sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs); Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Irregular fracture; Specific gravity: 2.5-2.7

Hardness: 3-4 (Mohs)
Color: Grey, white, or tan
Luster: Dull to earthy

Identified April 14, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs); Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Irregular fracture; Specific gravity: 2.5-2.7

Formation & geological history

Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be precipitate from lake or ocean water (chemical sedimentary rock).

Uses & applications

Used primarily in construction as road base, railroad ballast, and an ingredient in cement. Also used as a soil conditioner and in the manufacture of glass.

Geological facts

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

Field identification & locations

Identify in the field by applying a drop of dilute hydrochloric acid; it will effervesce (fizz). Commonly found in areas that were once ancient sea beds.