The Philosopher's Stone was an alchemical substance that could turn base metals into gold or silver. The stone could come in two varieties, white and red. The white stone was used to turn metals into silver, whereas the red could turn the metals into gold. It was also capable of creating the Panacea.
Giovanni Borgia accidentally discovered the formula for the Philosopher's Stone when he read the pages of the mystical Book of Abraham, one of the journals of Nicolas Flamel. After Giovanni wrote it down, Bombastus used the notes to create the substance.