Mithril

Mithril was a precious silvery metal, stronger than steel but much lighter in weight, which was mined by the Dwarves in the mines of Khazad-dûm and could be beaten and polished without being weakened or tarnished. Mithril, also known as silver-steel and Moria-silver, was admired and treasured by all the races. The Men called it "true-silver" while the Dwarves, who loved it above all things, had their own, secret name for it.