The Tear of Oshtur is a medallion containing many magical properties, including the ability to repel magic on its holder. It also has the power to direct its holder anywhere he/she wish to go. The Tear was in the possession of Doctor Strange.
Strange later gave the Tear of Oshtur to Superman in his quest in saving Clea from Dormammu in the Dark Dimension, and as well enchanting the medallion to emit the same light as Earth's sun so that Superman's powers do not diminish in the Dark Dimension.[1]