There's no argument here. Unobtainium is more widely accepted and has been around longer than unobtanium. It is the original spelling used since the 1950s. Search results on Google bring up 900,000+ for Unobtainium vs 400,000+ for Unobtanium. This is like comparing Lol and Lul to see which one is right. Some celebrity can use Lul as a spelling in a movie but that will not affect the original.
I mention James Cameron because he does extensive research for his films, and he even created a fully functioning language around the navi people which was rumored to take almost an entire year.
No James Cameron did not create that language. Paul Frommer did.
You will see it is actually 50/50 on the spelling.
32 unobtainiums vs 20 unobtaniums does not equal 50/50 of each.
Like I said though I'm fine with the spelling because it differentiates itself from the original usage of the word. Possibly James Cameron did the same so people will know his fictional ore as Unobtanium and not Unobtainium which has been separately used for decades.
