sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically light gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.5 to 2.7.

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

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically light gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.5 to 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. Found in geological formations ranging from the Precambrian to Holocene.

Uses & applications

Extensively used in construction for aggregate, cement production, and building stone. Also used as a soil conditioner in agriculture and as a raw material in the glass and chemical industries.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's great caves, including Mammoth Cave in Kentucky, are formed by the dissolution of limestone by acidic groundwater.

Field identification & locations

Identify in the field by its reaction to dilute hydrochloric acid (it will effervesce or fizz). It often contains visible fossils. Common in areas that were once prehistoric sea beds.