Heartstone

There are crystals, there are remnants of The First War that exist in this world and others. The very core of the elemental chaos itself, the hearts of the titans, left behind. These heart stones are the very basis, or, at least, shadows of the basis of what made the elements when creation came to be. The nature of these is that they cannot be taken out of the planes If they are brought beyond the plane themselves, "they generally shatter, and the few that can be brought across temporarily, the magics that contain them do weaken, and those that attempted to harness their power leave it to ruin, destroying all around them before it whirls itself into a frenzy of uncontrollable arcane mass and destroys everything nearby. These were many of the fools who ushered in the beginning of The Second War.
There are many heartstones, not a unique item
Some evidence seems to indicate that Heartstones are not forged, they existed. The remnants of the primordial Titans from the beginning of time, although Allura Vysoren claims that the heartstone used to exile Thordak WAS forged / created by the Arcana Pansophical
Possible that the "Heart of a Nymph", which is described as a crystal, was a Heart Stone? Would make an amount of sense... Also possibly why she inquired as to if Grog still had it when they go to the Feywild again?

The heartstone in Thordak is described as a pulsing heart of red glass. Osysa has a "heartglass" that allows her to "extend her vision". She also claims that using it "comes at a cost", which could possibly be similar / the same cost that Thordak is experiencing, except he can't turn it off since it's embedded in him. Her eyes are perpetually sky blue, and when she uses the heartglass it also turns the same sky blue Possibly indicative of it's elemental relation? Air? Also, Osysa claims that " Ioun herself" extends her vision via the heartglass. That seems a bit strange given that we have separate testimony that users of the heartstones, ones that brought them to the Material Plane, were "many of the fools who ushered in the beginning of The Second War."
Also, quote from Highbearer Vord , "The 'Dark gods' distanced themselves from the rest of the gods. They questioned the purpose of creation, and embraced the primordial chaos they once fought against". If the heartstones are the core of elemental chaos itself, and the users are blamed for The Second War, that seems very damning of Ioun's actions here in utilizing the heartstone. Osysa claims that they do a lot of good and that it's worth it, but that makes Ioun a hypocrite at the very least. Assuming, that is, that she was on the side of the divine gods during the Divergence. I am assuming that, since it appears that all of the "dark gods" were cast out, and Ioun is still around in some capacity at least.