Oh oh oh...

Looks like you've stumbled upon the Jewel of Nir....
You know, the story about the human who was invited to Dwarven halls because he had saved the life of the Thane's eldest son...
The first non-dwarf allowed to see the mighty awe-inspiring forges burning with the heat of the everburning flame, modelled after the Soulforger's workshop. It was breathtaking, as were the marvelous works therein, but the thing which gaught Nir's eye was not something eleborated nor refined, although it was marvelous in its own: mithral, harder than steel but lightweight as leather.
Greed settled in Nir's heart. As he praised with foul intent the stout folk's craftmanship, after a year of his stay had gone by, he was to depart... But he had told the Thane's son of his fascination for their work, especially for that strange nigh-divine metal, a jewel -as he described it-.
Dwarven pride or dwarven gratefulness, probably both. At dawn, after the Thane himself was to say farwell to the saviour of his son, the son appeared with a exquisite sword held unsheathed... the ease with which it was wielded, the shine of the blade, Nir knew it, it undoubtedly was mithral. The son sheathed the sword and came beside Nir, whith the intent of giving a gift to this man of good who so enthralled was with dwarvencraft.
Here is where the story gets blurry and the songs of the bards are in discord. Some say Nir had been possessed, some say it was plain human greed, even others say it wasn't him but a transmuted duergar. The truth is that Nir rode into the night with a bloodied mithral blade, and the elderly Thane thrice cursed the human, and made sure he wouldn't ever drop the "Jewel".
When Nir encountered himself at a dwarven outpost at a later date he unwittingly unsheathed the sword, which misteriously was still wet with blood; the dwarves asked for explanations, but so fascinated he was with his "Jewel" that he described it's origin, always unfailingly praising the blade... They didn't take it kindly, some say he escaped the outpost blade in hand, unable to sheathe it, others say the dwarves killed one another for possession of the blade, all agree in that the
Jewel is cursed.
Or maybe it's just a random mithral cursed sword.
