Hymetusite was a radioactive material found on Aneth. It looked like dark-grey rock and could be used for fuel (for both the Nimon black hole maker and the Skonnan ship). It was stored in clear globes, apparently to protect against radiation. (TV: The Horns of Nimon)
Hymetusite could also be used to form part of a cold fusion generator. (PROSE: Lucifer Rising)