Boronite

Boronite is a rare mineral ore, used in the synthesis of Omega molecules.

The Borg were able to synthesize a single Omega molecule using a quantity of boronite, but were unable to repeat the experiment as they never found another source of the ore.

In current knowledge, boronite is a copper-iron-sulfide ore, dark reddish-brown in color, with an iridescent surface film of tarnish.
Perhaps the rarer future boronite contains scientific properties we cannot distinguish of common modern boronite.
However, this seems unlikely; since boronite is quite a common substance on Earth, and since it is mentioned that boronite is rare, perhaps another substance is designated "boronite" in the future.