Nenya, Ring of the Elves

Nenya, also known as the White Ring, the Ring of Adamant, and the Ring of Water, is one of the Rings of Power, specifically, one of the Three Rings of the Elves of Middle-earth.

Described as being made of mithril' and set with a "white stone" of Adamant, the ring is wielded by Galadriel of Lórien, and is not normally visible; while Frodo Baggins can see it by virtue of being a Ring-bearer himself,Sam Gamgee tells Galadriel he only "saw a star through your fingers."

Also check out the other 2 elven rings of power Vilya and Narya.