You've all heard the story about American settlers buying Manhattan for a handful of buttons. What is left out of the story is that those natives used shiny shells as money/jewelry and saw a lot of value in them, but had no concept of land ownership. This is no different than renting a house for gold or diamonds. One person sees some shiny rocks and the opportunity to live in a nice house. The other sees riches, while retaining ownership of the property.
Diamonds are worth a lot because DeBeers (sp?) convinced women that is was their best friend, and that a suitor was a jerk if he didn't spend a months salary on a ridiculously small rock. I've heard, but can't confirm, that there are places in Russia where these same rocks can be picked up off the ground. Diamonds are now so cheap to manufacture that we can buy grinding wheels made from them at Harbor Freight of all places. To keep the price up, jewelry companies have taken to microscopically enscribing serial codes on the little rocks dug up by child labor in Africa.
It is all worthless, and just a way for us to have a more efficient society than straight bartering allows. The opening paragraphs to "Hitchhiker's Guide to the Galaxy" is really appropriate here. When it all comes crashing down in a few years, the only thing that will really be worth anything is bullets. Even then, only if you have the means and will to use them.