Rock Identifier
Fossil Coral (Hexagonaria (Rugosa coral)) — fossil
fossil

Fossil Coral

Hexagonaria (Rugosa coral)

AI-generated identification · may be incorrect

Hardness of 3 to 4 on the Mohs scale with white, grey, or tan coloration and a dull to vitreous luster. Features distinctive honeycomb or star-shaped calices.

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Physical properties

Hardness of 3 to 4 on the Mohs scale with white, grey, or tan coloration and a dull to vitreous luster. Features distinctive honeycomb or star-shaped calices.

Formation & geological history

Formed from ancient coral reefs during the Paleozoic era, particularly the Devonian period, through the process of permineralization where silica or calcite replaces the original coral skeleton.

Uses & applications

Used primarily in lapidary arts for cabochons, jewelry, and ornamental carvings, as well as valued by fossil collectors.

Geological facts

Also known as Petoskey stone, this fossil is the state stone of Michigan and reveals ancient tropical seas that covered North America hundreds of millions of years ago.

Field identification & locations

Easily identified by its characteristic polygonal coral structures and mottled patterns, commonly found in limestone-rich quarries and glacial drift.

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