fossil

Fossilized shell fragment in limestone

Bioclast (likely bivalve or brachiopod) preserved in calcitic limestone

AI-generated identification · may be incorrect

Pale gray-beige, porous, dull to slightly pearly surface with visible shell growth structure and cemented mineral matrix; calcite hardness is about 3 Mohs, with rhombohedral cleavage and specific gravity near 2.7. Dilute hydrochloric acid should effervesce strongly on exposed matrix or shell.

Identified August 31, 2026More fossil →

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Physical properties

Formation & geological history

A marine shell was buried, mineral-filled, and lithified within carbonate sediment, commonly during the Paleozoic–Cenozoic; the exact age and organism cannot be determined from this image alone.

Uses & applications

Primarily a teaching, display, and collecting specimen; fossiliferous limestone is also used as aggregate, cement feedstock, and dimension stone.

Geological facts

The dark gray areas may be matrix, mineral staining, or a second fossil fragment rather than the original shell. Internal molds and shell cavities commonly become perforated during weathering.

Field identification & locations

Look for repeated shell ribs, concentric growth lines, bilateral symmetry, and carbonate reaction; common in marine limestone exposures worldwide. Avoid acid testing on valuable specimens and use a tiny inconspicuous spot.