Dark Geode of Brin Balo

Under the roots of the Bundir Balo, the northern chain of mountains in Dark Geode of Brin Balo, far nearer the heads of illithid than feet of dwarves, a rich river flows. Through stone it cuts and in caverns it swells, the multitudinous stony waters of the Dark Vein. It runs down and down, growing more evil and more potent the deeper it falls. There's a sort of falls that empties from one earthen stomach to another, and the palpable darkness belches out from the vastness into which it descends. The darkness reaches down and grabs hold onto the core of the world, it is said, and there it tries to corrupt it and break down further into the Abyss, its true home.
This substance first came unto the dwarves in the Age of Reckoning, that mysterious Age. Here in the northern mountains, the outcast dwarves of Mil Bazon, ones that called themselves Bundir, crowded together. They were an evil lot and ruthless and chaotic and they worshipped dark gods like Abbathor, Bane and Beshaba, and more. Dark temples were raised on peaks to form the Clouded Peaks of Bundir Balo.
The wicked gods, granting them boons, blighted the land so nothing wholesome grows there. Two hundred thousand acres of black and oozing stone captures the pure snow that blows in that region. But alas, the snow turns gray and so garners the name "gray slopes" because of this. But it is under the gray slopes that the malevolent treasure lies.
Under the slopes the dark river flows, the evil seeping through the mountain like sewage and settling onto rocks that absorbed it, thirsty for sustenance. These rocks accepted the evil given to them and gave it to their neighboring stones until a million feet of the stuff stretches from the deepest darkness past the Underdark and straight to the core, finding its way back home.
These unique rocks hold the evil inside them, true, but that evil can be suppressed and forged. And that is exactly as the Brundir did. They fashioned dark stone axe heads, pickaxes, arrows, mauls, shields, armor. The heaviness fatigued them little, being granted strength from their dark tidings. They wielded these unholy machinations unto themselves and threw them at passersby, inflicting pains beyond the physical. They abhor all magic that is not from these stones, and no magic but magic from the stones is allowed on these peaks. No divinity dare grant their power to those who willingly go there, even to convert or kill. There is no known greater depravity than these barbarians and their own lives. They can be likened to skinwalkers from Hellia, but even they have some purpose albeit unknown to all others, and they stay secluded in their dark forests, festering and overrunning it like the vermin they are.
The Dark Geode, as it is known to us outside of the Gray Slopes, does have its uses. I can do a plethora of magical tasks, if harnessed correctly, and has been the subject of study by elven magicians for several generations of that kind. Much more can be learned, however, if one has ties to evil beings or is an exceptionally evil person themselves. It is said the stone speaks or sings to them, a mellifluous song that rings in the ears until it is all they hear. It beckons them and calls them, turning them into the zombied shells of themselves. Wights, ghouls, ghasts, zombies, and now gray bundirs. No divine or natural magic can heal one this far gone.
Naturally, research is carried out in groups with several scholars studying for about a week then taking a break for about three and repeating the cycle. This, so far, seems the most effective way to stay sane amidst all the darkness that seeps from the geodes.
The "geodes" themselves resemble actual geodes but with a viscous, black-and-purple substance that oozes out once broken open. Scholars have likened it to an egg or a coconut from Samba Ka. Once drained, the insides are of a dark, crystalline stone that can be forged with enough heat. A captured Bundir said that blood works better than water in the smelting process. The weapon forged will hold its shape and sharpness unless struck against stone or the like. But even still the dulling is considerably less than that of steel. The properties the weapon has, however, are just as intriguing as the stone itself. Any weapon formed with this can be used as a catalyst for spells, and can even store a spell for a limited time, though the cast will lose the ability to cast that spell unless with the weapon. This, along with their evil inclination, has led to many Bundirs being warlocks serving their dark gods. Eldritch blast is a favorite among them, though other spells, like dark fireball, have been known to be used.
There exists no real market for the things. They are too difficult to come by, too strenuous to handle, and too expensive to maintain to be any bit profitable. Still, shady dealers in the cities of Hlee, or Iron Quay, or allegedly in Yym, seek out these treasures for the immense power they hold. Indeed, many a greedy brigand who wishes for power finds a dark weapon to enact their malicious decrees.
These weapons cannot be destroyed as far as scholars know. There is a vault in each capital that contains the retrieved weapons. No one dares steal them, for they begin to corrupt the moment they are wielded. The furthest one has come to destroying one is a half-elf scholar studying in Mirdrinda at the mage's college there, The Lourimin. She managed to extract the darkness through fierce smelting, but the whole weapon exploded, cutting her. The darkness seeped in and she was poisoned.
The dark geode, while providing many interesting implications, is ultimately something to be ignored and repressed. No good has ever come from letting evil have free reign. Soon, there will need to be an eradication of Bundirs in Bundir Balo, but none have been born, are born, or probably will be born that are strong and brave enough to take on even on family in the accursed lands of the Gray Slopes.