sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, tan, or bluish-grey; Luster: Dull to earthy; Texture: Fine-grained to clastic; Reaction: Effervesces vigorously with dilute hydrochloric acid.

Hardness: 3 on Mohs scale
Color: Grey, tan, or bluish-grey
Luster: Dull to earthy

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, tan, or bluish-grey; Luster: Dull to earthy; Texture: Fine-grained to clastic; Reaction: Effervesces vigorously with dilute hydrochloric acid.

Formation & geological history

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

Uses & applications

Used extensively as a building stone, in the production of cement, as a soil conditioner in agriculture, and as a raw material in the chemical industry.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, resulting in spectacular cave systems and sinkholes.

Field identification & locations

Identify in the field by its softness (can be scratched by a steel nail) and its reaction to acid. Look for visible fossils or a crystalline structure. Common in areas with ancient seafloods.