Introduction

The Petoskey stone is the single detail most associated with this town's name, and it holds up to scrutiny — this is a genuine geological identity, not just a tourist-shop marketing angle. We checked the actual science and the official state designation behind it.

What They Actually Are

Petoskey stones are fossilized colonial rugose coral, specifically the species Hexagonaria percarinata, dating to the Devonian period — commonly cited at roughly 350 million years old. The coral originally formed in what's now called the Alpena Limestone, part of the Traverse Group of rock formations.

How They Ended Up Scattered Across the Region

Pleistocene glaciers, roughly 2 million years ago, plucked and scattered the fossilized coral across northern Michigan within glacial till. Subsequent wave and stream action rounded the fragments into the smooth stones now found along local beaches and shorelines — the reason they're specifically associated with this stretch of Michigan rather than being a phenomenon found evenly across the state.

Michigan's Official State Stone Since 1965

The Petoskey stone became Michigan's official state stone through House Bill 2297, passed by the state legislature in May and June 1965 and signed by Governor George Romney on June 28,

1965. Chief Petosegay's own granddaughter, Ella Jane Petoskey, attended the signing — a genuine link back to the town's namesake.

Not the Same as Michigan's State Fossil

Worth getting right: the Petoskey stone is the state stone, not the state fossil. Michigan's separate state fossil is the American mastodon (Mammut americanum), designated by a different law entirely, Senate Bill 397, in March 2002 — nearly four decades after the Petoskey stone's own designation. The two get conflated online fairly often.

Practical Tips

• If Petoskey stone hunting is your goal, local beaches and shorelines around the bay are the general target — the stones show up scattered along the shore rather than concentrated in one single spot.

• Don't confuse the Petoskey Stone Festival with an event held in Petoskey itself — it's actually in Eastport, near Torch Lake, on the Saturday before Memorial weekend (see our Best Time to Visit guide).

• A polished, wet, or freshly rained-on stone shows the hexagonal coral pattern far more clearly than a dry one — worth wetting a candidate stone before deciding if it's the real thing.

Sources and Verification Notes

The coral species identification, geological age, and glacial-scattering explanation were checked against Michigan.gov's state symbols documentation and independent geology sources. The 1965 state stone designation and Governor Romney's signing were checked against contemporary reporting and the Mackinac Center's state-symbols history. The 2002 state fossil designation (American mastodon) was independently checked as a separate law, since the two designations are frequently and incorrectly conflated in casual sources.