sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

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

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

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, white, buff, or tan; 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 warm, shallow marine waters. It can also form through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as an aggregate for road bases, a raw material for cement/lime, and as a building stone. Also used as a soil conditioner and in glass manufacturing.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves are formed by the dissolution of limestone by slightly acidic groundwater.

Field identification & locations

Identify in the field by testing with a drop of vinegar or weak acid (it will fizz/effervesce). Look for fossils or a gritty, sandy texture. Common in regions that were once ancient seabeds.