Air test=swipe rock over detector coil, check ID.
This really looks like a natural mineral formation. The green color just really has me scratching my head...looks alot native copper rocks from the UP...but it would be a long ways from home in this case. Though copper nuggets did get traded far and wide, could even be an indian artifact.
It also resembles something we find here...the coal clinker. Metals, either natural or introduced, get oxidized in a coal burning furnace, mixed with coal ashes to create a light weight, pourous rock that make detector go nuts. But I haven't seen any green ones...
It's not a space rock. If it's heavy and compact my vote is for native copper mineral formation...if it's light weight it's more likely a coal clinker. Native copper also known for containing silver...this might be a good one to slice open and polish. Looks like a pretty good keeper to me.