sedimentary

White limestone or chalky carbonate rock

Calcite-rich limestone; possibly chalk (CaCO₃)

AI-generated identification · may be incorrect

Soft, white to pale gray, dull and fine-grained with irregular fracture; calcite hardness Mohs 3, nonmetallic luster, no visible crystals or cleavage. It should fizz vigorously with dilute hydrochloric acid or vinegar, though vinegar may react slowly.

Identified August 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from accumulated marine carbonate mud, shells, or microscopic organisms; age cannot be determined from the image and may range from Paleozoic to Cenozoic. Chalk is a porous, soft variety of limestone.

Uses & applications

Used for cement, lime, aggregate, soil neutralization, and building stone; attractive pieces may be collected but generally have little commercial value.

Geological facts

Calcite is commonly the dominant mineral, and the white color reflects high carbonate purity with little iron or organic matter.

Field identification & locations

Common in sedimentary terrains, quarries, coastal cliffs, and stream gravels worldwide; distinguish it from quartz by its softness and acid reaction, and from gypsum by its stronger fizz. Estimated value: $1–$10 for a loose common specimen, or $10–$30 if fossiliferous or unusually aesthetic.