Honeycomb?

[Caroline Grace]

This fossil looks like a honeycomb. I doubt its coral, if you look closely the holes are almost all perfect hexagons. 

It was found in northern Michigan (lower peninsula) 

What could this be?

[ynot]

That is coral, just really worn down.

[Doctor Mud]

Was this near Petoskey MI?

 

Fossil coral is very common there, there are large fossilized reefs that erode onto local beaches.

 

Petoskey stones

 

https://en.m.wikipedia.org/wiki/Petoskey_stone

 

 

[izak_]

Yep, thats coral. They commonly have perfect hexagons.

[Doctor Mud]

Hence the name of the genus of coral:

 

Hexagonaria