Black tourmaline core

The black tourmaline core is an item dropped by the Grotesque Guardians that can be found on the Slayer Tower's rooftop. They can be to upgrade the Bandos boots to create guardian boots.

When a player creates the guardian boots, a message in the chatbox will state ''The second you hold your tourmaline core by the Bandos boots, the core is absorbed rapidly. Perhaps there is some link between the metal in Bandos and tourmaline...''