sedimentary

Limestone

Calcium Carbonate (CaCO3)

Color: Grey to light tan; Hardness: 3 on Mohs scale; Luster: Dull to earthy; Fracture: Conchoidal to irregular; Cleavage: None (though it contains calcite which has rhombohedral cleavage).

Hardness: 3 on Mohs scale
Color: Grey to light tan
Luster: Dull to earthy

Identified June 28, 2026More sedimentary →

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Physical properties

Color: Grey to light tan; Hardness: 3 on Mohs scale; Luster: Dull to earthy; Fracture: Conchoidal to irregular; Cleavage: None (though it contains calcite which has rhombohedral cleavage).

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as an aggregate, a key ingredient in cement, a soil conditioner in agriculture, and as a flux in steel making.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary building block of the Great Pyramids of Giza and many iconic European cathedrals.

Field identification & locations

Can be identified in the field by its tendency to effervesce (fizz) when exposed to a weak acid like vinegar or HCl. Often found in layered beds in mountain ranges or near coastal areas.