sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, beige, or tan; Luster: Dull to earthy; Structure: Massive or layered; Cleavage: None; Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: Grey, beige, or tan
Luster: Dull to earthy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, beige, or tan; Luster: Dull to earthy; Structure: Massive or layered; Cleavage: None; Specific Gravity: 2.5-2.7

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also be precipitated from calcium-rich waters. Deposits can range from millions to hundreds of millions of years old.

Uses & applications

Primary source of lime for cement, used as a building stone (crushed or dimension stone), road base, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's caves are formed in limestone because it is soluble in weak acids (like rainwater).

Field identification & locations

Can be identified in the field by its reaction to cold dilute hydrochloric acid (it fizzes). Commonly found in areas that were once prehistoric seafloors. Look for fine-grained texture and occasional fossil inclusions.