Hexagonaria
percarinata
The “official “state stone” of
Michigan is the Petoskey Stone, the local name for rounded pebbles or
cobbles of the fossil coral Hexagonaria percarinata Stumm, 1969.
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 consists of many
lithologies, including fossiliferous limestone clasts and worn fossil corals
(favositids & colonial rugosans). Hexagonaria is a colonial
rugose coral (Animalia, Cnidaria, Anthozoa, Rugosa, Phillipsastraeidae).
Hexagonaria percarinata (field of view 3.2 cm across) - “Petoskey
Stone”.
Hexagonaria percarinata (field of view 2.6 cm across) - “Petoskey
Stone”.
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.