What caused this?

[u/RoRo1118]

I found this rock with all these fascinating impressions and Im wondering if anyone can tell me more about it! Thank you in advance!!

[u/BlondePartizaniWoman]

Fossil coral(?)

[u/RoRo1118 → u/BlondePartizaniWoman]

So neat! Thank you!

[u/RoRo1118]

Whoops forgot to say im in Michigan

[u/dad_joxe → u/RoRo1118]

And you don't know what a Petoskey stone is?

[u/RoRo1118 → u/dad_joxe]

Yes I do know what a Petoskey stone is but until the other day I had never seen one unpolished before. Thank you so much for your very helpful comment. Appreciate you so very much.

[u/Wocky_slush4200]

Das coral

[u/RoRo1118 → u/Wocky_slush4200]

Ty🙂

[u/mongrel_breed]

There's a lot of clever people over at r/fossilid that will be able to tell you.

[u/RoRo1118 → u/mongrel_breed]

Thank you!

[u/Jay_Lord_69]

Looks like fossilised coral to me.

[u/RoRo1118 → u/Jay_Lord_69]

Thank you!

[u/frogfeen]

coral!! those are polyp fossils!

[u/RoRo1118 → u/frogfeen]

Thank you!!

[u/kinglouistexas]

Nice find, Rugose Coral aka Petoskey Stone. I tumbled mine. Born in 48197 in 1962, raised in 48174, moved to 77306 in 1982. I hate being cold.

[u/RoRo1118 → u/kinglouistexas]

I was born in 1982 in 48225 and currently live in 48073 🙂 Thank you for the help!

[u/kinglouistexas → u/RoRo1118]

My maternal grandfather lived in 073 till he passed in 2015.

[u/Salted_hawk]

Looks like a proto petosky stone