sedimentary

Limestone

Calcium carbonate (CaCO3) / Limestone

Hardness: 3 on Mohs scale; Color: Tan, beige, off-white to yellowish-brown; Luster: Dull to earthy; Texture: Fine-grained, porous, microcrystalline matrix; Specific Gravity: 2.5-2.7.

Hardness: 3 on Mohs scale
Color: Tan, beige, off-white to yellowish-brown
Luster: Dull to earthy

Identified July 25, 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: 3 on Mohs scale; Color: Tan, beige, off-white to yellowish-brown; Luster: Dull to earthy; Texture: Fine-grained, porous, microcrystalline matrix; Specific Gravity: 2.5-2.7.

Formation & geological history

Formed primarily in shallow, warm marine environments by the accumulation and compaction of organic debris such as shell fragments, coral, and calcium carbonate precipitates over millions of years.

Uses & applications

Widely used in construction as building stone, crushed aggregate for concrete and roads, manufacture of cement, soil conditioner in agriculture, and neutralizer in chemical processes.

Geological facts

Limestone reacts strongly with dilute hydrochloric acid, producing carbon dioxide gas bubbles (effervescence), which is the primary field test used by geologists to identify it.

Field identification & locations

Can be identified in the field by its light tan/grey color, soft surface that can be scratched by steel, earthy texture, and effervescent reaction to acid. Commonly found in karst landscapes, quarries, and exposed sedimentary rock layers worldwide.