sedimentary

Limestone

Calcium Carbonate (CaCO3)

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

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

Identified May 31, 2026More sedimentary →

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Physical properties

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

Formation & geological history

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

Uses & applications

Extensively used in construction as aggregate for road base and railroad ballast, in the manufacturing of cement, as a soil conditioner in agriculture, and as a primary source of lime.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary material found in famous karst landscapes like the Guilin region in China and the cenotes of Mexico.

Field identification & locations

Identify in the field by its softness (can be scratched by a copper coin) and its vigorous reaction (fizzing) when exposed to a drop of diluted hydrochloric acid. Common in ancient sea beds.