Adamantine

This metal looks silvery but with a very distinct green sheen to it. It is also extremely dense and incredibly hard. While the metal is heavy, even a thin and light sheet of it can provide as much stability as a much more massive slab of steel. As such, adamantie items are usually much lighter than alternatives. Its durability means swords made from the material will never get dull and can cut through much more than their steel counterparts. Armour made from it won't dent from impact that would easily pierce other materials.

Of course, not all applications of adamantine are for combat. It is highly sought after for construction and architecture due to its durability and strength. And anything as expensive as this metal will lead to the wealthy using it to show how rich they are.