They can be obtained mainly by destroying Flux Tiles, which only spawn in Missions. You can also get them by trading, recycling a Handheld Pusher or other item made with flux, or by shooting it out of a critical Ship.
A usage example would be placing the Flux Crystals in a Machine Fabricator to craft
a Loader .
Used to craft
|All Resources / Fabricators|
|Metal • Explosives • Flux Crystals • Hyper Rubber • Silica Crystals|
|Starter Fabricator • Munitions Fabricator • Machine Fabricator • Engineering Fabricator • Equipment Fabricator • Legacy Fabricator|