Obsidian amulet

Obsidian amulet is an item used only in Creature of Fenkenstrain quest. It is found upstairs in Fenkenstrain's Castle. There's a bookcase in the east room. Search it for Handy Maggot Avoidance Techniques book, and you find it. Obsidian amulet forms a Star amulet when used with Marble amulet.