4.5" Polished Slab Petoskey Stone Hexagonaria Coral Fossil Devonian Age Michigan

Location: Michigan, United States

Weight: 2.9 Ounces   

Dimensions: 4.5 Inches Long, 1.9 Inches Wide, 0.3 Inches Thick 

The item pictured is the one you will receive.

Devonian Age, 350 million years old

Petoskey Stones are unique rocks that are also fossils, specifically the fossilized rugose coral Hexagonaria percarinata. Typically pebble-shaped, these stones are found mainly in the northwestern and northeastern regions of Michigan's Lower Peninsula. They are fragments of an ancient coral reef that flourished during the Devonian period, approximately 350 million years ago, preserving the intricate skeletal structures of these long-extinct corals.

Petoskey stones were formed through glaciation, where ice sheets plucked stones from the bedrock, grinding off their rough edges and depositing them in specific areas.  When dry, they resemble ordinary limestone, but when wet or polished, they reveal a distinctive mottled pattern of six-sided coral fossils. The Hexagonaria percarinata consists of tightly packed, six-sided corallites, which are the skeletons of the once-living coral polyps. The center of each polyp was the mouth and contained tentacles that reached out for food. The hexagon shape of each cell and thin lines radiating out from the dark “eye” in the center are distinguishing features unique to this fossil.

These ancient coral fossils await discovery across Michigan's most compelling geological sites. From the Lake Michigan shoreline stretching between Traverse City and Petoskey to remote inland locations, Petoskey stones reward patient seekers year-round. Winter's relentless ice movement naturally exposes fresh specimens, making spring the prime collecting season when the shoreline transforms. Visit celebrated hotspots like Petoskey State Park, Magnus City Park Beach, and Solanus Mission Beach, or venture beyond the beaten path into gravel operations and agricultural areas where exceptional finds still emerge. Each stone tells a 375-million-year story—start your collection when conditions are ideal.