It looks like an egg.

[WiredEFX]

Found this along the White River in Pike County, IN. I couldn’t find the other half. The closest I can find to this is called a Weaubleau egg. A product from several impact craters which is found between southern Illinois across Missouri and scattered around the Midwest.

 

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[DiggityDiggity]

sigourney weaver might be able to confirm. cool find!

 

[A2coins]

Thats a pretty cool find hope someone has more info on it , very interesting find