We need more than just one photo please. Some side views and views of both ends would really help. The outline says artifact but that doesn't mean it is one.
It looks like local stone. I found flint ballast in the same area and it's nothing like it. A scraper or similar tool was my first guess. It's almost too thin and oblong to be a gun flint. It could also just be a plain old broken stone but it stood out among the rubble on the beach and I thought it was interesting.