sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, white, or light yellowish-brown; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals, often indistinct in massive rock; Specific gravity: 2.3 to 2.7.

Hardness: 3 on Mohs scale
Color: Gray, tan, white, or light yellowish-brown
Luster: Dull to earthy

Identified June 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from ocean water or groundwater (travertine). Geological age ranges from Precambrian to present.

Uses & applications

Extensively used in construction as an aggregate, cement production, agriculture for soil neutralization, and as a source for lime (calcium oxide). Some high-quality varieties are used as Dimension Stone.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary parent material for karst topography, which includes caves, sinkholes, and underground drainage systems.

Field identification & locations

Identify in the field using the 'acid test' where it vigorously effervesces (fizzes) when a drop of dilute hydrochloric acid is applied. Commonly found in areas that were once prehistoric seafloors.