While Hexagonaria percarinata fossils can be found in different bodies of rock throughout the world, Michigan’s Petoskey stone only originates from a band of limestone deposited in the middle-Devonian. As sea-floor silt buried the lower portions of a reef, the corals were preserved in the resultant limestone and buried beneath layer upon layer of later rocks, where they remained for millennia until the most recent glaciers revealed them.
Petoskey stone largely formed within a particular layer of sedimentary rocks called the Gravel Point Formation, itself a part of a larger group of rock layers known as the Traverse Group, all deposited as a result of settling ocean sediments during the Middle Devonian. The Traverse Group is composed largely of limestone, but also of layers of shale; fossils of many different kinds are prevalent within all of the group’s rocks.