Floating Islands Kingdom CONCEPT

some time ago I made an illustration for a story I'm making. The illustration is about bird people living on a mountanious region surrounded by giant floating islands where their big buildings are held, while residential zones are on the top of the mountains. I find pretty cool making their houses out of "bird houses" (they being bird people...). Also I wanted to put some kind of reason for why the islands float, and there is where those crystals come. I imagine them as giant magnets, minerals hidden in the whole region. These islands are big chunks of land that separet from the rest of the mountains, being these magnets responsable of causing the detachment of the land.