Mithril is a fictional metal found in J. R. R. Tolkien's Middle-earth writings. It is described as resembling silver, but being stronger and lighter than steel. It was used to make armour, such as the helmets of the citadel guard of Minas Tirith, and ithildin alloy, used to decorate gateways with writing visible only by starlight or moonlight. Always extremely valuable, by the end of the Third Age it was beyond price, and only a few artefacts made of it remained in use.
Impenetrable armour occurs in Norse mythology in Hervarar saga ok Heiðreks, a story that Tolkien certainly knew and could have used for his mithril mail-coat. Mithril is the only invented mineral in his Middle-earth writings. Chemists note mithril's remarkable properties, strong and light like titanium, perhaps when made into alloys with elements such as titanium or nickel, and in its pure form malleable like gold.
The scholar Charles A. Huttar states that Tolkien treats mineral treasures as having the potential for both good and evil, recalling the association of mining and metalwork in John Milton's Paradise Lost with Satan. The scholar Paul Kocher interprets the Dwarves' intense secrecy around mithril as an expression of sexual frustration, given that they have very few dwarf-women.
The metal appears in many derivative fantasy works by later authors.