Rock Identifier
Petoskey Stone / Fossilized Coral (Hexagonaria percarinata) — fossil
fossil

Petoskey Stone / Fossilized Coral

Hexagonaria percarinata

AI-generated identification · may be incorrect

Hardness of 3-4 on the Mohs scale, grayish-brown color, vitreous to dull luster, hexagonal corallite structures, specific gravity of approximately 2.6.

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Physical properties

Hardness of 3-4 on the Mohs scale, grayish-brown color, vitreous to dull luster, hexagonal corallite structures, specific gravity of approximately 2.6.

Formation & geological history

Formed through the fossilization of colonial rugose corals during the Devonian period, roughly 350 million years ago.

Uses & applications

Used primarily in lapidary arts, making decorative jewelry, and as a popular souvenir or collector specimen.

Geological facts

It is the official state stone of Michigan, named after the Odawa Native American Chief Pet-O-Sega.

Field identification & locations

Easily identified by the distinctive pattern of six-sided coral cells that appear when the stone is wet or polished, commonly found along beaches in the northern Lower Peninsula of Michigan.

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