Soul Gem (Oblivion)

General Information
A Soul Gem is an object capable of storing the soul of a dead being. Soul gems come in various sizes: petty, lesser, common, greater, grand and black. The bigger the gem, the greater the soul that can be stored in it. These trapped souls can then later be used to recharge magical weapons or to create new enchantments.

To capture a soul, you must have an empty soul gem in your inventory. Cast the Soul Trap spell on the target, and slay it before the duration runs out. If done correctly, the soul will be trapped in the first appropriate soul gem available in your inventory. If no soul gem large enough for the class of soul is available, an error message will displayed and the spell will fail. Be warned that in the opposite event (there is no small enough stone available) a larger stone will be used instead, effectively wasting the larger gem, as soul gems are not reusable.

Special Soul Gems
Azura's Star is a reusable Soul Gem, obtained by completing Azura's task at the Shrine of Azura.

Black Soul Gems hold humanoid souls (Imperial, Argonian, Khajiit, etc, as well as Daedric kyn). All others, including Azura's Star, hold only the souls of creatures: animals, or the non-humanoid daedra found near or inside Gates of Oblivion. They are created by placing a Grand Soul Gem on one of four necromancer altars in Cyrodiil, then casting Soul Trap on the altar at the appropriate time. They can also be found rarely on necromancers.

Soul gem sizes
1: These creatures can be summoned using Conjuration spells.