This papercraft is a Black Soul Gem, a special type of soul gem that unlike conventional ones, can only contain both black souls, based on the game The Elder Scrolls V: Dawnguard, the paper model is created by ZombieGrimm. The finished model measures about 6 inches.
Black souls are those of sentient, humanoid beings such as Imperials, Argonians, Khajiit and Dremora, while white souls are those of animals and certain lesser Daedra. All black souls are of the grand level. The main benefit of a black soul gem is that it can capture grand-level souls from humanoids, whereas those souls cannot normally be captured. Black soul gems can also absorb souls that are smaller than grand.
These sources tend to be plentiful and easier to kill, compared with common grand-level white soul sources, such as mammoths. 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. [Source: wikia]
You can download the papercraft model here: The Elder Scrolls V: Skyrim - Black Soul Gem Free Papercraft Download