sedimentary

Weathered limestone cobble

Limestone, predominantly calcite (CaCO₃), possibly fossiliferous micrite

AI-generated identification · may be incorrect

Usually Mohs hardness 3, light gray to tan, dull to weakly earthy luster, fine-grained carbonate texture, and poor or indistinct cleavage. The rounded surface indicates abrasion and weathering; visible pale patches may be calcite or fossil material.

Identified August 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from compacted and cemented carbonate mud, shells, or microscopic marine organisms, commonly during Paleozoic–Mesozoic marine deposition, though the exact age cannot be determined visually. Later erosion produced the rounded cobble.

Uses & applications

Crushed limestone is used for aggregate, road base, cement, lime, and construction stone; attractive pieces may be collected, but this specimen has little gem or commercial value.

Geological facts

Limestone commonly effervesces vigorously with dilute hydrochloric acid or household vinegar if freshly scratched, because calcite releases carbon dioxide. Some varieties preserve abundant marine fossils.

Field identification & locations

Likely found in limestone-rich river gravel, glacial deposits, or quarry spoil; scratch-testing and acid reaction help distinguish it from sandstone or concrete. Common worldwide, especially in former shallow-sea regions.