Ithildín or moon-star was a mithril-celeb alloy invented by the Mîrdain of Eregion. Ithildin was only visible when reflecting moonlight and the right formula was recited.
| Boromir: "Is it not a strange fate that we should suffer so much fear and doubt for so small a thing? So small a thing!" - J. R. R. Tolkien, The Fellowship of the Ring II:10 |