fossil

Petoskey Stone

Hexagonaria percarinata

Hardness: 3-3.5 (Mohs), Color: gray to tan (turns distinctive hexagonal pattern when wet), Luster: dull to vitreous when polished, Structure: fossilized colonial coral rugosa.

Hardness: 3-3

Identified July 19, 2026More fossil →

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Physical properties

Hardness: 3-3.5 (Mohs), Color: gray to tan (turns distinctive hexagonal pattern when wet), Luster: dull to vitreous when polished, Structure: fossilized colonial coral rugosa.

Formation & geological history

Formed during the Devonian Period (approx. 350 million years ago) in shallow, warm tropical seas that once covered Michigan. Glaciation later distributed these fossilized coral fragments across the region.

Uses & applications

Used primarily in jewelry making, ornamental carvings, and as a popular collector's item and Michigan's official state stone.

Geological facts

The name 'Petoskey' comes from an Ottawa Chief, Pe-to-ga, meaning 'rising sun.' When the stone is dry, the pattern is often hidden, but it magically appears when the stone is wet or polished.

Field identification & locations

Identify by the unique 'six-sided' or hexagonal cells with radial lines. Most commonly found on the shores of Lake Michigan and Little Traverse Bay near Petoskey, Michigan.