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[JunseiKei]

Where are you getting that information from?

The lorebook (in the page on Garlean history) describes ceruleum as a "natural resource", a deep-blue liquid that burns like oil, and I don't think it's been elaborated on beyond that. (We also see natural vents of it in the lowest levels of Cutter's Cry.) It seems intended to be fantasy-petroleum. Admittedly that doesn't disprove it being aetherially charged petroleum or something, but generally when crystals are used as 'aether batteries' they seem to dissolve entirely upon use.

Tidbits from 1.0 lore, sightseeing logs and wikis citing lore Q&As from the staff here on the forums. Supposedly, the blue fog from ceruleum is it being burned away. I'd imagine using a crystal as a battery is different than draining its contents for fuel and why one leaves an empty shell while the other removes crystal and aether entirely. That's not to say there isn't an oil form of ceruleum - but that doesn't mean it can't crystallize (given the little bits of information we've been presented - Mor Dhona is polluted with ceruleum both in water, air and land). Especially since aether is the power source in Hydaelyn.