sedimentary

Limestone

Calcium Carbonate (CaCO3)

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

Identified March 20, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically white, gray, 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 be formed by the chemical precipitation of calcium carbonate from lake or ocean water. Most deposits range from the Paleozoic to Cenozoic eras.

Uses & applications

Extensively used in construction as an aggregate for concrete and asphalt, as a building stone, and in the production of cement and lime. It is also used in agriculture to neutralize soil acidity and in the chemical industry for glass making.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. The Great Pyramids of Giza were originally encased in polished white limestone, and most of the world's most famous caves, such as Mammoth Cave, are formed within limestone layers.

Field identification & locations

Can be identified in the field by its softness (it can be scratched by a copper coin or steel knife) and its strong 'fizzing' reaction when exposed to cold dilute hydrochloric acid. It often contains visible fossils of marine organisms. Commonly found in areas that were once prehistoric seafloors.