Pergium

Pergium is a radioactive element that has been found on various worlds, such as Argus X. It has an atomic number of 111 (Star Fleet Medical Reference Manual).

A survey of Wolf-catalogue stars within a 5-parsec sphere from Sol in the early 22nd century discovered that the fifth planet of Wolf 359 had reserves of both pergium and topaline (Star Trek: Shadowstar Station), which led to the establishment of the Yogyakarta Baru colony.