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 orb that absorbed all the mana of other creatures, transferring it to him. The Avatar found out, a rock from the same material would destroy the orb. Gathering such a stone, the Avatar used it to destroy the orb and cripple Tyball's power, making his defeat much easier.