you can see with your own eyes."
http://www.belgianexperts.com/diamonds.php