sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Off-white, beige, or grey; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite particles; Specific gravity: 2.3 to 2.7.

Hardness: 3 on Mohs scale
Color: Off-white, beige, or grey
Luster: Dull to earthy

Identified May 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form through chemical precipitation from calcium-rich water. It occurs in extensive layers across all geological ages, notably the Paleozoic and Mesozoic eras.

Uses & applications

Widely used in construction as building stone, road base, and a key ingredient in cement/concrete. Also used as a soil conditioner in agriculture and to neutralize acid in industrial processes.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. The Great Pyramids of Giza are largely constructed from limestone blocks.

Field identification & locations

Identify in the field by its soft surface (can be scratched by a steel nail) and its vigorous reaction (fizzing) when exposed to a drop of dilute hydrochloric acid or vinegar. Often found in karst landscapes with caves and sinkholes.