Black Soul Gem (Oblivion)

Black Soul Gems are a special type of Soul Gem that can contain humanoid souls (Imperial, Argonian, Khajiit, etc. - including Dremora). All other soul gems, including Azura's Star, hold only the souls of creatures (animals, or the non-humanoid daedra found near or inside Gates of Oblivion). Black Soul Gems filled with a humanoid soul are just as powerful as Grand Soul Gems filled with a Grand soul. These items are considered evil, as they are evidence of wrongdoing in the quest Cheydinhal Recommendation. Since Hannibal Traven was appointed head of the Mages Guild the practice of Necromancy has been banned along with the use of Black Soul Gems.

Black Soul Gems can also be found on random necromancers or in chests (although this is rare).

These can easily be filled at low levels by entering the arena and casting soul trap on your opponent, this isn't counted as murder so you can get free souls. If you wish you could just kill a random npc.

Creating
Bob at Whiterun and Mia the prostitute Solitude Create these. Ask Bob at 12:00 am in the middle of Whiterun, he'll tell you that he's a Necromancer. Kill him and he has five on his corpse. Sleep with Mia and when you wake up she'll be dead. Loot her and she has ten Black soul gems and a Grand soul gem.

Black Soul Gems in Skyrim
Black Soul Gems trap humanoids within them, as opposed to standard Soul Gems (including Azura's Star), which house only white souls, or the souls of animals. Generally regarded as unethical, Black Soul Gems are prohibited by The College of Winterhold.

Locations of black soul gems

 * Black Soul Gems are available for purchase from Enthir, a mage of the college. Each Gem prices at about 1300 Septims.
 * Black Soul Gems can be found as random loot on Necromages, Giants, Hagravens, and very rarely on Draugrs. Magic Anomalies drop Black Soul Gems filled with Grand souls.
 * Empty and filled Black Soul Gems can also be found randomly in chests.
 * Black Soul Gems can also be found by mining Geode Veins. Blackreach is a good place to find these veins.
 * They can also be found inside the hidden room in Hjerim after buying the enchanting altar in Windhelm.
 * There is also one in the Cracked Tusk Keep's vault on the right hand side behind some iron bars as you walk in.
 * Another can be found laying in a half-buried pot in front of an alter in Geirmund's Hall, in the room just past Geirmund's corpse.


 * Can also be bought from Falion in Morthal.
 * One can be found at the bottom of the pond at Steepfall Burrow near the chest.
 * One can be found in Broken Fang Cave, in the Master Vampire's chamber.