The Petoskey Stone, Michigan’s official state stone, is a coral that was picked up by glaciers and deposited in the northwestern portions of Michigan’s lower peninsula. These fragments from the coral reef were originally deposited in the Devonian Period about 350 million years ago! Petoskey stones are found only in Michigan, on many beaches of Lake Michigan and Lake Huron as well as in rock quarries from Traverse City to Alpena. Petoskey (Hexagonaria percarinata) is a roughly hexagon shaped coral with lines radiating from the “eye” of each hexagon. The polished coral fossil makes stunning jewelry and collectable art pieces.