sedimentary

Chalky limestone

Micritic limestone, predominantly calcite (CaCO₃)

AI-generated identification · may be incorrect

White to pale gray, earthy/matte luster, fine-grained and porous, with tan iron-oxide staining; Mohs hardness 3, commonly effervesces strongly with dilute hydrochloric acid. It has no visible crystal structure, and cleavage is poor to absent; specific gravity is about 2.3–2.7.

Identified August 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from compacted carbonate mud and/or microscopic marine shells in a shallow marine environment, generally Cretaceous to younger in age. The broken surface and powdery texture are typical of chalk-rich limestone.

Uses & applications

Used for cement, lime, aggregate, soil amendment, and writing chalk; attractive pieces may be collected, but this specimen has little jewelry value.

Geological facts

Calcite-rich limestone can be distinguished from dolostone by a stronger cold-acid reaction. Tan coloration commonly results from oxidized iron minerals or weathering.

Field identification & locations

Common in marine sedimentary basins, including England, France, the Mediterranean, and many parts of North America. Identify it by its light color, softness, powdery texture, and vigorous acid fizz; avoid confusing it with plaster or concrete.