If someone were to ask to you to guess the most expensive substance on earth, you would probably reflexively answer "printer ink." Yeah, it's quite pricy, but nothing compared to some substances you don't think of because you can't afford them anyway. But what makes a substance expensive? First, there's supply and demand. If something is rare, like a red diamond, people are willing to pay more to have it. Or the expense could be calculated by how much we invested to get it. Samples brought back from outer space require millions to retrieve, and are irreplaceable. Or it could be that a substance is just so wonderfully useful, like a cure for cancer.
Science Focus has a list of the seven most expensive substances on earth, and the top two both combine all three reasons: they are rare, very difficult and expensive to manufacture, and highly coveted because of their usefulness. But you won't guess what they are until you read about them. -via Real Clear Science
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