Black stone (Ritual of the Mahjarrat)

The Black stone or black prism is an object located in Zemouregal's fort in The North during the quest Ritual of the Mahjarrat. It is a magical item created from Obsidian which its owner, Zemouregal, created using materials he found in Karamja Volcano. According to Zemouregal in his Heart magic notes, it will give him the ability to have greater control over the undead hero Arrav's heart, making him less likely to resist Zemouregal's powers. During the quest, the player infiltrates the fort and destroys the stone, allowing Arrav to be swayed when he comes into contact with his heart.