Book of Shadows: Velsharoon's Soul Prison

This spell snatches the soul of a humanoid as it dies and traps it in a Emerald The imprisoned soul remains inside the gemstone until the spell is dispelled or the Emerald is destroyed. Before the actual casting of Velsharoon sol prison, you must procure a Emerald of at least 100 gp value for every Hit Die possessed by the creature to be trapped.

If the gem is not valuable enough, it shatters when the entrapment is attempted. (While creatures have no concept of level or Hit Dice as such, the value of the gem needed to trap an individual can be researched. Remember that this value can change over time as creatures gain more Hit Dice.)

The soul of the trapped creature appears as a screaming shadow of its former self, which appears in emerald.