Yes sweet gum is tough to split, near impossible by hand. I have had elm and sycamore that is worse to split. A lot depends on the tree. It is probably not the greatest firewood for heating, but sufficient for an open fireplace IMO. Most of my firewood customers just burn firewood in an open fireplace. I separate the hardwoods for my customers that actually heat with wood. Currently, my mixed stacks have elm (red and white), hackberry, silver maple, ash, yellow pine, sweet gum, and birch. I have had sycamore and soapberry in the past also. Can't think of anymore at the moment. The only wood I have turned down is willow and catalpa. I personally have a fireplace only and burn anything. I now save all the good stuff for the customers.