sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: Cream, white, or light gray; Luster: Dull to earthy; Structure: Fine-grained, microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.7

Hardness: 3 (Mohs scale)
Color: Cream, white, or light gray
Luster: Dull to earthy

Identified July 21, 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 (Mohs scale); Color: Cream, white, or light gray; Luster: Dull to earthy; Structure: Fine-grained, microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.7

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Primary source of lime for cement; used in road construction, building materials, agricultural soil treatment, and glass manufacturing.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most caves are formed by the dissolution of limestone by slightly acidic groundwater.

Field identification & locations

Can be identified in the field by its effervescence (fizzing) when exposed to a drop of diluted hydrochloric acid or strong vinegar. Commonly found in areas that were once prehistoric seafloors.