Cortheum was the rocky form of the gas Corthel. A valuable mineral, Cortheum was used in the manufacture of droid photoreceptors. Veins of Cortheum were discovered on the planet Nurstin in the Bissillirus system. Settlers on the planet Draenell's Point in the same star system sent expeditions to investigate strange flashes of light emanating from Nurstin's surface. Upon investigation, they discovered the light flashes were the result of high concentrations of Corthel in the atmosphere, and large amounts of Cortheum were buried meters below the surface. Miners began to excavate the mineral, until Messert Mines Corporation received an Imperial charter and exclusive mineral rights to Nurstin.