Rock Identifier
Coral Skeleton / Fossil Coral (Scleractinia (Aragonite, CaCO3)) — fossil
fossil

Coral Skeleton / Fossil Coral

Scleractinia (Aragonite, CaCO3)

AI-generated identification · may be incorrect

Hardness around 3 to 4 on Mohs scale. Color ranges from off-white to pale cream or gray. Luster is dull to earthy. Highly porous, honeycomb-like or pitted structure composed of calcium carbonate (aragonite or calcite).

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Physical properties

Hardness around 3 to 4 on Mohs scale. Color ranges from off-white to pale cream or gray. Luster is dull to earthy. Highly porous, honeycomb-like or pitted structure composed of calcium carbonate (aragonite or calcite).

Formation & geological history

Formed by marine invertebrate animals (coral polyps) that secrete calcium carbonate skeletons in warm, shallow ocean environments. Can range from modern beach-drifted skeletal fragments to ancient fossilized coral reefs millions of years old.

Uses & applications

Used in aquarium decoration, jewelry (when mineralized or polished), souvenirs, educational collections, and as an indicator of ancient marine environments in geology.

Geological facts

Over geological time, aragonite in coral skeletons often recrystallizes into the more stable mineral calcite, turning ancient corals into solid limestone fossils such as Petoskey stone.

Field identification & locations

Identified by tiny repeating pores, corallites, or star-like cell patterns across the surface. Commonly found washed up on tropical beaches, marine terraces, or in limestone formations worldwide.

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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
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Rounded sedimentary pebble

Likely micritic limestone or calcareous sandstone

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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