The Philosopher's Stone is a precious rock carved by Elveron himself and imbued with his power to see into the future (or "sight beyond sight" as some call it).
Elveron originally created the stone to warn the one who touches it of what is to come and what must be done to prevent such an event. Should one place their palms upon it, the stone will immediately latch on to the person's hands and fill the person's head with images of the future and what will become of Aldrazar. Afterwords, the stone will explode and turn to dust.
Those that have touched it in the past however, never had the stone show them the images that are locked inside of it. It was later assumed that the stone chooses who must see the images, just as the Excalibur chose Arthur Pendragon.