After 2.5 in-game years on our multiplayer server, we prospected the complete area around our current "village." We found multiple massive depots of Pentlandite. Actually, most ore in our area is Pentlandite.
However, at the moment, Pentlandite and Nickel are useless in the vanilla game. In the real life, nickel is used for stainless steel and alloy steel, which means in-game Nickel might be used to improve steel at some time.
Does a plan exist for Pentlandite or should we just leave it in the mountains?