Maldanite

Overview

Maldanite is an ore that absorbs magical energy. In short the world and everything in it passively generates low amounts of magical energy. However in high concentration areas maldanite will grow rapidly and more abundantly there.
The ore starts out as a small white crystal, then a golden bronze colored substance grows around it and together they both grow in size over time.
It's the maldanite core or crystal that absorbs and stores the magical energy. While its thick shell encasing it grows as more of a byproduct.
At a certain point when maldanite grows within big enough and relatively close to each other they actually start to leak magical energy of their own. This causes them to start to float, bringing land and water with it. All of the floating islands throughout the world are floating because of an abundance of maldanite trapped within thier soil.