sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture possible); Specific gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: Grey, white, or tan
Luster: Dull to earthy

Identified June 28, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture possible); Specific gravity: 2.5-2.7

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used primarily in construction for crushed stone, road base, and concrete aggregate. Also used in the production of cement, as a soil conditioner in agriculture, and for architectural cladding.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's caves are formed in limestone because it is soluble in weak acidic groundwater.

Field identification & locations

Identify in the field by its reaction (fizzing) when exposed to a drop of dilute hydrochloric acid. Commonly found in massive beds throughout the world's sedimentary basins.