Newbie in need of identification

[bamontgomery]

Hi, all. I was a rockhound as a kid, but sort of let it go for the last thirty years. Last month my family and I were on a Lake Michigan beach in the SW corner of Michigan, and my wife, our son, and I began to pick up anything that looked interesting. None of us really knew what we were doing, but we came across some small fossils and a few other things. I found this stone which appears to have something inside. Can anyone tell what it is from the picture?