> diamonds have societal utility because tons of people like them sounds like they have a subjective value   > of course you can sell a bar of gold for 2 cents you have no way of knowing the difference in labour between mining and smelting gold into a bar and mining, smelting and minting copper tin and zinc into a 2c coin.  you could also trade a bar of gold for a gallon of water, most people wouldn't, not because they know the amount of labour that has gone into the bar is greater than the gallon of water, an individual has no way to know said information.  they wouldn't because for most, the subjective value of gold is greater than that of water, but a person dying of thirst may place a different subjective value on the water than the gold, so their own personal value calculation may be different.
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