sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Tan, gray, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None but breaks easily; Specific Gravity: 2.3 to 2.7.

Hardness: 3 on Mohs scale
Color: Tan, gray, or white
Luster: Dull to earthy

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Tan, gray, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None but breaks easily; 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 lake or ocean water.

Uses & applications

Used extensively in construction (road base, concrete), as a flux in steel making, in the production of lime, as a soil conditioner in agriculture, and as a decorative building stone.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, resulting in spectacular caves and sinkholes.

Field identification & locations

Identify in the field by its soft nature (can be scratched by a knife) and its strong effervescense (fizzing) when in contact with dilute hydrochloric acid. It often contains visible fossils.