sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, beige, or off-white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline in this form); Cleavage: None in massive form; Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: Grey, beige, or off-white
Luster: Dull to earthy

Identified June 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also be formed by the 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. 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. Many famous landmarks, such as the Great Pyramids of Giza, are constructed from limestone.

Field identification & locations

Can be identified in the field by its softness (scratched by a copper coin) and its effervescence (fizzing) when in contact with cold dilute hydrochloric acid. Commonly found in areas with ancient seabed exposure.