sedimentary

Limestone

Limestone (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, tan, or off-white; Luster: Dull to earthy; Texture: Fine-grained to clastic; Reacts strongly with dilute hydrochloric acid.

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

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, tan, or off-white; Luster: Dull to earthy; Texture: Fine-grained to clastic; Reacts strongly 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 form through chemical precipitation from ocean or lake water.

Uses & applications

Used extensively in construction as road base, railroad ballast, and a key ingredient in portland cement. Also used as a soil conditioner in agriculture and as a building stone.

Geological facts

Limestone is the primary rock found in karst landscapes, leading to the formation of spectacular caves and sinkholes. Much of the world's oil is stored in limestone reservoirs.

Field identification & locations

Identify in the field by testing with a drop of vinegar or acid (it should fizz). Look for fossil fragments or a fine-grained, chalky texture. Common in areas that were once prehistoric seafloors.