[TeMPOraL]

Of course it's not - but right now the value does not follow the real supply and demand curve, but is fixed by DeBeers, et al. We have lots and lots of diamonds, and if not for a clever decades long marketing campaign, they would be mostly worthless. Going to space to get more diamonds (which we don't need, because we already have too many of them) would be a colossal waste of resources.

[stephengillie]

This exactly. DeBeers changed the way Americans value diamonds, adjusting the demand curve upwards, so Americans expect to pay more money for diamonds.