Rock Identifier
Fossil coral limestone (Fossilized colonial coral, commonly tabulate or rugose coral, preserved in calcite (CaCO₃)) — fossil
fossil

Fossil coral limestone

Fossilized colonial coral, commonly tabulate or rugose coral, preserved in calcite (CaCO₃)

AI-generated identification · may be incorrect

Typically gray-brown, fine-grained, and dull to slightly waxy, with repeated circular corallite structures; calcite hardness is about 3, with poor cleavage and specific gravity near 2.7. The visible polygonal or round cups are coral fossils rather than mineral crystals.

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Physical properties

Typically gray-brown, fine-grained, and dull to slightly waxy, with repeated circular corallite structures; calcite hardness is about 3, with poor cleavage and specific gravity near 2.7. The visible polygonal or round cups are coral fossils rather than mineral crystals.

Formation & geological history

A Paleozoic or younger marine coral colony was buried and lithified as carbonate sediment, then mineralized by calcite; exact age requires locality and microscopy. It commonly forms fossiliferous limestone in ancient shallow tropical seas.

Uses & applications

Used as a collector specimen, educational material, and occasionally as decorative stone; it is generally unsuitable for jewelry unless polished and stable.

Geological facts

Coral fossils preserve the individual corallites—the skeletal chambers of a colony—and can resemble orbicular textures at a glance.

Field identification & locations

Identify it by repeated corallite cups or honeycomb patterns, carbonate reaction with dilute hydrochloric acid, and lack of glassy crystal faces. Common in Paleozoic limestone deposits worldwide, including the United States, Morocco, Madagascar, and Australia.

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