They are definitely Hickory nuts. Hard to crack but delicious. The taste is similar to hazel nuts. Not many people collect these in these modern days but years ago they were a delight for home bakers. Use the same as walnuts. If you can get these before the squirrels do you're in for a treat.
I wish the picture were a little better. I vote for the hickory nut because they are too small for an English walnut. This looks like hickory nuts that have been hulled. We had several hickory trees in our yard when I was a child, and the nuts made a good snack for us kids.