Soulstone

The Soulstone was a large crystal owned by Roper Klacks and kept in his laboratory. Several groups of soldiers were sent against him to force him to free the winds he had stolen, but Klacks captured them, took their souls, and trapped them in solid stone. He then put the souls he had taken into a magical crystal, called the Soulstone. He drew power from it, which may be why Klacks had greater magical power than the average Alchemist - Lorhan says that without the Guardian, the natural order has been upset, allowing such things to happen.

When April shattered the Soulstone using the Magic Binding Potion and then the Explosive Potion, it released the souls of the people Klacks had caught, including Lorhan's, and also broke the spell that kept the prisoners trapped in stone.

Dreamfall Chapters

In Dreamfall Chapters, the Soulstone—or soul-stone—is revealed to be a much more significant item than it initially seemed. Originally possessed by Klack’s master, the Yaga, it was allegedly stolen from them by Lux, so that the Dreamer could dream the world into existence. The soul-stone was later stolen by Klacks, who kept possession of it until his defeat and capture. Part of the stone was later retrieved by the Yaga, who fed on its energies until Zoë Castillo visited their realm and obtained it from them. Zoë returned the stone, now containing the Yaga’s essence, to Lux, who uses it to join Lux's own essence with Zoë’s, granting her Lux's powers and responsibilities.

Another fragment of the stone, meanwhile, was retrieved by the Prophet, who after freeing Klacks from his prison returned it to the warlock, along with instructions: Klacks would take the stone, now containing the Undreaming, into himself, and safeguard it. This stone fragment remained inside Klacks until Kian Alvane, using the Silver Spear of Gorimon pierced both the Warlock and the stone, shattering it and causing the Undreaming to escape and return to his original vessel, the Prophet.