sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, tan, brownish, white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral (in crystalline calcite forms)

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

Identified July 25, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, tan, brownish, white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral (in crystalline calcite forms)

Formation & geological history

Formed primarily in shallow, warm marine environments from the accumulation and compaction of organic debris such as shell fragments, coral, and microfossils, or through direct chemical precipitation of calcium carbonate.

Uses & applications

Extensively used as aggregate in construction, production of cement and lime, soil conditioner in agriculture, architectural stone, and raw material in chemical manufacturing.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Karst landscapes, famous for caves, sinkholes, and underground rivers, are formed by the dissolution of limestone by acid rainwater.

Field identification & locations

Easily identified in the field by testing with dilute hydrochloric acid, which causes it to effervesce (fizz) vigorously. It is widely distributed worldwide in ancient sedimentary basins.