Orichalcum

The ancient Atlanteans invented a unique metal alloy called orichalcum, a hybrid creation of advanced metallurgy and alchemy. The secret of its creation was lost in the sinking of Atlantis, and likely would not be practical in an aquatic environment, but samples of the metal still exist, owing to its near-indestructible nature, and Atlantean “cold-forges” can reshape existing orichalcum to a degree.
Orichalcum is a tough golden metal with immunity to damage from temperature extremes. It also holds enchantments well, and many ancient Atlantean artifacts made of the metal have magical powers. Orichalcum weapons, armor, and tools are prized heirlooms among the Atlanteans and Utopians.