sedimentary

Limestone Concretion (Botryoidal/Calcareous Nodules)

Calcium Carbonate Concretion (CaCO3)

Hardness around 3-4 on Mohs scale; light tan, brownish-grey color with dark weathering crusts; dull to earthy luster; irregular, rounded, or botryoidal nodular texture; reacts vigorously with dilute hydrochloric acid.

Identified July 24, 2026More sedimentary →

Explore Limestone Concretion (Botryoidal/Calcareous Nodules) in the encyclopedia →

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Physical properties

Formation & geological history

Formed by the precipitation of mineral cement within the spaces between particles in sedimentary beds (typically limestone, shale, or sandstone) during diagenesis, often around an organic nucleus.

Uses & applications

Mainly collected as geological curiosities or novelty rock specimens; larger deposits of host limestone are used in construction, cement manufacturing, and agricultural soil conditioning.

Geological facts

Concretions are often mistaken for fossils, meteorites, or petrified wood due to their unusual, rounded, or lumpy shapes. They can grow to sizes ranging from a few millimeters to several meters across.

Field identification & locations

Identify by its irregular, knobby structure, relatively light weight compared to iron meteorites, and strong fizz reaction when tested with acid. Commonly found in sedimentary rock outcrops, stream beds, and limestone quarries.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Shale

Shale (clastic sedimentary rock)

sedimentary

Shale

Argillaceous sedimentary rock

sedimentary

Mudstone

Argillite / Siliciclastic sedimentary rock

sedimentary