The Philospher's Stone, also sometimes called "Lapis Philosophorum", is a powerful magical artifact and one of the many items in the DC universe.
It is the holy grail of western and spiritual alchemy. There are 3 theories as to the stone's function: an object that could turn inexpensive metals into gold, an elixir that makes mortal humans younger, or an item that could bring enlightenment to its owner and facilitate the completion of the owner's Great Work. The Stone was theorized as having transmutation properties by the 8th century Arab alchemist, Jabiribn Hayyan. He analyzed each element into 4 basic qualities: hotness (fire), coldness (ice), dryness (earth), and moistness (air). Each metal was a combination of these four; two interior and two exterior elements. Transmutation happened by rearranging these qualities. A dry red powder made from the Philosopher's Stone created an elixir that would mediate the process. The 16th century Swiss alchemist, Philippus Paracelsus believed it was an undiscovered element in which the four elements were derived from. An alchemist named Samael Aunweor believed it was a symbol of spiritual and religious tradition used to reject creative sexual energy and pursue spiritual edification.
It has later become the criminal weapon of both Doctor Alchemys, and in this capacity it has been used for a variety of evil uses. Apparently, this version of the Stone is essentially indestructible (as it reforms independently after each destruction) and at least partly magical in nature; it works by simply willing to transmute objects by holding it. Doctor Alchemy used it to usurp Power Girl's body by transferring his essence through the Stone, and was also able to use the Stone's magical applications to drain the knowledge of the magical Library of Alexandria stolen by the alchemist Megistus before compelling Power Girl to travel to the Fortress of Solitude to warp it in its entirety into red kryptonite with the stone's magics; before Wonder Woman threw it into the Sun, straight into Megistus' solar base. It would later play a pivotal role to thwart the alchemist's hopes of mutating all of humanity to protect it from the Final Crisis, when June Masters took it and used it to transmute the cosmic cloud the alchemist wanted to draw to Earth to common elements.
Appearances in other media
The Philospher's Stone appeared in the 2-part episode "A Knight of Shadows" of Justice League and it was a magical relic that is considered to be the most powerful object in the world.
According to Morgaine Le Fey, 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 away from her reach, knowing that if Le Fey ever possessed it, her powers would increase 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 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, the Martian Manhunter, who longed to see his long-gone family again and to return to his home planet of Mars as Le Fay promised. As Morgaine awaits J'onn and the Stone, she then transform all of the city of London into a massive medieval palace for Mordred as she promised her son that she will use the Stone's infinite magic to make all this transformation permanent before midnight on All Hallows' Eve (Halloween) and rule the world forever. While J'onn came to the castle and tried to give them the stone, Etrigan and the Justice League arrived in time to stop him as they entered a struggling but losing battle against Morgaine and Mordred. Ultimately, J'onzz came to realize the price was too high and crushed the Philosopher's Stone with his bare hand before Le Fey's eyes.