sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.3–2.7

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

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None; 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. Formation occurs across all geological eras.

Uses & applications

Extensively used in construction as an aggregate, an ingredient in cement, a soil conditioner in agriculture, and a base material for roads.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in which most caves are formed through the dissolution of calcium carbonate by slightly acidic groundwater.

Field identification & locations

Identify in the field by its reaction to dilute hydrochloric acid (it will fizz/effervesce). Look for fossils or a fine-grained, 'muddy' texture. Commonly found in areas that were once ancient sea beds.