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 and patterned when wet, vitreous to dull luster, hexagonal corallite structure.

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Physical properties

Hardness of 3 on the Mohs scale, brownish-gray color when dry and patterned when wet, vitreous to dull luster, hexagonal corallite structure.

Formation & geological history

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

Uses & applications

Used primarily in lapidary arts for ornamental objects, polished display stones, and custom jewelry.

Geological facts

It is the official state stone of Michigan and reveals distinct mosaic patterns of six-sided coral cells when wet or polished.

Field identification & locations

Easily identified by its characteristic pattern of contiguous hexagonal shapes, commonly found along beaches and glacial deposits in the northern lower peninsula of Michigan.

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