sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Irregular; Specific Gravity: 2.5–2.7

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

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Irregular; Specific Gravity: 2.5–2.7

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.

Uses & applications

Used extensively in construction as aggregate, as a base for roads, in the manufacturing of cement, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most cave systems in the world are formed in limestone deposits due to its solubility in acid.

Field identification & locations

Identify in the field by its softness (can be scratched by a steel nail) and its effervescence (bubbling) when in contact with dilute hydrochloric acid. Commonly found in ancient sea beds and riverbanks.