Rock Identifier
Fossil Coral (Rugosa or Tabulata coral fossilized in Agate/Chalcedony) — fossil
fossil

Fossil Coral

Rugosa or Tabulata coral fossilized in Agate/Chalcedony

AI-generated identification · may be incorrect

Hardness of 6.5-7 on the Mohs scale, exhibits earthy to waxy luster, brown and tan coloration with distinctive starburst or honeycomb cellular structures, specific gravity of 2.6-2.7.

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Physical properties

Hardness of 6.5-7 on the Mohs scale, exhibits earthy to waxy luster, brown and tan coloration with distinctive starburst or honeycomb cellular structures, specific gravity of 2.6-2.7.

Formation & geological history

Formed when ancient coral skeletons in shallow warm seas were replaced by silica-rich groundwater over hundreds of millions of years during the Paleozoic era.

Uses & applications

Used primarily in lapidary arts, cabochons for jewelry, and as collectible paleontological specimens.

Geological facts

Fossil coral is the state stone of Michigan, where Petoskey stones represent a specific type of fossilized colonial coral from the Devonian period.

Field identification & locations

Identifiable by its distinct pattern of tiny star-like corallites embedded in a microcrystalline quartz matrix. Found globally in ancient marine sedimentary 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
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