After examining the split piece more carefully, I lean away from burr oak because the bark is too thin. Burr oak bark is thick and coarse. I cut and burned two cords of it last year from trees that had been dead off the ground for several years.
And, as I said before, I have never seen oak heartwood have that much contrast between the sapwood and the heartwood so well defined. The rather curly grain also tempts me to day that this sample is in the applewood family, which when dried thoroughly, is also an absolute bear to split.
Another dandy that when dry is very tough to split is pearwood. Dry wood from the Bradford and Cleveland pear trees will sound like a cherry bomb when split using a 20-ton powered log splitter because it gives up so suddenly. However, ornamental pearwood is orange in color and more uniform throughout the log.
So, I think TreeCo needs to chime in here and help us out with this identification. Where is he, anyway?