sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Texture: Fine-grained to clastic; Cleavage: None/Conchoidal or irregular fracture.

Hardness: 3 (Mohs scale)
Color: Gray, tan, or white
Luster: Dull to earthy

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Texture: Fine-grained to clastic; Cleavage: None/Conchoidal or irregular fracture.

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also form through chemical precipitation from calcium-rich water.

Uses & applications

Used extensively as a building material, aggregate for concrete, manufacturing of lime and cement, and in soil conditioning for agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in many of the world's most spectacular cave systems.

Field identification & locations

Can be identified in the field by its softness (it can be scratched by a copper coin) and its energetic reaction (fizzing) when exposed to a drop of dilute hydrochloric acid.