sedimentary

Limestone

Calcium carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: tan, buff, light brown; Luster: dull, earthy; Texture: fine-grained, microcrystalline to clastic; Cleavage: none (conchoidal to uneven fracture).

Hardness: 3 on Mohs scale
Color: tan, buff, light brown
Luster: dull, earthy

Identified July 25, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: tan, buff, light brown; Luster: dull, earthy; Texture: fine-grained, microcrystalline to clastic; Cleavage: none (conchoidal to uneven fracture).

Formation & geological history

Formed primarily in shallow, warm marine environments through the accumulation and compaction of organic debris such as shell fragments, coral, and algal remains, or via chemical precipitation of calcium carbonate.

Uses & applications

Widely used as a construction material, in crushed stone for road bases, as a key component in cement production, and for soil acidity neutralisation in agriculture.

Geological facts

Limestone is highly susceptible to weathering by acidic rainwater, which dissolves the rock over time to create dramatic karst landscapes, including sinkholes, caves, and underground rivers.

Field identification & locations

Identifiable in the field by its soft nature (can be scratched by a steel nail), dull earthy appearance, and a vigorous effervescent reaction when exposed to dilute hydrochloric acid. Commonly found worldwide in ancient sea beds and sedimentary basins.