I don't like to take trees down; I normally buck the ones already laying on the ground. When doing this at a man's house one day, I encountered a tree with good, hard, heavy wood that seemed like oak. The man said the tree had been down a year or two. I cut it up, took it home, and named it Devilwood. Through a lot of sweating and swearing, I got all but one piece split (including tiny pieces that should not have caused any difficulty). That remaining piece is now my splitting stump.
I have since unmasked Devilwood as Sweetgum. As others have mentioned, the splitting issue is that the grains string apart rather than split. It takes extra hits and more energy to split Sweetgum.
Like any wood, there is an ideal time and an ideal way to split Sweetgum. I suspect that Sweetgum needs to be damp in order to split well. Both the trees I'm working on have some moisture in them.
I split solely by hand. At first, I tried setting wedges and hammering through the middle. Mistake. It turns into the jack-o-lantern shape that somebody else described. Work around from the outside, going parallel to the grain a couple inches inside the bark. You won't expect it, but the exterior pieces will pop off pretty easily. Once you split the outside off, you should have taken off enough weight to attack the middle.
The middle is just plain going to suck. Pick a good spot and get your axe to bite. Then, flip it over and hammer hard at high speed, thereby forcing the weight of the wood onto the axe. Repeat. Repeat. Repeat. Repeat. And, repeat. That's my best method of hand-splitting Sweetgum.
Is it a hardwood? Absolutely. Should it be sold as such? I haven't had the opportunity to burn it and compare it to oak, but I know that anything that requires that much effort will be sold by me as a hardwood. I suspect it will dry to be a god bit lighter than oak, but it still makes decent wood by appearance.
Seasoned and split, Sweetgum qualifies as hardwood firewood. It's really a waste of a resource not to use.
