It appears that nobody has written about the names of fictional elements (or other such matters as particles, alloys, etc) on this blog before. I happened to be looking up impervium and unobtanium recently, and came across handwavium, balonium and wishalloy. These are excellent words, all new to me, and in a different category, I would have said, than fictional materials such as dilithium, mithril or ice-nine.
I had also not known that adamant (or adamantine) was essentially Classical impervium, being a fictional or theoretical substance that was named for embodying resistance to damage. Chaucer uses it—I’m sure Chaucer would have used some relative of balonium, too, which would probably then have entered Modern English as a classy, poetic and somewhat archaic form of bullshit.