sedimentary
Petoskey Stone
Hexagonaria percarinata
Hardness: 3.0-3.5 (Mohs), Color: Grey, tan, or brown with distinctive hexagonal coral patterns, Luster: Silky to vitreous when polished, Crystal structure: Hexagonal (Rugose coral), Specific gravity: 2.7
- Hardness
- 3
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Physical properties
Hardness: 3.0-3.5 (Mohs), Color: Grey, tan, or brown with distinctive hexagonal coral patterns, Luster: Silky to vitreous when polished, Crystal structure: Hexagonal (Rugose coral), Specific gravity: 2.7
Formation & geological history
Fossilized rugose coral formed during the Devonian period (approx. 350 million years ago) in shallow, warm tropical seas covering present-day Michigan. Glacial action later eroded and distributed the stones throughout the region.
Uses & applications
Commonly used in jewelry (pendants and rings), ornamental carvings, paperweights, and as a popular collector specimen.
Geological facts
It was named the state stone of Michigan in 1965. The name 'Petoskey' comes from the Ottawa Indian Chief Pet-O-Sega, meaning 'rising sun' or 'rays of hope'.
Field identification & locations
Identified by the unique six-sided 'sunburst' pattern on the surface. For best identification in the field, wet the stone to reveal the hidden patterns that are often difficult to see when dry. Primarily found on the shores of Lake Michigan and Lake Huron.
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