Black Soul Gem (Oblivion)

Black soul gems function much the same as regular soul gems, with the exception of being used to trap Human souls instead. They are first found in Falcar's quarters in the Cheydinhal Recommendation quest, and they play a major part in the quest Necromancer's Moon, being the main focus of that mission. Later in the Mage's Guild quest "Ambush", the player and three other mages are sent to perform an assault on a Necromancer stronghold, Silorn, to find Falcar carrying a Colossal Black Soul Gem. To summon Vaernima at her shrine, the player must offer a black soul gem.

Creating
To create a Black Soul Gem, the player must take a Grand Soul Gem to an Altar at: Dark Fissure, Fort Istirius, Fort Linchal, and Wendelbek. At any of these locations, the player can create a Black Soul Gem, provided it's the day of the Revenant's Shade (occurs every 7 days starting on first day). An astral beam of light will fall of the Altar at night lighting it for all the world to find. The player must place a Grand Soul Gem in the Altar. Once a soul trap spell has been cast on the alter, it will be transformed into a Black Soul Gem.