I vaguely recall Geo-Force being resurrected by the Earth itself, in his first appearance, and thinking that was a neat concept (and could perhaps explain Terra's eventual return from death?).
I wonder if his family has some sort of mystical / ancestral connection to the land of Markovia itself, and have sort of taken it to extremes to manipulate earth and stone outside of their original territory, at the cost of some of their mental stability. Perhaps if they stick to Markovia's bounds, they can connect to the earth and stone without flipping out, but the more they exercise their abilities outside of their traditional Markovia lands, to which their family originally bonded, the more conflicting elemental signal they are fighting against, and the more unstable they become...