The Rainbow Mines of Carapithia IX
Discovery One day, a peasant was walking around and saw something purple sticking out of the ground. This (naturally) confused him, and he dug the thingamajig out. It turned out, it was a purple metal. He took it to his king, who ordered a total excavation of the site.
Use The king decided that only his elite magic knights could use the stuff, because there wasn't that much of it. This angered the king's advisor.