Should I be concerned?

[Djgm]

1/2 the flock is starting to end their molt…and today I found this egg in the nesting box. Everyone seems to be acting fine, eating fine ect….and of course everyone lays brown eggs so I don’t know who laid it. The entire shell is hard, including the tubeish part on top and it's also very tiny. I’m in North Jersey and we just got 7+ inches of snow and it’s been low teens. Girls don’t free range (not allowed in my town) so they couldn’t have gotten into anything. Have heaters for the water, they’ve got grit oyster shell ect…do I need to be concerned?

 

[Wyorp Rock]

Can you crack it open?
Likely a fairy egg that stayed in the shell gland for a while.
Whoever laid it probably is working on another egg by now. I would just observe the hens and take note if anyone looks off. If so, then see that she's drinking and give her calcium if you have it (Caltrate with D3 is best).