Mithril

Mithril is a fictional metal found in the writings of J. R. R. Tolkien, being present in his Middle-earth, and also appearing in many other works of derivative fantasy. It is described as resembling silver but being stronger and lighter than steel. The author first wrote of it in The Lord of the Rings, and it is retrospectively mentioned in the third, revised edition of The Hobbit in 1966. In the first 1937 edition, the mail shirt given to Bilbo Baggins is described as being made of "silvered steel".

In The Lord of the Rings, Tolkien wrote that mithril is found only in the mines of Moria beneath the Misty Mountains, where it was mined by the Dwarves. Unfinished Tales alleges that it is also found in Númenor.

The name mithril comes from two words in Tolkien's fictional language of Sindarin—mith, meaning "grey" or "mist", and ril meaning "glitter".

Within the text, the wizard Gandalf explained mithril to others while passing through Khazad-dûm:

The Noldor of Eregion made an alloy out of it called ithildin ("star moon"), which was used to decorate gateways, portals and pathways. It was visible only by starlight or moonlight. The West Gate of Moria bore inlaid ithildin designs and runes. It is implied at one point that the "moon-letters" featured in The Hobbit were also composed of ithildin.

...
Wikipedia