This strange thing was living with some corals, agate, concretions in red mud/clay.
From a road cut near the Ohio River, I cleaned it up and put it in water to soak hoping to soften the mud packed into the small hole, and it floats! It looks and sounds, and feels like rock/mineral and has tiny crystals on the surface. I cleaned it with soap and a nylon brush and the hole did open up. It is 7/8" long and 5/8" wide. It's max diameter is slightly less than a dime.