sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Structure: fine-grained to clastic; Cleavage: none (fractures); Specific Gravity: 2.5-2.7

Hardness: 3-4 on Mohs scale
Color: typically gray, tan, or white
Luster: dull to earthy

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 3-4 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Structure: fine-grained to clastic; Cleavage: none (fractures); Specific Gravity: 2.5-2.7

Formation & geological history

Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form via chemical precipitation from ocean water or groundwater. Most deposits range from the Paleozoic to Cenozoic eras.

Uses & applications

Extensively used as a building material, in the manufacture of cement, as an aggregate for road bases, in agricultural lime to neutralize soil acidity, and as a flux in steel making.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary reservoir for most of the world\'s karst topography including vast cave systems.

Field identification & locations

Identify in the field by its reaction (fizzing) with cold dilute hydrochloric acid. Commonly found in areas that were once prehistoric seabeds. Collectors look for fossiliferous limestone containing shells or crinoids.