sedimentary

Chalk or soft limestone fragment

Calcite-rich limestone; primarily calcium carbonate (CaCO₃)

AI-generated identification · may be incorrect

White to cream, dull and earthy, porous, and very soft (about Mohs 2–3); likely microcrystalline calcite with irregular fracture and no visible crystals. It should effervesce strongly with dilute hydrochloric acid or vinegar, though vinegar may react slowly.

Identified September 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms from accumulated microscopic marine shells and carbonate mud, later compacted and cemented into limestone; chalk commonly formed in Cretaceous marine seas, roughly 145–66 million years ago. The exact age cannot be determined from the image.

Uses & applications

Used in cement, lime, construction aggregate, soil treatment, paint, plastics, and as a filler; generally has negligible jewelry value.

Geological facts

Its pale color and powdery texture are characteristic of chalk, a particularly porous limestone. Some similar fragments may instead be weathered calcite-rich shell or soft limestone.

Field identification & locations

Common in marine sedimentary regions, including southern England, northern France, the U.S. Midwest, and parts of the Gulf and Mediterranean regions. Field identification: low hardness, white streak/powder, light weight, and acid fizz; avoid tasting or prolonged skin contact with unknown specimens.