 It is implied at one point that the "moon-letters" featured in "The Hobbit" were also composed of "ithildin".In Tolkien's Middle-earth, mithril is extremely rare by the end of the Third Age, as it was now found only in Khazad-dûm.Once the Balrog destroyed Khazad-dûm, the kingdom of the Dwarves in Moria, the only source of new mithril ore was cut off.