Sup Veeky Forums, a while back my D&D group were exploring a tomb said to contain a fountain of blessed water when myself (the Cleric) and the party wizard were separated from the others and stumbled upon a small black and gold gem that detected as strongly necromantic. Lo and behold, a few sessions later when we finally got a chance to analyse this gem, Identify told us little save what we already suspected. The gem is akin to the gems used in a Trap the Soul spell. Yet, this is not all, as it contains innumerable souls. The DM told me that if I tried to count them, it would take me more than my mortal lifespan (which, as a human isn't huge, but still). What Identify didn't do, was give us any indication of how powerful the stone was, or how to use it in any way... something which only happens when used on either cursed items, or artifacts.
What should we do with the stone Veeky Forums? Should we return it to the Crypt like one of my Tribal Elders told us, or should we use it?
If we do use it, what are some creative uses for souls? We've already discussed using it to create magic items, and I thought about using it to substitute souls for material components of other spells. Any other ideas that you guys have?
System is D&D 3.5. The setting is relatively low-magic due to actual wizards, clerics, sorcerers, and druids being exceptionally rare and magic items being near-unique. Arcane magic is viewed as devilry in most of the world, to the extent that wizards are arrested, executed, lynched, or locked in their own towers by the lords of the land.
TL;DR - What are some cool uses for souls in a setting with rare, but extremely powerful, magic?