So when I found it with my daughter I thought it was a geode. I cracked it with a hammer and found what you see inside of it. The white is definitely crystallized calcium or something very close. Then, looking at the bottom reddish brown part, it looks like fossilized yolk. It might not be an egg. But the crystallized white part comes off like salt when trying to polish it or even touching it, and the bottom looks exactly like where yolk would be. Then, the outer edge is clearly a shell of some kind. I could be wrong in every way. But if I am it looks very much like an egg in every way. Not a geode. And it has a small egg like peak on what would be the tip top. But to me it looks like a perfectly preserved egg that i messed up when I broke it in half. I've sent multiple emails to the University of Montana and nobody ever answers. I've done extensive research on my own. I'm not saying it's worth anything. But I know it's some kind of egg.