Schemes of the Lich King
Soul Gems are magic gems that have wild, unusual properties. Soul Gems do very little on their own but when placed in a Socketed Items they can take on the property that the Soul Gem was created for. Effects can range from extra damage to an attack, turning the user invisible, at will, or having a target burst into flames. Empty Soul Gems are especially sought after as the owner can put in any magics they want, assuming they know how to do so.