Adamantine
Adamantine is one of several magical metals that have appeared in Dungeons & Dragons and, alongside Mithril, is one of the most iconic. Characterized by its jet-black coloration, adamantine is known for being super-durable; weapons made of the stuff can cut or smash through just about anything, whilst armor & shields made from it are virtually unbreakable.
The metal takes its name from a legendary ultra-durable metal in Greco-Roman mythology.