sedimentary

Limestone

Calcium carbonate rock (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, gray, tan, or yellow; Luster: earthy to sub-vitreous; Crystal structure: microcrystalline or fine-grained calcite crystals; Cleavage: none, but breaks with a conchoidal to uneven fracture; Specific gravity: 2.7 to 2.9

Hardness: 3 on Mohs scale
Color: typically white, gray, tan, or yellow
Luster: earthy to sub-vitreous

Identified August 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed mainly through the accumulation of skeletal fragments of marine organisms such as coral, algal, and foraminifera, or through the chemical precipitation of calcium carbonate from water. Geologically ranges from Precambrian to recent times.

Uses & applications

Widely used in construction as building stone and crushed stone for road base, as an essential component in the manufacturing of Portland cement, in agriculture to neutralize acidic soils, and in metallurgy as a flux.

Geological facts

Limestone can host extensive cave systems due to its solubility in slightly acidic groundwater, leading to karstic topography. Famous monuments such as the Great Pyramid of Giza and parts of the Parthenon are built from limestone.

Field identification & locations

Easily identified in the field by reacting (effervescing) vigorously with dilute hydrochloric acid due to its carbonate composition. Found worldwide in sedimentary basins, ancient seabeds, and mountain ranges like the Alps and Rockies.