Skystone

While attempting to save the world during the Sundering, Allanna created the Isles. As part of this process, she transformed great sections of quartz into a blue-white stone called Skystone. It is Skystone that causes the Isles to float.
Skystone requires an Alchemical Activator to work once it has been hewn from the Isle that birthed it.
Skystone is used extensively in the construction of Sky Galleons.