Rock Identifier
Petoskey Stone (Hexagonaria percarinata) — fossil
fossil

Petoskey Stone

Hexagonaria percarinata

AI-generated identification · may be incorrect

Hardness of 3 to 4 on the Mohs scale, mottled brown and tan color, dull to waxy luster, hexagonal corallite structure.

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Physical properties

Hardness of 3 to 4 on the Mohs scale, mottled brown and tan color, dull to waxy luster, hexagonal corallite structure.

Formation & geological history

Formed from fossilized rugose coral during the Devonian period, approximately 350 million years ago, in ancient tropical shallow seas.

Uses & applications

Popularly used in lapidary arts, decorative jewelry, and as a regional collectible souvenir.

Geological facts

It is the official state stone of Michigan and reveals distinct hexagonal patterns when wet or polished.

Field identification & locations

Easily identified by its characteristic pattern of six-sided coral cells; commonly found along the shores of Lake Michigan and northern lower peninsula gravel beds.

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