Rock Identifier
Fossilized Coral (Rugosa / Scleractinia (silicified or calcified coral)) — fossil
fossil

Fossilized Coral

Rugosa / Scleractinia (silicified or calcified coral)

AI-generated identification · may be incorrect

Mohs hardness of 3-4 (if calcite) or 6.5-7 (if replaced by quartz); colors range from grey to brown and tan; dull to waxy luster; variable crystal structure depending on mineral replacement.

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Physical properties

Mohs hardness of 3-4 (if calcite) or 6.5-7 (if replaced by quartz); colors range from grey to brown and tan; dull to waxy luster; variable crystal structure depending on mineral replacement.

Formation & geological history

Formed in ancient shallow marine environments where coral skeletons were buried in sediment and replaced by minerals over millions of years.

Uses & applications

Used primarily in lapidary arts for cabochons, jewelry, and ornamental carvings, as well as valued by fossil collectors.

Geological facts

Fossil coral is the state gemstone of Michigan and Florida. It provides valuable data regarding ancient ocean temperatures and prehistoric marine ecosystems.

Field identification & locations

Look for distinctive honeycomb or star-shaped cellular patterns on the weathered surface. Commonly found in sedimentary limestone deposits worldwide.

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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
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