Marionium was a substance with a metallic structure that was considered the most unstable element ever discovered on the planet Sunspot. Along with petonium, marionium was mined in the mines of the settlement Ran Dan's Folly.
In 25,793 BBY, in one of these shafts, Stargazer Dalien Brock used a marionium cube to charge the Gree device with dark matter, which when activated, he planned to launch a Gree Hypergate with in the Old City of the planet Tython.