Heart of Earth

The Heart of Earth is one of the five fragments of the great Blackrock Obelisk of Pagan. It is Lithos' object of power. It appears in  Ultima VIII.

Description
When the Obelisk was shattered by the Guardian, the Heart of Earth landed in Stone Cove, where Lithos found it and stored it safely in the Catacombs, specifically the Pit of Death part that housed the Chapel of the Dead. It was there, where the Avatar found it in an ancient grave, and later used it to drain Lithos of his powers, destroying him in the process. It melted into the other fragments, reforming the Obelisk.

Trivia

 * Originally, removing the Heart triggered the undead invasion of Tenebrae but the event is removed from the released game. See Plot Cuts in Ultima VIII.