fossil
Fossilized Coral (Petoskey Stone precursor)
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-4 (Calcite-based), Color: Tan, grey, or light brown with darker spots, Luster: Dull/Earthly when dry, Vitreous when wet, Crystal Structure: Hexagonal pattern of corallites
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Physical properties
Hardness: 3-4 (Calcite-based), Color: Tan, grey, or light brown with darker spots, Luster: Dull/Earthly when dry, Vitreous when wet, Crystal Structure: Hexagonal pattern of corallites
Formation & geological history
Formed during the Devonian period (approx. 350-400 million years ago) when warm, shallow seas covered much of North America; the coral was later buried by sediment and replaced by calcite and minerals.
Uses & applications
Collecting, decorative tumbled stones, jewelry making, and geological education.
Geological facts
This specimen shows the 'eye' pattern of the fossilized coral polyps. When polished or wet, the intricate hexagonal patterns common to Michigan's state stone, the Petoskey Stone, become highly visible.
Field identification & locations
Identified by the distinct circular or hexagonal 'spots' on the surface which represent individual coral organisms. Commonly found on beaches of the Great Lakes, especially Lake Michigan.
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