sedimentary

Weathered limestone cobble

Limestone, predominantly calcite (CaCO₃)

AI-generated identification · may be incorrect

Usually Mohs hardness 3, pale gray to buff, dull to faintly crystalline luster, and massive texture with no obvious cleavage in the whole cobble; may fizz with dilute hydrochloric acid or vinegar. The rounded shape indicates water or glacial abrasion, while the pale patches may be weathering or fossil fragments.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from compacted and cemented carbonate mud, shells, or skeletal debris in a shallow marine environment, commonly during Paleozoic–Mesozoic time; exact age cannot be determined from the image. Its rounded form likely developed in a stream, beach, or glacial deposit.

Uses & applications

Used for crushed aggregate, cement and lime manufacture, building stone, and landscaping; attractive fossiliferous pieces may be collected, though this specimen appears common and unpolished.

Geological facts

Limestone dissolves relatively easily in weak acids, producing carbon dioxide bubbles, and commonly develops caves and karst landscapes.

Field identification & locations

Likely limestone if it fizzes strongly and is soft enough to scratch with a steel knife; dolostone is a possibility if it reacts weakly. Common worldwide, especially in former marine basins and glacial or river gravels.