Black Soul Gem (Skyrim)

Black Soul Gems are a special type of Soul Gem that, unlike conventional ones, can contain both black and white souls.

Description
Black souls are those of sentient, humanoid beings such as Imperials, Argonians, and Dremora, while white souls are those of animals and certain lesser Daedra. All black souls are of the Grand level. Nelacar can transform the star of Daedric Prince Azura, into a black soul gem with unlimited uses.

This artifact is known as the "Black Star". After a black soul gem is used for enchanting, the soul that was inside it goes to the Soul Cairn.

Use
Souls snared in Black Soul Gems can be of any type, although, unlike standard soul gems, they can encapsulate the souls of humanoids. There are many methods by which souls are trapped in Black Soul Gems, the most conventional method being the Soul Trap Conjuration spell. The perk "Soul Stealer" allows Bound weapons to soul trap targets, and an enchantment serving the same function can be added to ordinary weapons. They can also be used to create items at the Atronach Forge.