fossil

Petoskey Stone

Hexagonaria percarinata

Hardness of 3 to 4 on the Mohs scale, colors range from grey to brown, dull to waxy luster when polished, hexagonal coral corallites structure, specific gravity around 2.6 to 2.7.

Identified August 3, 2026More fossil →

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Physical properties

Hardness of 3 to 4 on the Mohs scale, colors range from grey to brown, dull to waxy luster when polished, hexagonal coral corallites structure, specific gravity around 2.6 to 2.7.

Formation & geological history

Formed from the fossilization of colonial rugose corals during the Devonian period, approximately 350 million years ago, in shallow warm seas that once covered Michigan.

Uses & applications

Popular in lapidary arts, jewelry making, ornamental carvings, and as a collector's item or souvenir.

Geological facts

The Petoskey stone is the state stone of Michigan. The name comes from an Ottawa tribal chief named Pet-O-Sega, which means 'rays of dawn'.

Field identification & locations

Easily identified by the distinct mottled, hexagonal pattern of fossilized coral eyes which become much more prominent when the stone is wet or polished. Commonly found along the shores of Lake Michigan and Lake Huron.