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. 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. While the College of Winterhold doesn't forbid the practice of Necromancy, the use of Black Soul Gems is forbidden.

Summary
Generally regarded as unethical, Black Soul Gems are prohibited by The College of Winterhold. They can be found as random loot on Necromancers, Giants, Hagravens, Forsworn Briarhearts, and very rarely on Draugr. Magic Anomalies drop Black Soul Gems filled with Grand Souls. Black Soul Gems can also be found randomly in chests. They are available for purchase from Enthir, a mage of The College of Winterhold, as well as from Falion in Morthal. Each gem prices at about 300 Septims. Additionally, they can be obtained by mining Geode Veins, found only in Blackreach.

Where to Find

 * In Windhelm, Black Soul Gems can be found inside the hidden room in Hjerim after buying the Arcane Enchanter.
 * There is a Black Soul Gem in the Cracked Tusk Keep vault, to the right of the entrance, behind some iron bars.
 * There is also one in a half-buried pot in front of an altar in Geirmund's Hall, in the room just past Geirmund's corpse.
 * One can be found at the bottom of the pond at Steepfall Burrow, near the chest.
 * There is one in Broken Fang Cave, in the Master Vampire's chamber, and another at the Shrine of Talos.
 * Another one can be found atop Dead Crone Rock, on top of a platform in the tower (requires Unrelenting Force).
 * After completing Pieces of the Past, a Black Soul Gem respawns every week in the Shrine of Mehrunes Dagon. It is on the shelf at the very back of the shrine, to the right of the main chest.
 * It is also possible to get Black Soul Gems from Gulum-Ei at the end of Scoundrel's Folly, a Thieves Guild quest. The Dragonborn is given three random Soul Gems as a reward, any of which could be a Black Soul Gem.
 * There may be a filled Black Soul Gem in a chest in Serpent's Bluff Redoubt.
 * There is a filled one at the end of Shroud Hearth Depths. It is across a broken bridge, next to a Glass Greatsword in a small alcove that requires Whirlwind Sprint to reach.
 * In the Forsworn camp, just at the base of Bard's Leap Summit, there is a chest inside a tent. Inside is a Black Soul Gem.
 * Just a note, the College of Winterhold prohibits the use of Black Soul Gems, so you won't be finding any there. The only exception is Enthir, mage in the College of Winterhold, who will have 1-2 Black Soul Gems for sale every 48 hours.