Adamantine

Adamantine is born in the world's core and tougher than most metal. Most people regard it as unbreakable once it cools. The forges need to be as hot as the sun's surface (of which the metal gleams just as bright) and even then the metal is resistant to being hammered into shape. Warriors wearing rare adamantine armor can often stroll through battle without fear of danger, and adamantine weapons make quick work of any foe.