sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: none; Specific Gravity: 2.3 to 2.7

Hardness: 3 on Mohs scale
Color: typically 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: typically grey, white, or tan; 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 marine environments. It can also form through chemical precipitation from ocean or lake water. Formation occurs across all geological ages, notably in the Mississippian and Pennsylvanian periods.

Uses & applications

Extensively used in construction as an aggregate, a key ingredient in cement, a soil conditioner in agriculture, and as a base for many household chemicals and steel production.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in which most of the world's caves are formed through the dissolution by acidic rainwater.

Field identification & locations

Identify in the field by its characteristic grey color and its vigorous reaction (effervescence) when a small amount of dilute hydrochloric acid or vinegar is applied. It is commonly found in ancient seabed deposits.