You could post in the rock forum a little lower down the page and they can probably give better ideas of what it is.To me it looks like the glass you used to be able to blow that was a toy that was banned.In the 60's or 70's.
I am not downgrading your find I am just giving an idea this is a Mohs scale to test the hardness of the stone to eliminate some guessing.You could take to a gemologist but don't let out of your sight. https://www.nps.gov/articles/mohs-hardness-scale.htm
When I was a kid we use to find what looks extremely similar along the Mississippi River. I can still remember it because these were smooth and had similar angle to it which did not seem normal, but ours was a small rock for sure, at least up until we smashed it. We "theorized" it was so smooth due to being along the river for a long time.