Found this here in Kentucky while looking for arrowheads. Really heavy and very smooth. Found just like this just cleaned it up. Any ideas? Thanks for the help!
It's a neat-looking concretion that has broken open to expose the interior and then been very heavily water-eroded. They usually have a shell and an interior with different compositions of iron-rich material (lithified clays, carbonates or whatever) including limonite or siderite and other iron minerals in varying combinations.