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 items made with flux, and sometimes by shooting it out of a critical Ship.
A usage example would be placing the Flux Crystals in a Machine Fabricator to craft
a Pusher .
|All Resources / Fabricators|
|Metal • Explosives • Flux Crystals • Hyper Rubber • Silica Crystals|
|Starter Fabricator • Munitions Fabricator • Machine Fabricator • Engineering Fabricator • Equipment Fabricator • Legacy Fabricator|