sedimentary

Chalky limestone

Micritic limestone, chiefly calcite (CaCO₃)

AI-generated identification · may be incorrect

Very soft (Mohs 2–3), pale cream to white, earthy/matte luster, fine-grained microcrystalline texture, and irregular fracture; may fizz vigorously with dilute hydrochloric acid. The surface appears porous and powdery, with possible fossil or shell impressions.

Identified August 28, 2026More sedimentary →

Explore Chalky limestone in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms from accumulated microscopic marine organisms, carbonate mud, or fragmented shells that compact and lithify in shallow seas. Its exact geological age cannot be determined from the image; chalky limestones range from Paleozoic to modern deposits.

Uses & applications

Used for cement and lime production, soil conditioning, aggregate, and building stone; attractive fossiliferous pieces are collected but generally have little gem value.

Geological facts

Calcite-rich limestone commonly preserves marine fossils and can be chemically dissolved to form caves and karst landscapes. Chalk is a particularly soft, porous variety of limestone formed largely from coccoliths.

Field identification & locations

Common worldwide, especially in former shallow-marine basins; notable deposits occur in England, France, the Mediterranean, and the central United States. Confirm with a vinegar or acid fizz test, low hardness, and a white streak; avoid confusing it with plaster or concrete.