Luthorite

A fabulous "new metal"—described as the "hardest and strongest [metal] of all"—that is created by Lex Luthor in November-December 1946. "Luthorite resists friction-heat!" explains Luthor. "[With it] I can build irresistible weapons and impenetrable space ships to dominate the universe!" Luthorite contains iridium and possibly osmium, but its chief ingredient is "the unknown Element X," available only from certain rare meteorites. Luthor uses it to cover his wormcar to get inside impenetrable vaults. Trying to get away from Superman, they go all the way through the center of the earth and out into China. The Man of Steel then destroys the wormcar, uses the Luthorite to make handcuffs and chains, and uses it also as prison bars to hold Luthor. (S No. 43/3, Dec 1946: "The Molten World!")