Mirkanite
From Wookieepedia, the Star Wars wiki.
Mirkanite was a material found on the planet Mustafar.
It was a substance commonly used in the construction of superlasers, and indeed, the Galactic Empire tapped the planet for its resources during the construction of the first Death Star. Rianna Saren, a mercenary with the Alliance to Restore the Republic, destroyed the mine on Mustafar during her mission to gather information on the Death Star for the Rebellion.
