Rock Identifier
Petoskey Stone (Hexagonaria percarinata) — fossil
fossil

Petoskey Stone

Hexagonaria percarinata

AI-generated identification · may be incorrect

Mohs hardness of 3; gray to brown color; exhibits a distinctive hexagonal coral pattern; massive crystal structure with calcite composition.

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Physical properties

Mohs hardness of 3; gray to brown color; exhibits a distinctive hexagonal coral pattern; massive crystal structure with calcite composition.

Formation & geological history

Formed from the fossilization of colonial rugose corals during the Devonian period, approximately 350 million years ago, in ancient shallow seas.

Uses & applications

Popularly used as a decorative stone, polished into cabochons for jewelry, and collected as a regional souvenir.

Geological facts

It is the official state stone of Michigan, named after the Ottawa Native American Chief Petosegay.

Field identification & locations

Easily identified by its unique honeycomb pattern of hexagonal corallites, typically found along the shores of Lake Michigan and northern Michigan gravel pits.

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