The Six Kal Stones were forged from Aten's former body, before he died, he wanted a way to live forever and finally he found it, he assigned Phobos to create them and hide them until he could return immortal. The Kal Stones also had the ability to channel one element into the user, take for instance, Vulcan, the stones channeled Fire through him while changing into Vulcanic, you can only wield one element through them.