fossil

Polished fossil coral fragment

Fossilized colonial coral, commonly Favosites or related tabulate coral

AI-generated identification · may be incorrect

Cream, tan, brown, and gray pattern with a dark weathered rind; the visible cellular texture suggests coral corallites replaced by silica or calcite. Original calcitic coral is Mohs 3–4, while silicified material is about 6.5–7; luster is dull to waxy and structure is fossil cellular rather than crystalline.

Identified August 16, 2026More fossil →

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Physical properties

Formation & geological history

A Paleozoic colonial coral reef was buried in marine sediment and later mineralized during diagenesis, often by silica or carbonate. Exact age and identity require magnification of the corallite pattern and locality information.

Uses & applications

Primarily a display, teaching, and lapidary specimen; polished fossil coral is used for cabochons and ornamental objects, but is not generally a high-value gemstone.

Geological facts

Coral fossils preserve the skeletons of extinct reef-building animals, not plants. Silicified specimens can show cream, brown, and gray cellular mosaics when cut or polished.

Field identification & locations

Look for repeated tiny polygonal or tubular corallites, unlike random breccia or agate banding; a hand lens and hardness test help distinguish calcitic from silicified coral. Common in Paleozoic marine limestone deposits worldwide, including the Great Lakes region and western United States.