sedimentary

Chalky limestone

Micritic limestone, predominantly calcite (CaCO₃)

AI-generated identification · may be incorrect

Very pale white, dull to earthy luster, fine-grained and porous with a powdery texture; Mohs hardness 3, poor cleavage, and specific gravity about 2.3–2.7. It should effervesce strongly with dilute hydrochloric acid or vinegar.

Identified August 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms from compacted carbonate mud and microscopic marine-organism remains in shallow marine settings; individual pieces may range from recent deposits to hundreds of millions of years old. Common worldwide in Cretaceous and younger sedimentary basins.

Uses & applications

Used for cement and lime manufacture, soil neutralization, aggregate, fillers, and building stone; attractive dense varieties may be polished, though this specimen has little jewelry value.

Geological facts

Chalk is a soft, porous variety of limestone composed largely of coccolith microfossils, while denser white limestone can look similar. Its white streak and acid reaction help distinguish it from gypsum or quartz.

Field identification & locations

Common in England, France, the Mediterranean, the Gulf Coast, and many other former seafloors. Confirm with an acid test, powdery feel, and inability to scratch glass; avoid assuming exact identification from appearance alone.