It's not just a rock, it's a piece of worked lower quality Hixton. The little notch may or may not be intentional. Little notches like that are often referred to as "shaft scrapers" but the truth is that the many are just accidental from human hands or the plow. Notched tools like that could have also served as tools for a number of other things like cutting/stripping pieces of basswood for making string and baskets, without doing a use wear analysis with ultra high magnification it's almost impossible to say for sure. Keep hitting that area, I'm sure there's more Hixton there and that was mined and used throughout all of pre history.