sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: White, tan, or gray; Luster: Dull to earthy; Crystal Structure: Rhombohedral (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.3–2.7

Hardness: 3 (Mohs scale)
Color: White, tan, or gray
Luster: Dull to earthy

Identified April 3, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: White, tan, or gray; Luster: Dull to earthy; Crystal Structure: Rhombohedral (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.3–2.7

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

Extensively used as a building material, in the manufacturing of cement, as an aggregate for the base of roads, as a white pigment/filler in products like toothpaste or paints, and as a soil conditioner.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Landscapes formed of limestone are known as 'karst' topography, characterized by caves, sinkholes, and underground drainage.

Field identification & locations

Can be identified in the field because it will effervesce (fizz) when a drop of dilute hydrochloric acid (or strong vinegar) is applied. Often contains visible fossils of marine organisms.