Ceruleum is an energy source in Final Fantasy XIV. Ceruleum is a refined form of Aether, obtained by draining elemental Crystals of their energy, usually in processing factories. It is a powerful yet highly unstable source of energy, mainly used by Garlean Empire to power Magitek engines.
The Garlean Empire consumes vast amounts of Ceruleum to fuel their Magitek engines, powering anything from airships to armored tanks. In Eorzea, Ceruleum is only found in a small swath of mountainous land located in northern Thanalan. This Ceruleum deposit is monitored and controlled by the leaders of Ul'dah, as it falls within their land. Eorzean citizens use Ceruleum to power their airships.