Rubindum ore was a type of mineral integral to the construction of hyperdrive engines.
History
While serving aboard the Rand Ecliptic, Biggs Darklighter and Derek Klivian were assigned to deliver a shipment of rubindum ore to the Imperial Naval shipyard in the Bestine system. Instead of locating the shipyard personnel, Darklighter and Klivian sought out Klivian's friend Lindy, who put them in touch with the Alliance to Restore the Republic, to whom they hoped to defect.
While attempting to escape Bestine IV in the stolen Ecliptic, Darklighter dumped half of the shipment of rubindum into the path of pursuing TIE/LN starfighters. The rubindum created a small-scale asteroid field. Few of the fighters were able to evade the lethal ore, allowing the Ecliptic, its fugitive crew, and the remainder of the valuable ore to escape into hyperspace en route to a new life with the Rebellion.
Behind the scenes
The Essential Guide to Characters refers to the mineral as rubindun.