Stardust is pure nebulae that's been condensed into a solid. It's a valuable substance--even more so than gold. Most mining towns are in areas where stardust has been found.
Stardust can be used to increase the effect of spells. It's also a necessity for alchemists--their potions wouldn't work without stardust to power them. More advanced technology also needs stardust to run.
Quasars are the heart of any machine that uses nebulae for their functions. They're made using stardust and special blacksmith techniques. The circular core holds the important information, while the outer rim is used to control it. All buttons on the rim are embeded into it, and a full keyboard can be displayed from most quasars.