fossil

Coral limestone / fossil coral

Biogenic calcium carbonate, chiefly aragonite or calcite (CaCO₃); likely fossilized colonial coral

AI-generated identification · may be incorrect

Light cream to gray, highly porous, dull to chalky luster, irregular honeycomb-like corallite cavities; Mohs hardness about 3–4, with no consistent cleavage. Low density and reacts vigorously with dilute hydrochloric acid or vinegar.

Identified August 7, 2026More fossil →

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Physical properties

Formation & geological history

Formed from coral colonies in warm, shallow marine environments, later lithified or mineral-replaced during burial and uplift. Exact geological age cannot be determined from the photograph; specimens may range from Paleozoic to Quaternary.

Uses & applications

Used as a collectible fossil, educational specimen, aquarium decoration, and occasionally crushed for lime or aggregate; it is generally unsuitable for fine jewelry.

Geological facts

The repeated pores are coral corallites, not vesicles from volcanic lava. Mineral replacement commonly preserves the original coral architecture while changing aragonite to calcite.

Field identification & locations

Identify by its branching or honeycomb coral pattern, carbonate reaction, and marine-fossil texture; distinguish it from pumice, which is glassy and volcanic. Common in uplifted tropical reef limestones worldwide, including Florida, the Caribbean, Australia, and Pacific islands.