sedimentary

Petoskey Stone

Hexagonaria percarinata

AI-generated identification · may be incorrect

Hardness: 3-3.5 (Mohs scale); Color: Gray to tan, white circles; Luster: Dull to vitreous when polished; Structure: Fossilized rugose coral hexagonal patterns; Specific Gravity: 2.7

Hardness: 3-3
Color: Gray to tan, white circles
Luster: Dull to vitreous when polished

Identified May 21, 2026More sedimentary →

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Physical properties

Hardness: 3-3.5 (Mohs scale); Color: Gray to tan, white circles; Luster: Dull to vitreous when polished; Structure: Fossilized rugose coral hexagonal patterns; Specific Gravity: 2.7

Formation & geological history

Formed from the fossilization of colonial rugose coral during the Devonian Period (approx. 350 million years ago) in warm, shallow tropical seas. Glacial activity later transported them.

Uses & applications

Highly popular for lapidary work, jewelry (pendants and beads), home decor, and as the official state stone of Michigan.

Geological facts

The name comes from Chief Pet-O-Sega of the Ottawa tribe. The distinctive pattern is most visible when the stone is wet or polished, revealing the radial structures of the individual coral polyps.

Field identification & locations

Identify by the unique hexagonal 'honeycomb' pattern. Commonly found along the shores of Lake Michigan and Lake Huron. Search for them on beaches after a rain or while wading in shallow water.