My Top Ten Unobtainiums

Tonight I watched the latest Star Wars film Rogue One and once again had the topic of Kyber Crystals tossed onto my intellectual plate. This got me thinking about other such examples of Unobtainium on the small and big screen over the years.  This is my list of favorite mineral/metal substances that exist only in science fiction/fantasy.

1. Mithril ( Lord of the Rings universe)
2. Dilithium (Star Trek universe) 
3. Kryptonite (DC Comics universe)
4. Infinity Gems (Marvel Comics universe)
5. Adamantium (Marvel Comics universe)
6. Kyber Crystal (Star Wars universe)
7. Naquadah (Stargate universe)
8. Tylium (Battlestar Galactica universe)
9. Eludium (Looney Toons universe)
10. Mimetic Polyalloy (Terminator universe)

*Postscriptum: CrazyDave65 reminded me of Isaac Asimov's Thiotimoline.
**Post-Postscriptum: Linsis reminded me of Star Trek universe's Tritanium which was also appropriated by the Transformers' universe.
(Updated 1/05/17)