sedimentary

Limestone

Calcium carbonate (CaCO3)

Hardness of 3 on the Mohs scale, color typically white, gray, or tan, dull to earthy luster, fine-grained to coarse-grained texture, and effervesces when exposed to dilute hydrochloric acid.

Identified July 29, 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

Hardness of 3 on the Mohs scale, color typically white, gray, or tan, dull to earthy luster, fine-grained to coarse-grained texture, and effervesces when exposed to dilute hydrochloric acid.

Formation & geological history

Formed through the accumulation of skeletal fragments of marine organisms such as coral, algal, and foraminifera, as well as the chemical precipitation of calcium carbonate from water in shallow marine environments.

Uses & applications

Widely used in construction as building stone and aggregate, in the production of lime and cement, as a soil conditioner in agriculture, and in various industrial chemical processes.

Geological facts

Limestone often preserves abundant marine fossils, providing geologists with a rich record of Earth's ancient oceans and climate history over hundreds of millions of years.

Field identification & locations

Easily identified by its reaction to acid (fizzing) and relatively soft texture. Commonly found in sedimentary basins, cliffs, and quarries worldwide.