sedimentary
Petoskey Stone
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-3.5 (Mohs scale), Color: Gray to tan when dry, distinctive hexagonal patterns when wet. Luster: Dull to earthy. Composition: Calcite replacing original coral structure.
- Hardness
- 3-3
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-3.5 (Mohs scale), Color: Gray to tan when dry, distinctive hexagonal patterns when wet. Luster: Dull to earthy. Composition: Calcite replacing original coral structure.
Formation & geological history
Formed during the Devonian period (approx. 350 million years ago) from ancient rugose coral reefs in a shallow saltwater sea that once covered Michigan.
Uses & applications
Predominantly used for jewelry, lapidary art, and souvenirs. It is the official state stone of Michigan.
Geological facts
The hexagonal shapes are individual coral polyps. The name 'Petoskey' comes from Ottawa Chief Pet-O-Sega, meaning 'rising sun' or 'rays of hope'.
Field identification & locations
Identify by wetting the stone to reveal the 'six-sided' star pattern. Found most commonly on the shores of Lake Michigan and Lake Huron.
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