In some locations on the Negative Energy Plane, the collapsing intensity of the plane was so great that the negative energy folded in on itself, stabilizing into solid chunks of utterly black matter. These were known as voidstones.
Completely black and featureless, a voidstone was nearly unmeasurable by any known means. Rough estimates of size could be made by the black hole it formed in any region of illumination.
There is speculation that voidstones were the basis for the creation of spheres of annihilation, and even natives of the Negative Energy Plane are not immune to their effects.
Voidstones may be of any size, ranging from inches across to dozens of feet.