What is a Petoskey Stone?

Polished Petoskey Stone Coral Fossil (Hexagonaria, percarinata)

Simply put, a Petoskey Stone is fossilized coral. Why is it called, a Petoskey Stone? Because so many of its kind are found abundantly in and around Lake Michigan shores, especially near the Northern Michigan city of Petoskey (USA)!

They are also called “lucky stones” so it’s really great to find one!

How could the remains of a coral, which thrived in tropical warm waters, possibly find its way to Michigan?

Because during the era they lived, around 416 to 369 million years ago (Devonian Time Period), much of North America was more tropical and was covered under warm shallow seas. Later, the corals were buried under deep layers of sediment. Many millions of years after that, when the great glaciers retreated, they scraped and dug into those forgotten layers of earth. The glaciers deposited them where we can now enjoy the good fortune of discovering their mysteries.

Rough unpolished Petoskey Stone Coral Fossil (Hexagonaria, percarinata) found on Lake Michigan beaches.

Petoskey Stone fossils originate from mass coral colonies of Hexagonaria, percarinata. Each hexagonal corallite (visible in the stone) held a single animal which opened a mouth exposing tentacles that siphoned food particles floating by in ocean currents. The tentacles were also used to sting any organism or other corallites that came too close. Calcite, silica and other minerals replaced the original exoskeleton over many millions of years.

Corallites Detail of Petoskey Stone Coral Fossil (Hexagonaria, percarinata) found on Lake Michigan Beach


Common Name: Petoskey Stone or Lucky Stone

Scientific Name: Hexagonaria, percarinata

Kingdom: Animalia

Phylum: Cnidardia (means to sting)

Class: Anthozoa (ie coral, sea pens, sea anemones)

Subclass: Zoantharia (true corals)

Order: Rugosa (means wrinkled wall)

Family: Hexagonaria (means six sides)

Species: percarinata

Petoskey Stone Coral (Hexagonaria, percarinata) Rendering Drawing

All rights reserved © Fossillady 2022