sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically gray, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: typically gray, white, or tan
Luster: dull to earthy

Identified March 17, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically gray, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.71

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Can also form through the precipitation of calcium carbonate from lake or ocean water. It can range in age from the Precambrian to recent formations.

Uses & applications

Extensively used in construction as an aggregate for road base and railroad ballast, a component in cement and mortar, a soil conditioner in agriculture, and as a raw material for the chemical industry. Higher grade varieties are used for sculpture and architecture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in 'Karst' topography, where its solubility in weakly acidic water creates spectacular caves and sinkholes.

Field identification & locations

Identify in the field by its light color, presence of fossils, and its reaction (fizzing) when a drop of diluted hydrochloric acid or strong vinegar is applied. It is ubiquitous in sedimentary basins worldwide.