Boridium

Boridium (symbol Bo) is a chemical element, atomic number 121 on the periodic table.

Characteristics and history
Boridium, in its most stable form, has an atomic mass of 317, and was discovered by the Federation for the first time through contact with the civilization on Rigel IV. This metal is part of the trans-uranic series of heavy elements. 

Background
In real-life science, element 121 has yet to be discovered. A placeholder name based on its number, "unbiunium", has been suggested to document the possible existence of this substance. Some models of theoretical science have stated that heavy elements on this scale may be impossible to synthesize or reproduce, and cannot exist in nature. Subspace science mentioned in Star Trek may account for the contradiction of this being a natural resource on other worlds.