What is this?

[aps13034]

I found this fossil in the Black River, Alcona County, MI. I have no idea what it is. The zigzag parts seem to go all the way through. It’s probably Devonian because most rocks in the area are.

 

[Fossildude19]

Looks like maybe a Halysites sp chain coral, embedded in matrix. 

[DPS Ammonite]

@Fossildude19  I do not think that it is Halysites  coral because the the branching and meandering light structure in the OP’s rock is a boundary between adjacent holes/ corallites. The whole rocks shows holes and it probably another type of coral or a bryozoan. A better close up photo would be helpful.

 

In Halysites the chain consists of the corallites themselves with lots of space between the corallites. See photo of Halysites from Louisville-fossils: 

 

 

and detail of OP’s fossil.

 

[Herb]

looks like a bryozoa to me also

[Shamalama]

Can you get a closer view of the zigzags? Maybe some more detail will give a clue.

[supertramp]

tiny Archimedes sp.?

[Mark Kmiecik]

I'm leaning towards Graptolites .

[Micah]

No idea, but I’m curious what we’ll conclude. I’ve not seen anything quite like that before.

[Kentuckiana Mike]

I think what you have is a crushed Favosites coral. See the Friends of the UMMP Michigan Basin Specimen Database web site and look at those types of corals. 

 

The living chamber walls broke apart where one cannot make out the hexagon and pentagon shapes. Below is a link to a Favosites hispidus found in Chippewa, Michigan, note the zig-zag like patterns on cell walls.

 

 

[Pippa]

Like Mark, I thought of graptolites right away, but I think the zigzag pattern on those is seen only on one side of the fossil unlike your fossils.

 

Mike's zigzag favosite above makes a lot of sense to me. It would also explain how the zigzags are distributed on the rock forming such a regular pattern and that they continue all the way through the rock.

 

One sided zigzag edge of graptolites:

[Packy]

Could you take closer photo maybe with a microscope ?

[aps13034]

Here’s some pictures of it polished.

[Mark Kmiecik]

It polished well. Hard to see any detail. The photos are a bit blurry. Probably 1000% better viewed in person.