sedimentary

Limestone

Calcareous sedimentary rock (CaCO3)

Hardness: 3 on the Mohs scale. Color: White, gray, tan, yellow, or brown. Luster: Earthy to dull. Crystal structure: Microcrystalline or fine-grained. Cleavage: None (has a conchoidal to uneven fracture). Specific Gravity: 2.7 to 2.9.

Hardness: 3 on the Mohs scale
Color: White, gray, tan, yellow, or brown
Luster: Earthy to dull

Identified August 4, 2026More sedimentary →

Explore Limestone in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed by the accumulation of skeletal fragments of marine organisms such as coral, algae, and molluscs, or through the chemical precipitation of calcium carbonate from water. Deposited in shallow, warm marine environments over millions of years.

Uses & applications

Widely used in construction as building stone, a major component of concrete, production of lime and cement, road base, soil conditioning in agriculture, and manufacturing of glass and paper.

Geological facts

Limestone is famous for forming dramatic landscapes called karst topography, featuring caves, sinkholes, and underground rivers. Famous structures like the Great Pyramid of Giza are largely constructed from limestone blocks.

Field identification & locations

Easily identified in the field by its characteristic reaction to dilute hydrochloric acid, which causes it to fizz or effervesce due to the release of carbon dioxide gas. Found worldwide in sedimentary basins and ancient sea beds.