i do not believe that is black walnut. i have some good chunks of black that came with a load of mixed hardwood i got but set it aside for firewood. it is very dark, almost black and very dense. ill see if i can find a pic of it to show you but what you have there doesn't even remotely look my black walnut.
Meadow Creek TS250, Horizon 20" Classic Backyard Smoker, old style weber performer