sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

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

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

Identified June 11, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also form through the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used extensively in construction as road base, railroad ballast, and an ingredient in cement. It is also used in agriculture to neutralize soil acidity and in the production of lime.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves are formed by the dissolution of limestone by slightly acidic groundwater.

Field identification & locations

Identify in the field by its softness (can be scratched by a steel nail) and its strong effervescence when exposed to a drop of dilute hydrochloric acid. It is commonly found in large bedded deposits.