But it needs a MacGuffin.
At any rate, at this stage it's a MacGuffin. Properly developed, it might not be. Certainly slapping a coat of paint on it and putting some detailing can cover up the fact. And it's caught between the tension that the plot might dictate some of its details, but then again, inventing details might help mold the plot. . . the essence of working out a plot is boxing yourself in. You just want to box yourself into a good location.
Ah, well, all I know now is that the MacGuffin is something magical that can, and will predicatably, cause a lot of trouble. In the future. Not now.
I might make it a ring and call it a tribute to The Lord of Rings. Or a gemstone, those are an old tradition too.