sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Structure: non-crystalline to massive; Cleavage: none; Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: typically white, gray, or tan
Luster: dull to earthy

Identified May 31, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Structure: non-crystalline to massive; Cleavage: none; Specific Gravity: 2.5-2.7

Formation & geological history

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

Uses & applications

Used extensively in construction as road base, railroad ballast, and concrete aggregate. Also used in the production of cement, for soil neutralization in agriculture, and as a feedstock for lime.

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 easily dissolved by acidic groundwater.

Field identification & locations

Can be identified in the field by its softness (it can be scratched by a copper coin) and its effervescence (bubbling) when a drop of dilute hydrochloric acid or strong vinegar is applied. It is found worldwide in sedimentary basins.