In the Superman folklore, he turns a lump of coal into a diamond by compressing it in his fist, cementing the idea in popular culture that diamonds are compressed coal. But in reality, while both diamonds and coal are both made of carbon, they are formed differently and at different locations underground. Coal and other fossil fuels are formed in the Earth’s crust (see the comments to an earlier post for some excellent information from readers about how fossil fuels form) but diamonds are created at much greater depths within the Earth’s mantle.
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