fossil

Fossil coral limestone

Fossilized colonial coral, commonly tabulate or rugose coral in calcite-rich limestone (CaCO₃)

AI-generated identification · may be incorrect

Typically gray to tan, with repeating polygonal or circular corallite chambers; dull to waxy luster, massive structure, and Mohs hardness about 3–4. Calcite may show weak cleavage and fizzes with dilute hydrochloric acid.

Identified August 16, 2026More fossil →

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Physical properties

Formation & geological history

A colonial coral reef was buried in marine sediment, then mineralized and lithified into limestone; specimens commonly date from Paleozoic–Mesozoic seas, roughly 250–450 million years old. The rounded form appears naturally weathered or possibly tumbled/polished.

Uses & applications

Primarily a collectible and educational fossil; cut pieces are used decoratively, while fossil-bearing limestone can serve as aggregate or dimension stone. Not generally used as gemstone jewelry.

Geological facts

The circular patterns are individual corallites—spaces once occupied by coral polyps—not ordinary mineral crystals. Internal walls and septa can help distinguish coral from orbicular jasper or vesicular igneous rock.

Field identification & locations

Identify it by its consistent biological honeycomb pattern, irregular natural chambers, carbonate composition, and acid reaction; common sources include limestone beds in North America, Europe, and Australia. Typical value is about $10–$50 for a small common specimen, or $50–$200+ if large, attractive, and well preserved.