Orb Rock

The Orb Rock is a very important item appearing in Ultima Underworld I.

Description
Tyball had erected a magic-free zone in the seventh level of the Abyss, having created a magical orb that absorbed all the mana of other creatures, transferring it to him to use as he pleased. The Avatar found out, a rock from the same material that the orb was made of would destroy the orb for good. Gathering such a stone from the original mines, the Avatar used it to destroy the orb and cripple Tyball's power, making his defeat much easier.