Illerium was a valuable chemical that was often smuggled to needed worlds.
Illerium was highly volatile, especially when exposed to air. This property made it a necessary part of the manufacturing of starship ejection seats and escape pods, as it supplied the necessary force to propel the vehicle away from its ship. It could also be used in much the same way as detonite, but with much smaller results.
During the Galactic War, a radioactive variant called isotope-5 was found on Makeb.
- The Complete Star Wars Encyclopedia