The last time Sylas had seen something like this it was back when he used it to freeze time so that he wouldn't lose as much to the time dilation. But this item, while just as substantial if not more so, wasn't related to time at all.
Aetherstone Mines were extremely valuable, but also extremely difficult to actually mine. There was a great deal of caution that needed to be taken.
The problem was that the deeper you went, and the more valuable the Aetherstone, the more energy was concentrated and the more troublesome it would be to cut into such a thing.
It was the same concept as the formation of valuable stone back on pre-Summoning Earth. A great amount of pressure was applied on Aetherstone mines over a long period of time, and this pressure compressed the energy into more and more valuable states.
But it likewise made them more volatile.
