Ok, Thank you.
Could you please qualify your statement, as to why you're certain it's not an egg, or why it's just a rock?
Or what kind of rock or formation you think it might be.
It's very unusual. It's sort of a droopy sphere- and it seems to be made of concentric layers. You can see the outermost layer has cracked, and some pieces have fallen away. Just along the edges bordering the void, you can see a thin, lighter colored, shell-like second layer. Then, the third layer- and that's as far as I can see...
Does anyone have a little more insight as to what this might be?
This looks like a concretion and not a fossil. A concretion is where sediment is further hardened by the accumulation of minerals that have come out of soution in liquid and accumulated together. This often happens around a core which started off the mineralisation, forming spherical shapes with concentric layers like this one, which correspond to different phases of mineral accumulation or even different minerals being accumulated. The minerals further harden the sediment, so the concretion forms erodes out of the surrounding rock in tact.
The information sheet below explains about concretions. Where is the specimen from by the way? This is always important information.
Hope this helps!