Fossilized eggs?

[Highranger]

In some sandstone caves on my property there are layers of conglomerate stones laid into otherwise fine Hawkesbury sandstone. In amongst these there are hollow egg shape structures, some broken off but one in particular in intact but with a hole in it showing that it is hollow. They are all embedded in the ceiling of the cave.

the one featured is about 4 inches long.

Can some one tell me what they are likely to be?

 

[Rockwood]

Sorry. This looks like iron rich concretion to me.

[Pterygotus]

 Agreed, not eggs .

[Ludwigia]

Like Rockwood said.

[Highranger]

Thanks, I thought it would be too much to hope for. I really appreciate the quick response from all of you too.