sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, white, or buff; Luster: Dull to earthy; Structure: Microcrystalline; Cleavage: None/Irregular; Specific Gravity: 2.5-2.7

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

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Gray, tan, white, or buff; Luster: Dull to earthy; Structure: Microcrystalline; Cleavage: None/Irregular; Specific Gravity: 2.5-2.7

Formation & geological history

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

Uses & applications

Extensively used in construction as aggregate, road base, and a key ingredient in cement; also used in agriculture to neutralize soil acidity.

Geological facts

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

Field identification & locations

Commonly found in outcrops near ancient ocean beds. Identifiable in the field by its tendency to fizz when exposed to a weak acid (like vinegar) and its relatively soft surface that can be scratched by a steel knife.