sedimentary

Gray Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: Dark gray to bluish-gray, Luster: Dull to earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.5-2.7

Identified June 16, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: Dark gray to bluish-gray, Luster: Dull to earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.5-2.7

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from calcium-rich waters.

Uses & applications

Extensively used in construction as road base, aggregate for concrete, architectural stone, and as a raw material in cement manufacture. Also used in soil conditioning and as a flux in steel making.

Geological facts

Limestone covers about 10% of the total land area of the Earth. Most of our world's oil and natural gas reservoirs are found in porous limestone deposits.

Field identification & locations

Identify by its reaction (fizzing) when exposed to dilute hydrochloric acid. It is often found in massive beds and is a primary component of karst landscapes with caves and sinkholes.