sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: light gray to white; Luster: dull to earthy; Structure: fine-grained/clastic; Cleavage: none; reacts with dilute hydrochloric acid.

Hardness: 3 on Mohs scale
Color: light gray to white
Luster: dull to earthy

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: light gray to white; Luster: dull to earthy; Structure: fine-grained/clastic; Cleavage: none; reacts with dilute hydrochloric acid.

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. 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 an ingredient in cement; also used as a soil conditioner and in the manufacture of glass.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most caves are formed in limestone through the dissolution of the rock by acidic groundwater.

Field identification & locations

Identified in the field by its softness (can be scratched by a steel knife) and its effervescence when exposed to a weak acid. Found globally in areas that were once ancient sea beds.