A rare element that has the power to change the days of the week around. It could also simply be a time-altering device. Zurg had it in his possession in the short comic Monday, Monday and turned Friday into Monday all across the galaxy, but it was snatched from his possession when XR and Buzz thwarted his scheme.
The main power source in Buzz Lightyear of Star Command, crystallic fusion is primarily mines from the underwater caverns of the planet Bathyos. The crystal itself is shown to be a light shade of green and faceted.
Only Bathyos and the unnamed mining planetoid in "Shiv Katall" were seen to produce crystallic fusion crystals.