Quote Originally Posted by Anonymoose View Post
I can't recall seeing ceruleum / crystal linked officially (just ceruleum and aether-based), but I'm going to keep an eye out again just to be safe.
Either way, the only information I can find on ceruleum in-game comes from the Immortal Flames commanders stationed at Camp Bluefog and the Ceruleum Processing Plant.

Edelstein (Ceruleum Processing Plant): "This facility was built to extract and refine the vast deposits of ceruleum that lie beneath the earth. ...The Garleans are heavily dependent upon ceruleum for their machina."
Cracked Fist (Camp Bluefog): "Lest you wonder, the name Bluefog is taken from the bluish haze that accompanies the extraction of that selfsame ceruleum."

Implicitly, ceruleum is to crystals as gasoline is to coal. We know it's deep underground, has to be extracted and refined, can be used to power machines, and is highly volatile. Like gasoline, it has to be refined from a liquid extracted from the earth, and doing so emits pollution. It's used for magitek - no airship could work without magic, and all Garlean tech is magitek - so it also has some aetheric properties to it. Dumping impure ceruleum into the shields surrounding the Praetorium in Castrum Meridianum was also key to Operation Archon, suggesting impure ceruleum is the aetheric equivalent to crude oil.

Might be more info in the Operation Archon battle plans, but I don't feel like combing through the cutscenes to find a line or two of dialogue in there right now.

Whether or not it can be extracted directly from crystals, well... who knows. I'd say it's possible (what with deaspected crystals). Most in-game crystals are a light blue, while corrupted crystals are yellowish... it might be that the impure ceruleum that can be extracted from corrupted crystals isn't suitable for refinement, or whatever the end product of "corrupted impure ceruleum" refinement is isn't energy or cost efficient.

Too many unknowns. Oh, if only I could tinker with such things in real life...