Rock Identifier
Petoskey Stone (Hexagonaria percarinata) — fossil
fossil

Petoskey Stone

Hexagonaria percarinata

AI-generated identification · may be incorrect

Hardness: 3.0-3.5 (Mohs scale), Color: Gray to tan when dry; reveals a distinctive six-sided coral pattern when wet, Luster: Dull to vitreous, Crystal structure: Hexagonal (calcified coral structure), Cleavage: None

Hardness
3
Color
Gray to tan when dry
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Physical properties

Hardness: 3.0-3.5 (Mohs scale), Color: Gray to tan when dry; reveals a distinctive six-sided coral pattern when wet, Luster: Dull to vitreous, Crystal structure: Hexagonal (calcified coral structure), Cleavage: None

Formation & geological history

Formed during the Devonian Period about 350 million years ago from the fossilized remains of ancient rugose coral colonies in warm, shallow seas.

Uses & applications

Used primarily for specimens, jewelry, paperweights, and decorative lapidary arts.

Geological facts

The Petoskey stone is the state rock of Michigan. Its unique pattern is formed by the individual coral polyps. The name comes from an Ottawa Chief, Pe-to-se-ga.

Field identification & locations

Identified by the unique 'hexagon' or honeycomb pattern visible on the surface, especially when wet or polished. Best found on the shores of Lake Michigan and Lake Huron.

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