J.R.R. Tolkien associates the mines of Moria with the fictional metal mithril.
Mithril is a rare, light, strong, and valuable metal found in Khazad-dûm beneath the Misty Mountains. The Dwarves mined it extensively, and its value became central to the wealth and fame of their underground kingdom. In Tolkien’s invented languages, the name is connected with the idea of “grey glitter.”
The metal appears in several important objects. Bilbo’s coat of mithril is given to Frodo, and its protection becomes significant during the journey. Aragorn’s sword Andúril is not made of mithril; that is a frequent mix-up. Mithril is also associated with the metal called true-silver in Tolkien’s wider descriptions.
Mining too deeply while seeking mithril led the Dwarves to awaken Durin’s Bane, the Balrog. After that disaster, Moria was abandoned. Tolkien later connected mithril with a rarer Elven substance in a posthumous account, but Moria remains its most famous mining site.