Rock Identifier
Fossil Coral (Rugosa or Tabulata coral fossil) — fossil
fossil

Fossil Coral

Rugosa or Tabulata coral fossil

AI-generated identification · may be incorrect

Hardness 3-4 on Mohs scale, typically brown, grey, or tan with a dull to vitreous luster. Features distinct honeycomb or star-like hexagonal corallite structures.

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Physical properties

Hardness 3-4 on Mohs scale, typically brown, grey, or tan with a dull to vitreous luster. Features distinct honeycomb or star-like hexagonal corallite structures.

Formation & geological history

Formed through the process of permineralization, where ancient coral skeletons from the Paleozoic era are replaced by silica or calcite over hundreds of millions of years.

Uses & applications

Used primarily in lapidary arts, wire-wrapped jewelry, decorative display pieces, and as educational teaching specimens for fossil collectors.

Geological facts

Many fossil coral specimens, particularly Petoskey stones, are state stones and record ancient tropical reef environments that existed before the dinosaurs.

Field identification & locations

Identify by distinctive honeycomb patterns or internal tubule structures exposed on weathered surfaces. Commonly found in sedimentary limestone layers worldwide.

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Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

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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
Fossil oyster shell (Oyster (family Ostreidae); shell composed chiefly of calcite (CaCO₃)) — fossil

Fossil oyster shell

Oyster (family Ostreidae); shell composed chiefly of calcite (CaCO₃)

fossil