Unobtainium has a unique magnetic field and properties of superconductivity, causing it to levitate.
On Pandora, the magnetic effect causes huge outcroppings of Unobtainium to rip loose from the surface and float in the magnetic vortexes. These huge islands, named Hallelujah Mountains by Earth's explorers, are called Thundering Rocks by the Pandorans(Na'vi) , who hold them sacred. The unique magnetic properties of Unobtainium are used to contain and direct the energy of the matter-antimatter annihilation which propels ships like ISV Venture Star. Without Unobtanium, interstellar commerce on this scale would not be possible.
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