What Rare Earths Are Locked in Your Cell Phone?
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Also, it's fun to take things apart.
Gold leaf is incredibly thin.
Why?
More seriously: permitting and infrastructure. Once you've spent a couple of years convincing people that you're not going to fill the water table with arsenic and you should be allowed to start building, you then realise that the mine is in the middle of nowhere and roads, railways, worker housing, electricity and water supplies all need to be provided.