General "Did you Know?"s

[gamemaster1991]

Any type of gem, crystal, material, ECT that is hard to find, obtain, or find that serves some sort of plot point in a piece of fiction or a thought experiment is dubbed unobtainium.

So no. James Cameron did not make up a stupid name for the hard to get rocks in Avatar. However, a good writer would know NOT to use the ad-lib word in the final script.