sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71

Hardness: 3 on Mohs scale
Color: typically gray, tan, or white
Luster: dull to earthy

Identified March 11, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from calcium-rich waters. It scales across all geological ages from Precambrian to Holocene.

Uses & applications

Extensively used in construction as aggregate, in cement manufacturing, as a soil conditioner in agriculture, and as a flux in steel making. Higher purity forms are used in paper, paint, and plastic production.

Geological facts

Limestone occupies about 10% of the total volume of all sedimentary rocks on Earth. Most of the world's great cave systems are carved into limestone via the dissolution of the rock by acidic groundwater.

Field identification & locations

Identified in the field by its softness (can be scratched by a copper coin) and its immediate effervescence (bubbling) when a drop of dilute hydrochloric acid is applied. Commonly found in former sea beds and mountain ranges.