sedimentary

Weathered limestone or calcareous concretion

Calcite-rich carbonate rock; chiefly calcium carbonate (CaCO₃)

AI-generated identification · may be incorrect

Tan-brown, dull to earthy luster, fine-grained and irregularly fractured; likely Mohs hardness 3, with low-to-moderate density. Calcite commonly shows rhombohedral cleavage, though weathering obscures it.

Identified September 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed as limestone sediment or a carbonate-rich concretion that lithified in a marine, freshwater, or soil environment; its exact geological age cannot be determined from the photograph.

Uses & applications

Used as aggregate, cement and lime feedstock, building stone, and soil neutralizer; this rough specimen has little jewelry or commercial value.

Geological facts

A drop of dilute hydrochloric acid or strong vinegar should produce visible fizz if calcite-rich, although weathered surfaces may react weakly. Brown coloration commonly comes from iron-oxide staining or clay.

Field identification & locations

Common in sedimentary terrains worldwide, including caves, streambeds, and construction exposures. Confirm with acid fizz, relatively low hardness, and a white streak; avoid confusing it with cement or porous slag.