sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: Light gray to tan/beige; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5-2.7

Hardness: 3 (Mohs scale)
Color: Light gray to tan/beige
Luster: Dull to earthy

Identified June 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water. Found in vast sedimentary basins globally.

Uses & applications

Extensively used in construction as an aggregate for road base and concrete, as a flux in steel making, in the production of cement and lime, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary component of most of the world's most spectacular caves, which are formed when slightly acidic groundwater dissolves the rock.

Field identification & locations

Identified by its reaction to dilute hydrochloric acid (it will fizz). Often contains visible marine fossils. Commonly found in areas that were once prehistoric seafloors.