The emerald gem given to Aragorn by Galadriel. It's history is uncertain, with some tales saying it was made in Gondolin, taken into the West and returned by Gandalf, and others saying it was a replacement for an earlier stone by the same name. However, it was from this jewel that Aragorn took the name under which he ruled the Reunited Kingdom.
The jewel was able to augment healing powers, and make things appear as they
would have been had Morgoth and Sauron not corrupted the world.
The Unfinished Tales