Possible Haxagonaria

[aps13034]

The rock on the right is a Petoskey stone but the rock on the left I am uncertain about. I found it in Alcona County, Michigan and it might be some sort of large celled Hexagonaria but I’m not sure. If anyone could help me identify it that would be great.

[Mark Kmiecik]

Most probably Hexagonaria alpenensis as it appears before tumbling in the surf on Great Lakes shores. Petoskey stone before being rounded into those "pretty" forms. You would have to count the septa. Not sure if you have enough detail for that. You could try grinding/sanding/polishing the backside to see more detail.

 

Species	Corallites (diameter)	Septa (count)
H. anna	12–16 mm	32-44
H. cristata	16–20 mm	36-44
H. fusiformis	6–10 mm	34-38
H. percarinata	~10 mm	38-40
H. alpenensis	2–6 mm	26-28
H. subcarinata	8–12 mm	30-34
H. attenuate	8–14 mm	30-38
H. potterensis	4–15 mm	36-38
H. profunda	13–15 mm	38-42

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