The Philosopher's Stone was a magical object. According to Morgaine Le Fay, the stone had incredible magical powers, most noticeably the power to manipulate time and reality itself, and able to materialize temporary illusions permanently.
According to Arthurian lore, the Philosopher's Stone was a gem from the hilt of Excalibur, the sword wielded by King Arthur. During Morgaine Le Fey's siege of Camelot, the wizard Merlin hid the Stone from her reach, knowing that if Le Fey ever possessed it, her powers would be increased to a point in which she would be unstoppable. The Philosopher's Stone was hidden in Merlin's Ark at Castle Branek, which was excavated shortly after World War II by archaeologists Henry Moss and Harv Hickman. Hickman discovered the Stone and kept it for himself. With it, he gained riches and became a magazine publisher. Years later, during Le Fey's pursuit in finding the Philosopher's Stone, she and members of the Justice League tracked down Hickman, who had the Stone displayed in his bedroom, though lost it after Wonder Woman fled with the Stone. After successfully retrieving the Stone, the League locked it away in the Watchtower only to be stolen by J'onn J'onzz, a martian who longed to see his long-gone family again as Le Fay promised him. Ultimately, J'onzz came to realize that the price was too high and destroyed the Philosopher's Stone before Le Fey's eyes.