Yeah, there's tricks to splitting it. Start around the outside and work your way in. That's what the old timer was gonna show me, but this particular tree was like trying to split an anvil.
I don't have any trouble with elm, now that I'm "wealthy" enough to own a splitter, ha. Some of it will make the splitter cry the blues though.
Sycamore is what I hate to mess with. It's stringy, and won't separate until the last inch. It's undesirable as firewood, but I have a creek bottom that grows it too well, and if I cut it, I'm gonna burn it. It's spring and fall firewood - it just doesn't have the heat in it that hickory and oak have.