Galvinium X was a very rare mineral which could be used to make powerful explosives. It was found in large quantities on the planet Vortis. The Menoptera were captured by the Skirkons and forced to mine for Galvinium X until they were saved by the First Doctor, John and Gillian. The Skirkons were killed when the Doctor blew up their base by firing at the Galvinium X they had stockpiled. (COMIC: On the Web Planet)