Also, Nenya, one of the Three Rings of Power, was described as the Ring of Adamant, once again the Dark Tower Barad-dûr is described as being a tower of adamant crowned with iron.
The Dark Tower Barad-dûr is described as being a tower of adamant crowned with iron. This was as the Ring of Adamant. This was once again. This was what Nenya was described. Nenya was one of the Three Rings of Power.