sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs), Color: white, cream, or light grey, Luster: earthy to dull, Crystal structure: Trigonal (as calcite), reacts to weak acids

Identified July 20, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs), Color: white, cream, or light grey, Luster: earthy to dull, Crystal structure: Trigonal (as calcite), reacts to weak acids

Formation & geological history

Formed in warm, shallow marine waters through the accumulation of shell, coral, algal, and fecal debris. Can also form through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used primarily in building construction as aggregate, in the manufacture of cement, as a soil conditioner in agriculture, and as a filler in products like paper and toothpaste.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type that contains caves, formed by the dissolution of the rock by acidic groundwater.

Field identification & locations

Can be identified in the field by its light color and its effervescence (bubbling) when a drop of 10% hydrochloric acid is applied. Very common in many regions globally.