sedimentary

Limestone

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale); Color: White, gray, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71

Hardness: 3 (Mohs scale)
Color: White, gray, or tan
Luster: Dull to earthy

Identified June 2, 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: White, gray, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also be formed by the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as an aggregate, cement manufacturing, soil conditioner in agriculture, and as a decorative building stone.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Many world-famous caves and karst landscapes are formed by the dissolution of limestone by acidic rainwater.

Field identification & locations

Identified in the field by its softness (can be scratched by a copper coin) and its strong effervescent reaction when exposed to dilute hydrochloric acid. Commonly found in former marine basins.