Well, The Petoskey stones are composed of petrified skeletons of Hexagonaria percarinata. This is a type of coral from coral reefs that once well covered all of what is now the state of Michigan, the USA, during the ancient Devonian period, around 350 million years ago. The Petoskey stones were molded as a result of glaciation, in which sheets of ice scrapped the bedrock, gathering up fragments, and then grinding off their uneven edges and putting them in the northwestern portion of Michigan's Lower Peninsula. Ultimately, Petoskey stones are just chunks of coral reef, and when they dry the stone look like normal limestone but when wet or polished, the characteristic mottled pattern of the six-sided coral fossils emerges.
This primeval fossil is bringing into being across the state of Michigan along lakeshores and rivers in sediments usually called the Traverse group. Meanwhile in 1965, the Petoskey stone is called Michigan’s official state stone. Therefore, more than 350 million years ago during the Devonian period, Michigan was quite dissimilar. Geologically, the region was located near the equator and covered by a warm, shallow, saltwater sea, wherever the colonial coral hexagonaria percarinata flourished with other marine life in tropical reefs. Moreover, then the earth’s plates moved and pushed Michigan north and above sea level. When glaciers came about two million years ago, the land was scraped and the fossils spread across the northern Lower Peninsula. The stone was named Petoskey because they are bringing into being in great profusion in the Petoskey area.
Well, the name Petoskey derives from “Petosegay”, the son of an 18th century Ottawa chief, and it means “rays of dawn” or “sunbeams of promise.” The city of Petoskey was also named after the same person. However few say, the coral pattern in the stone resembles sun rays radiating from small suns.
Hexagonaria percarinata comprises of firmly packed, six-sided corallites, which are the skeletons of the once-living organism. So, at the center of apiece corallite was the mouth, enclosed by tentacles that were used for collecting food and drawing the food into the mouth. Though, this dark spot, or the eye of the corallite, has been filled with silt or mud that petrified after falling into the openings. Calcite, silica and other minerals have swapped the original soft tissues, called polyps, in each cell.
Petoskey stones can be originate from the shores of Traverse City, north to the Charlevoix and Petoskey area, and across the state to Alpena, but the most popular place to hunt for them is at Lake Michigan beach. Spring is a good time to look for the stone after the ice has melted and uncovered specimens that they’ve pushed against the shore.