sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, off-white, light brown; Luster: Dull to earthy; Crystal structure: Trigonal (calcite); Specific gravity: 2.5-2.7.

Hardness: 3 on Mohs scale
Color: Grey, off-white, light brown
Luster: Dull to earthy

Identified July 22, 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: Grey, off-white, light brown; Luster: Dull to earthy; Crystal structure: Trigonal (calcite); Specific gravity: 2.5-2.7.

Formation & geological history

Formed primarily in shallow, warm marine environments through the accumulation and compaction of organic debris such as shell fragments, coral, and micro-fossil skeletons, or by chemical precipitation of calcium carbonate from water over millions of years.

Uses & applications

Extensively used as crushed stone for road base and concrete aggregate, in cement manufacturing, soil stabilization in agriculture, and building stone.

Geological facts

Limestone accounts for about 10% of the total volume of all sedimentary rocks. Famous geological structures made of limestone include the White Cliffs of Dover and the landscape of the South China Karst.

Field identification & locations

Identified by its softness (can be scratched with a steel nail) and strong effervescence when exposed to dilute acid like vinegar or hydrochloric acid. Found abundantly worldwide in sedimentary basins.