Rock Identifier
Petoskey Stone (Hexagonaria percarinata) — fossil
fossil

Petoskey Stone

Hexagonaria percarinata

AI-generated identification · may be incorrect

Hardness of 3 on the Mohs scale, brownish-gray color when dry, dull to greasy luster, hexagonal coral corallites visible, specific gravity around 2.6.

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Physical properties

Hardness of 3 on the Mohs scale, brownish-gray color when dry, dull to greasy luster, hexagonal coral corallites visible, specific gravity around 2.6.

Formation & geological history

Formed from fossilized rugose coral during the Devonian period about 350 million years ago in ancient shallow seas of Michigan.

Uses & applications

Popularly used for decorative ornamental objects, cabochons, polished display pieces, and jewelry making.

Geological facts

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

Field identification & locations

Easily identified by the distinctive pattern of six-sided coral cells that appear uniquely mottled when wet; found heavily along the shores of northern Lake Michigan.

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