sedimentary

Polished fossiliferous limestone

Bioclastic limestone, commonly crinoidal or shell-rich micrite

AI-generated identification · may be incorrect

Dark gray to black, smoothly tumbled or polished, with abundant pale fossil fragments and cavities. Calcite-rich; Mohs hardness 3, dull to waxy luster, generally massive with no cleavage visible; reacts readily with dilute hydrochloric acid.

Identified September 11, 2026More sedimentary →

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Physical properties

Formation & geological history

A marine carbonate sediment formed from accumulated shells, skeletal debris, or microfossils that lithified and later became dark through organic matter or alteration. Its exact geological age cannot be determined from the image; such limestones range from Paleozoic to Cenozoic.

Uses & applications

Used as decorative stone, polished specimens, cabochons, and educational fossils; limestone is also widely used for cement, aggregate, and building stone.

Geological facts

The light inclusions are fossil or skeletal fragments rather than crystals. A polished surface can obscure bedding, but fossil shapes and acid effervescence are diagnostic.

Field identification & locations

Common in ancient shallow-marine limestone districts worldwide, including the UK, Europe, North America, and Morocco. Identify by its strong acid fizz, relatively low hardness, and visible bioclasts; avoid vinegar for subtle testing or use a concealed spot.