Rock Identifier
Fossil Coral (Rugosa or Tabulata coral fossil (Calcium Carbonate, CaCO3)) — fossil
fossil

Fossil Coral

Rugosa or Tabulata coral fossil (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness of 3-4 on the Mohs scale, earthy to vitreous luster, displays distinctive internal honeycomb or star-shaped corallite structures, specific gravity around 2.7.

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Physical properties

Hardness of 3-4 on the Mohs scale, earthy to vitreous luster, displays distinctive internal honeycomb or star-shaped corallite structures, specific gravity around 2.7.

Formation & geological history

Formed through the process of permineralization or silicification, where ancient coral skeletons from warm Paleozoic shallow seas (hundreds of millions of years ago) are replaced by minerals.

Uses & applications

Used primarily as decorative lapidary material, in polished cabochons for jewelry, and as a prized specimen for fossil collectors.

Geological facts

Many fossil corals are preserved as agate or chalcedony after ancient silica-rich groundwater replaced the original calcite skeleton.

Field identification & locations

Identify in the field by searching sedimentary limestone formations for distinctive geometric tube or honeycomb patterns; common worldwide including in the US Midwest.

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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) — fossil

Likely fossil oyster shell

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

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

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil
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