Black Soul Gems are a type of Soul Gem that can contain both black and white souls.
Soul Gems are used for harvesting the souls of non-sapient creatures and then binding them into the gem. This bound soul can then be used for enchanting weapons and armor, or other purposes of the arcane.
Black souls are those of sapient, humanoid beings such as Imperials, Argonians, and Dremora, while white souls are those of animals, certain lesser Daedra, and Giants. All black souls are of the Grand level. Since Hannibal Traven was appointed head of the Mages Guild, the practice of Necromancy has been banned, and along with it the use of Black Soul Gems. Two Black Soul Gems are the proof that Falcar has been secretly practicing Necromancy; however, these are "fake."
The Black Soul Gem is the largest Soul Gem, and can carry black or white of any category. When filled with the best applicable soul, their capacity utilized in enchanting is 1600, like the Grand Soul Gem.
To create one, take an empty Grand Soul Gem to an altar at Dark Fissure, Fort Istirus, Fort Linchal, or Wendelbek on the day of the Revenant Shade. This occurs every eight days starting on the first day of play. An astral beam of light will fall onto the altar at midnight. Once an empty Grand Soul Gem has been placed in the altar cast a Soul Trap spell on the altar; the soul gem inside will be transformed into a Black Soul Gem.
- There are two other versions of the Black Soul Gem. The first, 0003C7FC, is a quest-specific item used during the "Cheydinhal Recommendation" quest. It cannot be used to trap character souls, nor can it be used as an offering to Vaermina's Shrine. The second, 0001EC14, cannot be used and cannot be found in the game anywhere. The only way to acquire this one is through the console.