Unobtainium

Unobtainium is an ore found in the Unobtainium Mines expansion, added in Alpha 8. It is currently the rarest ore in the game, not including Chronium.

Trivia

 * Unobtainium is not a new idea. Both Azure Mines and Avatar have their own versions of it.
 * However, Bismuth Mines' Unobtainium is much rarer, as it is not only exclusive to it's expansion, but it also has about a 0.004% chance of spawning.
 * Unobtainium was originally named Unobtanium, but it was changed due to it being a misspelling
 * The creator of the game, PloxGD, has only seen Unobtainium spawn naturally twice. Both times were during game testing.