Locations:

Obsidian Enchantress tells you, "My specialty is creating magic gems and potions from certain pieces of crafted obsidian. If you have such an item, give it to me and I will return a useful and rare item."
Obsidian Enchanter tells you, "My specialty is creating magic adornments from certain pieces of crafted obsidian. If you have such an item, give it to me and I will return a useful and rare item."
Obsidian Enchanter tells you, "My specialty is creating magic orbs and potions from certain pieces of crafted obsidian. If you have such an item, give it to me and I will return a useful and rare item."