Looks like just a non-descript rock. Here in the west, rocks that look like that are everywhere. Perhaps where you are in MI there aren't rocks that look like that ?
Theres just not enough in the pics for me to be of any help. If you are so motivated, you can always take any specimen to your local college geology department and ask there. A lot of rock/mineral shows will have a desk for id's too tho those shows are becoming gem/jewelry shows anymore.
It looks like limestone that has been out in the elements for a while to me. We have lots of it in Missouri and I use it to make stone fitted walls as it has a natural tendency to fracture in straight lines. I don't need to do much to make the fit together without using mortar (dry masonry).