Rock Identifier
Petoskey Stone (Hexagonaria percarinata) — fossil
fossil

Petoskey Stone

Hexagonaria percarinata

AI-generated identification · may be incorrect

Hardness of 3 on Mohs scale, brownish-gray color when dry and patterned with hexagonal corallite structures, dull to sub-vitreous luster, specific gravity around 2.6-2.7.

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Physical properties

Hardness of 3 on Mohs scale, brownish-gray color when dry and patterned with hexagonal corallite structures, dull to sub-vitreous luster, specific gravity around 2.6-2.7.

Formation & geological history

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

Uses & applications

Popularly used for lapidary work, decorative objects, polished cabochons, and as the official state stone of Michigan.

Geological facts

When wet or polished, the distinct honeycomb coral pattern becomes vividly clear, revealing the ancient coral structures. Glacial action helped distribute these stones across northern Michigan.

Field identification & locations

Easily identified in the field by its characteristic six-sided corallite pattern resembling a honeycomb. Commonly found along the shores of Lake Michigan and Lake Huron.

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