Rock Identifier
Petoskey Stone (Favosites alpenensis) — fossil
fossil

Petoskey Stone

Favosites alpenensis

AI-generated identification · may be incorrect

Hardness of 3-4 on Mohs scale, grey to brown color when dry, vitreous to dull luster, hexagonal corallite structure.

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Physical properties

Hardness of 3-4 on Mohs scale, grey to brown color when dry, vitreous to dull luster, hexagonal corallite structure.

Formation & geological history

Formed from fossilized colonial rugose or tabulate corals during the Devonian period, approximately 350 million years ago in ancient tropical seas.

Uses & applications

Used primarily for lapidary work, decorative objects, and as a regional souvenir or jewelry stone in Michigan.

Geological facts

It is the official state stone of Michigan, named after an Ottawa Native American chief named Pet-O-Sega.

Field identification & locations

Easily identified by the distinctive hexagonal honeycomb pattern visible on the surface, especially when wet or polished; found abundantly in glacial drift and along shores in northern Michigan.

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