Found near Ouachita River in western Arkansas. What is it?

[penman77]

My buddy found this near the Ouachita River. It is very smooth, has a greenish tinge, and is egg-like in shape but is more slender.

Any ideas what this is?

 

[DetectingGodlikeOnOlympus]

It looks to me like a gastrolith, or "gizzard stone". https://en.wikipedia.org/wiki/Gastrolith