Crystal Skull of Charax
From The Griffin's Crier
The Lich Charax was the guardian of the former resting place of Necropolis after it was pulled into a pocket dimension creating the Fading Land of Necros. Stories say he crafted a skull from chalcedony and used it as his phylactery as he descended into demi-lichdom.
While it is said that the skull has the power to open a portal to the Fading Lands of Necros; the Ghostbane Scrolls of Ryda tell how a group of necromancers instead used skull to call forth a vast scourge of undead. It also tells how the Flan hero Telan defeated the necromancers and shattered the skull, scattering the fragments, placing them in remote locales that no one could ever hope to find.