sedimentary

Fossiliferous limestone

Bioclastic carbonate rock, chiefly calcite (CaCO₃)

AI-generated identification · may be incorrect

Identified August 9, 2026More sedimentary →

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Physical properties

Gray to brown, fine- to medium-grained rock containing abundant shell or skeletal fragments; typically dull to slightly pearly, Mohs hardness about 3, and reacts vigorously with dilute hydrochloric acid. Calcite has trigonal crystal symmetry and perfect rhombohedral cleavage, though grains are commonly cemented and indistinct.

Formation & geological history

Forms from accumulated marine shells, crinoid debris, or other carbonate skeletons that are compacted and cemented on a shallow seafloor. Its age may range from Paleozoic to Cenozoic and cannot be determined from the photograph alone.

Uses & applications

Used as crushed aggregate, building stone, cement and lime feedstock, and occasionally as a decorative or fossil-collecting specimen; usually little jewelry value.

Geological facts

The visible curved and segmented patterns are consistent with fossil fragments, possibly brachiopods, mollusks, or crinoids, rather than metallic crystals.

Field identification & locations

Common in former shallow-marine sedimentary basins worldwide. Confirm by acid fizz, relatively easy scratching with a steel blade, and examining broken surfaces with a hand lens; avoid acid testing valuable specimens.