sedimentary

Fossiliferous limestone / shell hash rock

Bioclastic limestone (calcarenite or coquina), dominantly CaCO₃

AI-generated identification · may be incorrect

Dark, cemented carbonate matrix containing abundant shell and skeletal fragments, probably aragonite/calcite. Calcite hardness is 3, typically dull to granular, and should effervesce vigorously with dilute hydrochloric acid; fossils may be harder or silicified.

Identified September 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when marine shell debris accumulated in shallow, energetic water and was compacted and cemented by carbonate minerals. Its precise geological age cannot be determined from the photograph; such deposits range from Paleozoic to modern coastal settings.

Uses & applications

Used mainly as a teaching, display, and collecting specimen; similar limestone is used for aggregate, cement, lime, and building stone. Fossil-rich pieces have modest decorative and educational value.

Geological facts

Visible fragments include likely bivalve or gastropod shells and other marine debris, giving the rock a bioclastic texture. The black color may reflect organic matter, sulfides, weathering, or dark sedimentary matrix.

Field identification & locations

Common in shallow-marine limestone beds, shell banks, beaches, and quarry exposures. Confirm by acid reaction, visible shell microstructure, and lack of igneous crystals; locality information is needed for precise identification.