Rock Identifier
Fossil Coral (Hexagonaria (Rugose coral) / Calcium Carbonate (CaCO3)) — fossil
fossil

Fossil Coral

Hexagonaria (Rugose coral) / Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness of 3-4 on the Mohs scale, grayish to brownish color, dull to vitreous luster, hexagonal or honeycomb crystal structure with distinct corallite patterns.

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Physical properties

Hardness of 3-4 on the Mohs scale, grayish to brownish color, dull to vitreous luster, hexagonal or honeycomb crystal structure with distinct corallite patterns.

Formation & geological history

Formed through the fossilization of ancient marine corals in shallow tropical seas during the Paleozoic era, particularly the Devonian period.

Uses & applications

Used primarily in lapidary work, cabochons, decorative carvings, and as a popular specimen for fossil collectors.

Geological facts

Petoskey stone, a famous type of fossil coral, is the official state stone of Michigan. The honeycomb patterns represent individual coral polyps.

Field identification & locations

Easily identified by its distinctive hexagonal cellular pattern on weathered limestone surfaces; found globally in ancient sedimentary marine deposits.

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Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

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Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

fossil