Rock Identifier
Polished fossil coral (Fossilized colonial coral, commonly tabulate or rugose coral; calcite (CaCO₃) replacement) — fossil
fossil

Polished fossil coral

Fossilized colonial coral, commonly tabulate or rugose coral; calcite (CaCO₃) replacement

AI-generated identification · may be incorrect

Brown to gray polished surface with radiating, branching coralite patterns and pale mineral infill; calcite hardness 3, vitreous to waxy luster, low relief, and no obvious cleavage. The rounded shape appears tumbled or naturally water-worn.

Identified More fossil →
Explore Polished fossil coral in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App StoreGoogle Play

Physical properties

Brown to gray polished surface with radiating, branching coralite patterns and pale mineral infill; calcite hardness 3, vitreous to waxy luster, low relief, and no obvious cleavage. The rounded shape appears tumbled or naturally water-worn.

Formation & geological history

A Paleozoic coral colony was buried in marine sediment and progressively mineralized, commonly during the Devonian–Permian (about 419–252 million years ago). Silica, calcite, or iron-bearing fluids can produce the brown coloration and white vein-like structures.

Uses & applications

Used as a decorative gemstone, cabochon, paperweight, and educational fossil specimen; not generally used as structural stone. Value depends on pattern, polish, size, and confirmed locality.

Geological facts

The apparent “branches” are coral corallites and growth structures, not crystal veins; white areas may be calcite infilling or weathered replacement. Acid can weakly fizz on exposed calcite surfaces.

Field identification & locations

Identify by repeating biological corallite patterns, unlike random mineral veining; test cautiously with a steel point and dilute acid on an inconspicuous spot. Common examples come from Morocco, Madagascar, Indonesia, and the U.S. Midwest.

More like this

Other fossil specimens

Probable fossil-bearing rock or mineral concretion (Unidentified carbonate-rich concretion with a possible fossil inclusion) — fossil

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

fossil
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