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); Specific gravity: 2.5–2.7

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

Identified April 27, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

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

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 ocean or lake water.

Uses & applications

Extensively used in construction (concrete, road base), agriculture (soil conditioner), and as a chemical raw material for cement production and iron ore smelting.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in karst landscapes, leading to the formation of spectacular caves and sinkholes.

Field identification & locations

Identified in the field by its softness (can be scratched by a copper coin/knife) and vigorous effervescence (fizzing) when a drop of dilute hydrochloric acid is applied.