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 August 26, 2026More fossil →

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Physical properties

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.