"I can only tell you of the abattoir it had turned the temple I discovered it in into."

This sentence reads really awkwardly to me, and you might consider reworking it slightly. Otherwise, though, I like this one a lot.

Also referenced as: The Truthseeker, The Enchanter’s Gem
If you were to see the soulstone at a bazaar on any number of worlds, it would seem an innocuous bauble. A simple rose gem (heart cut –M), not especially brilliant, whose only remarkable feature is the size. It would seem easy to miss, except to those who know the touch of magic. Amid the flotsam and jetsam of countless trinkets, the soulstone draws those with power to it.

The stone allows its bearer to see to the soul of a thing and manipulate that soul, to draw forth its true potential... or snuff it out. It claims dominion over life and death, truth and lie. One could live forever with the stone's power, but it cannot stop one’s aging. It can command the dead to rise, but never offer true life. It can shield others from harm and end their lives with the same thought. The most subtle of all its power is to realize the absolute truth, to strip away falsehood and touch the soul of all things. It is this reason why it can draw forth the true potential of a soul, to remove that which stops one from achieving their highest potential. It is for that reason that beings of power have sought the stone for as far back as anyone can remember.

The exact origin of the soulstone is lost to the ages. The first mention I can find of the stone speaks of it as an item with considerable history, but of those events, I can find no trace. The tale was about the rise of a demonlord, already potent in his own right. However, bearing the stone gave him command of an undead army that made him nearly unstoppable.

Nearly.

One of his own acolytes turned against him just on the cusp of his victory. Using the stone, she bound their souls together and sealed him within herself. Without their patron, the cult was broken, the acolytes and priests fleeing before the assembled might meant to repel the undead army that fell useless upon the battlefield. The army of machines meant to defend the nation laid waste to the lesser demons that attempted to finish the demonlord's work.

One would think that would be the end of the story, but it doesn't truly end there. The gem’s power awakened something inside the young woman, a nascent spark flared to life because of its power. The next chapter of the journey takes something of an unexpected turn. The gem ended up in the hands of an accomplished healer on another world, presumably gifted stewardship of the stone by the young woman, though no mention of the exchange can be found. He began a grimoire studying the stone's capabilities, but as time wore on, the tome became his personal journal and when he died, it was passed to his daughter along with the stone. So it went for generations, until I arrived.

Only 2 of his descendents remained, a mother and daughter. The younger had inherited the burden, and though she was an accomplished healer like her ancestor, she did not wish to bear the responsibility given to her. She gave me both the stone and grimoire and seemed happy to be rid of the relic that had burnt out the potential of a once proud lineage.