Mithril

Mithril, also sometimes called true-silver, true-steel, or elf-steel, is a rare and precious metal with nearly miraculous properties. It is as strong as the best steel (or even stronger), but much lighter, with a silver-white luster that never tarnishes, and it takes to enchantment exceptionally well. It is mined exclusively by the dwarves, who consider it one of Urugan's sacred gifts and who alone know how to find hidden veins of its ore deep in the roots of the mountains. Dwarven smiths preserve many secret techniques for the working of mithril and the making of various alloys from it, and use it to forge arms and armor of wondrous quality. 
However, it is also loved by the elves, who buy it at great price from the dwarves and have their own methods for its use. The best elven artificers can create mithril objects of no less workmanship, and arguably even greater beauty, than those of the dwarves. It is because of the elves' love for mithril that some call it elf-steel, despite the fact that they do not produce it themselves.