Adamantine

Adamantine is a black metal with a slight purple sheen, mined deep within the earth, that is harder, stronger and heavier than steel. The dwarves monopolise the supply of adamantine, as only they have the expertise to dig deep enough to extract it. Thus, wares of adamantine are highly prized and sell for a massive mark-up on the surface. The dark elves mine and work it too, though trade so rarely with the surface that this is not common knowledge.