Hexagonaria percarinata Stumm, 1969 - fossil rugose coral from the Devonian of Michigan, USA. (public display, National Rockhound Hall of Fame, Murdo, South Dakota, USA)
The “official state stone” of Michigan is the Petoskey Stone, the local name for rounded pebbles or cobbles of the fossil colonial rugose coral Hexagonaria percarinata. Petoskey Stones have been weathered & eroded from fossiliferous limestones of the Traverse Group (Middle Devonian). They are particularly common in the vicinity of Little Traverse Bay & the town of Petoskey (northwestern Lower Peninsula of Michigan). Beach & lake gravel in this area consist of many lithologies, including fossiliferous limestone clasts and worn fossil corals (favositids & colonial rugosans).
The city of Petoskey, Michigan gets its name from an old Ottawa Indian Chief, Ignatius Petosega. “Pet-o-sega” means “rays of the rising sun”. Petoskey Stones are so-named in reference to the dark-colored “eye” & radiating lines of individual Hexagonaria corallites.
The specimen shown here is mostly in its natural, rough state, which is unusual - most Petoskey Stones have been polished. The black colored area at the left has been polished to show the interlocking, irregularly hexagonal shape of the corallites.
Classification: Animalia, Cnidaria, Anthozoa, Rugosa, Phillipsastraeidae
Stratigraphy: Traverse Group, Middle Devonian
Locality: unrecorded/undisclosed site in Michigan, USA
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See info. at:
en.wikipedia.org/wiki/Rugosa
