sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.5-2.7

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

Identified February 19, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.5-2.7

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water. Often spans from the Paleozoic era to the present.

Uses & applications

Extensively used in construction as building stone and aggregate, road base, and raw material for cement. Also used in agriculture to neutralize soil acidity and in the chemical industry for glass making and air pollution control.

Geological facts

Limestone is the primary bedrock for cavern systems and karst topography. Approximately 10% of the total volume of all sedimentary rocks on Earth is limestone. It often contains abundant fossils of marine life.

Field identification & locations

Identify in the field by its characteristic gray color and the 'fizz test' (effervesces when exposed to dilute hydrochloric acid). Common in areas that were formerly ancient seabeds; often displays layering or bedding planes.