Rogerium

Rogerium was known to the Romulans as one of their most efficient efficient fusion fuels.

When Soran told the Romulans that his forcefields and trilithium priming process would consume their reactor's fuel much faster than they were accustomed to, they told him this and that a nearby planet, Galorndon Core I, contained mass quantities of rogerium. (Star Trek video game: Generations)