ImageSoulstone.jpg 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.