sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, tan, or brownish; Luster: Dull/Earthy; Structure: Fine-grained to clastic; Cleavage: None (conchoidal fracture possible); Specific Gravity: 2.5-2.7.

Hardness: 3 on Mohs scale
Color: Grey, tan, or brownish
Luster: Dull/Earthy

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, tan, or brownish; Luster: Dull/Earthy; Structure: Fine-grained to clastic; Cleavage: None (conchoidal fracture possible); Specific Gravity: 2.5-2.7.

Formation & geological history

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

Uses & applications

Used extensively in construction as road base, concrete aggregate, and building stone. It is also used in the production of cement, steel, 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 source of lime used in making glass and paper. Many of the world's most famous caves, like Mammoth Cave, are carved out of limestone.

Field identification & locations

Identify by its reaction to cold dilute hydrochloric acid (it will fizz/effervesce). It often contains visible fossils. Commonly found in areas that were once prehistoric sea beds.