I usually create my own fantasy metals in each setting. Sometimes the scales, bones, teeth, horns, and claws of powerful monsters can also be tougher than most metals, so they're used to create equipment too, and equipment is not always just metal mined from a mountain, but a combination of many things.
I usually never use Adamantium that much, but it is related with Adamas, which is Diamond, the toughest material known to man. Usually its a rare metal. Mithril is quite common, and I often make it different by being infused with different elemetnal properties, such as Red, Sunlight, Abyssal, and Spiritual variants.
Orichalcum tends to be a metal related with the gods, a Divine Metal that mortals simply cannot mine nor find naturally. it often times either gifted by the gods to someone, or its what composes ancient divine relics. In one of my settings, the Gods obtained Orichalcum from the blood of an alien race they enslaved, who were incredibly powerful metal-based lifeforms resembling giant golden sphynxes. Because of this it has unique properties unlike any other metal, and when heated enough it can even move on its own as if it were alive. But when hardened at lower temperatures, it can become so tough that nothing can break it, its magic conductivity is null too, cancelling magic attacks with ease.
Same here. Something like this.
