pic 3 looks like a softwood of some kind, im gonna guess pine. I could be wrong though. Sappy wood dont put it in your tank.
Does it smell like anything?
If it has that smell, it's probably not a good idea to use it. Too bad it is a cool looking piece.
If it smells like cedar, it probably contains oils that wouldn't be good for fish. Pines and cedars contain these oils.