Fool’s gold is a good source of the real stuff

FOOL’S GOLD—pyrite, to give its proper name—may once have disappointed prospectors looking for nuggets. But modern miners have learned to love it, because inside its crystal lattice of iron and sulphur there is often actual gold to be found.It is never much—at most a few tenths of a percent. And extracting it is hard work which involves grinding and heating the mineral, and then treating it with sodium cyanide, which is extremely toxic. But that can be worthwhile. Some 5-10% of the world’s gold production derives from pyrite. And this is likely to increase. According to estimates by McKinsey, a consultancy, 24% of the world’s gold reserves are “refractory”—meaning the gold must be yanked from the clutches of some mineral, in most cases pyrite.