Hi, @Angela-Baxter. Where in Michigan did you find this? We can use Macrostrat: https://macrostrat.org/map/#/z=1.5/x=16/y=23/bedrock/lines/ to figure out how old it is.

Hi @angela-baxter & @i-edwards – it’s certainly possible it’s banded chert! It’s hard to make a confident ID without more images. Chert would be pretty hard so if you tried to scratch it with the penny it shouldn’t make a mark. If it was calcite it may make a mark! Could be a next step test.

Hi @Angela-Baxter! I agree with everyone’s ID of horn coral. Would you be willing to update the taxonomy to reflect this ID? It would be Kingdom -> Animalia; Phylum -> Cnidaria; Class -> Anthozoa. We can also work together to figure out what age this is and what rock unit this came from.

Interesting specimen @angela-baxter. This certainly looks like a fossil. Are there any other features on the other side? And to confirm you found it in Michigan?

It’s possible it is a stromatoporoid, sort of a mat forming sponge that forms in interesting layers with bumps on the top. https://en.wikipedia.org/wiki/Stromatoporoidea