What mineral was previously more expensive than gold and silver?

It was very, very difficult to get it at that time. People did not know modern booty. Naturally, you cannot easily give it up so hard. So the producers had to return the costs. Evaporation was a very difficult process in those days. The salt is hidden in this assignment. So it turned out that the price was simply fabulous. The salt tax also played a huge role in this “salt business”, that is, salt prices were high.