Exactly! At home, it could draw power from a network of other runestones. Or from the planet itself! That's why I think it should be able to draw power from the Core.

[She coils her hair around herself to create a sort of chair she can lean back in.]

But I know there's a way to draw power out of it, too. There was someone at home who could do it and use it to attack people. I'm not totally sure if that power comes from the garnet itself, though, or if that's also being drawn from the network at large. If it's the latter, it's doing it in such small amounts that it makes no difference.