sedimentary
Petoskey Stone
Hexagonaria percarinata
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
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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.
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