Dross

So. As it happens, there is a particular volcano in a particular place that is rather further north than you might expect. It's dormant, and since it's in kind of the wrong place, most people tend to miss it.
E/N: It's a shield volcano in Vielene/Valgrozna. You're not getting out of explaining the details so easily, Ruby.
This particular volcano has a very particular kind of lava, due to the type of stone that's been melted down. Essentially. And the exact mix is something I found quite useful, once I was able to properly store it.
E/N: It took her ages to figure out how to store it without ending up with burning lava on her hand or having to deal with its unique properties. The process was more luck than skill.
I call the material Dross, because when I write it down on any kind of document people think I'm referring to the waste products in other refinement procedures. This way I don't have to share. Even when people find out it's potentially quite interesting, the name gets them to underestimate what it's capable of.
It's really useful for lining one's lair so that it's better defended. Repels a lot of different kinds of energy attacks and such, and with the right application of electricity can even render it largely invisible.
E/N: And all that pales in comparison to the fact that she uses it to shift things through dimensions. This material does not exist exclusively on our plane of existence. But sure, she uses it for her lairs.
With how it reacts to different forms of energy, it can be quite difficult to gather, since you risk severe burns and also the complete destruction of your equipment under the wrong circumstances.