Mandalorian Iron
this metal was first forged by the ancient Mandalorians, and the secrets for its creation were a closely guarded secret. It was made up from metal ores and certain minerals, and was virtually indestructible, even to a lightsaber blade. Jedi Master Arca hid Freedon Nadd's Sith artifacts in a storehouse built from Mandalorian Iron in an effort to seal it forever, but Exar Kun used the Dark Side of The Force to penetrate it.