A substance with extraordinary properties, created from mithril. It was only visible in starlight or moonlight, and even then would only appear when brought to life by one who knew the appropriate invocation. It was used, for example, to trace the secret characters and images on the West-gate of Moria.

'Starmoon' is an approximately literal translation of the Elvish word ithildin (where ithil means 'moon', and 'din' means 'small, faint star'). The translation, however, loses some of the subtlety of the original name, because the root-word behind Elvish din can also refer to faint silver beams, and glinting, sparkling light, and these shades of meaning also clearly have a bearing on the name chosen for this magical material.