fossil

Petoskey Stone

Hexagonaria percarinata

AI-generated identification · may be incorrect

Hardness: 3-4 (calcite) to 7 (if silicified), Color: light brown to gray, Luster: dull to waxy when polished, Structure: fossilized coral displaying a hexagonal honeycomb pattern, Specific Gravity: 2.6-2.7

Identified August 25, 2026More fossil →

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Physical properties

Formation & geological history

Formed from the fossilization of Hexagonaria percarinata, a rugose coral that lived in shallow, tropical seas during the Devonian period, about 350 million years ago. Glaciers later dispersed these stones across Michigan.

Uses & applications

Popular as a lapidary material, often polished for jewelry, decorative items, and as a collectible state stone of Michigan.

Geological facts

The Petoskey stone is the official state stone of Michigan. The name comes from an Odawa Indian chief, Chief Pet-O-Sega, which translates to 'Sunbeams of Promise'.

Field identification & locations

Identifiable by the distinct hexagonal (six-sided) fossil pattern on its surface. Commonly found along the shores of Lake Michigan and Lake Huron, particularly near the town of Petoskey. Best spotted when wet, as the pattern stands out more clearly.