Nenya

In the fiction of J.R.R. Tolkien, Nenya, also named the Ring of Adamant and the Ring of Water, is one of the Rings of Power of the Elves of Middle-earth.

Nenya is described as being made of mithril and set with a "white stone", presumably a diamond (this is never stated explicitly, although the usage of the word "adamant", an old synonym, is strongly suggestive). The ring is wielded by Galadriel of Lorien, and not normally visible; while Frodo Baggins can see it by virtue of being a Ringbearer, Sam Gamgee tells Galadriel he only "saw a star through your fingers" (This appears in many editions as "finger" - which, sounds more magical, since it suggests that her finger has somehow become transparent - but the The Treason of Isengard, ch. 13, note 34, mentions it as an error.) Nenya was made by Celebrimbor and the Mírdain of Eregion.