Nebulite

Nebulite is a very durable metal, presumably exclusive to the planet Nebulos.

Fiction

Ladybird Books continuity

As Scoop finished burying the Decepticons under layers of rocks, Quickmix decided the barrier wasn't sturdy enough yet and could use a little extra. He ordered Scoop to collect a heap of fine sand and as much of the metallic gravel nebulite as he could find. Mixing the two components with water and cement from his own storage tanks, Quickmix created a nebulite-concrete he assured the others would take the Decepticons quite some time to break through. Decepticons Underground

Ask Vector Prime

In a minor Tyran universe, Vector Prime once had quarters with a vent connected to the engine room of the Steelhaven. He grew to find the smell of nebulite quite unpleasant over time. Ask Vector Prime, 2015/06/14