Corpira

A corpira was a unit of extra-terrestrial currency. Although it was unclear where it was legal tender, Turlough had somehow come by a two-corpira piece, which he used as a way to determine his fate. On Frontios, he secreted it in a hand, and then had Norna choose which hand it was in. When she guessed correctly, he gave her the piece and then, somewhat reluctantly, set off to find the Fifth Doctor in the dangerous, Tractator-made cave system underneath the colony buildings.

He claimed that the two-corpira piece could be used to summon good luck, if the bearer blew through its hollow centre. (TV: Frontios)