fossil

Petoskey Stone

Hexagonaria percarinata

Hardness of 3 on the Mohs scale, colors ranging from greyish-brown to tan, dull to greasy luster, trigonal crystal system as calcite, specific gravity around 2.7.

Identified August 5, 2026More fossil →

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Physical properties

Hardness of 3 on the Mohs scale, colors ranging from greyish-brown to tan, dull to greasy luster, trigonal crystal system as calcite, specific gravity around 2.7.

Formation & geological history

Formed during the Devonian period about 350 million years ago through the fossilization of colonial rugose corals (Hexagonaria percarinata) in ancient warm seas.

Uses & applications

Used primarily in lapidary arts to create polished display stones, jewelry, decorative carvings, and as a popular souvenir.

Geological facts

It is the official state stone of Michigan, named after the Ottawa Native American Chief Pet-O-Sega. The distinctive pattern resembles sunbursts or hexagons.

Field identification & locations

Easily identified by the distinctive pattern of six-sided coral corallites visible on the surface. Commonly found along beaches and glacial drift in the northern lower peninsula of Michigan.