fossil

Fossilized Coral (Petoskey Stone / Charlevoix Stone type)

Hexagonaria percarinata (or similar Favositidae/Rugosa coral)

AI-generated identification · may be incorrect

Hardness: ~3 on Mohs scale (calcite). Color: typically gray, brown, tan, with intricate hexagonal or honeycomb patterns. Luster: dull to waxy (can be polished).

Hardness: ~3 on Mohs scale (calcite)
Luster: dull to waxy (can be polished)

Identified August 25, 2026More fossil →

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Physical properties

Hardness: ~3 on Mohs scale (calcite). Color: typically gray, brown, tan, with intricate hexagonal or honeycomb patterns. Luster: dull to waxy (can be polished).

Formation & geological history

Formed during the Devonian period (roughly 350 million years ago) in shallow tropical seas. The coral skeleton was fossilized and replaced by calcite or silica.

Uses & applications

Commonly collected as a souvenir, polished for jewelry (cabochons), or used in small carvings.

Geological facts

The Petoskey stone is the state stone of Michigan. The pattern is created by the fossilized remains of rugose coral polyps.

Field identification & locations

Identified by the distinct hexagonal or honeycomb pattern, especially visible when wet. Commonly found along the shores of the Great Lakes (especially Lake Michigan).