sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: White, grey, or tan, Luster: Dull to earthy, Crystal Structure: Trigonal (as calcite), Cleavage: Perfect rhombohedral, Specific Gravity: 2.7

Identified April 25, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: White, grey, or tan, Luster: Dull to earthy, Crystal Structure: Trigonal (as calcite), Cleavage: Perfect rhombohedral, Specific Gravity: 2.7

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from lake or ocean water.

Uses & applications

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

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock found in karst landscapes, which are characterized by caves and sinkholes.

Field identification & locations

Can be identified in the field by its softness (can be scratched by a copper coin) and its strong effervescent reaction to dilute hydrochloric acid. Commonly found in thick beds around the world.