"Well...couldn't hurt to ask, right? I hadn't considered it as technology. I was thinking there might be more like...some kind of branch off of whatever natural energy lies within the core of this planet. Instead of heating up underground springs, it crystalized within the walls. Iiii am not a geology expert though so this is all theorizing, of course."

Donnie frowned thoughtfully as he worked, although clearly distracted by the thought Tony placed there for him then. The key to that still seemed to be reliant upon figuring out just how the crystals were charged.

"I tried to see if I could rig a way to recharge the crystals that were mined. Unrefined, they won't recharge save when they're brought back to the caverns. Some kind of energy resonance or something- same as how powers are amplified I guess. I thought maybe I could make some sort of looping configuration but I think I'm going to need something that actually gives off its own energy to be able to do that."

He paused, looking almost sheepish at Tony's question, scratching the back of his head. "Er... Well it was at the back of my mind. Asking for uranium otherwise was more like a kneejerk response. This is the first time my request was taken seriously."