The Magic Rock (Quest)

This quest involves locating a Heavenly Stone. It is initiated by Griswold after visiting level four. The stone itself is on a pedestal somewhere in level five. Taking it to Griswold results in the completion of the quest, and the Empyrean Band (a unique ring) from Griswold as a prize.

Diablo III
This quest returns in The Darkening of Tristram event as a standard interactable object. Found on Labyrinth Level 5, the player can find a medium sized crystal formation. Accessing the curio will result in a pile of Gems and the Empyrean Band.