sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Cream, tan, or gray; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (rhombohedral in calcite crystals); Specific Gravity: 2.5–2.7

Hardness: 3 on Mohs scale
Color: Cream, tan, or gray
Luster: Dull to earthy

Identified June 30, 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 through chemical precipitation from ocean water or lakes. Most accessible deposits range from the Paleozoic to Cenozoic eras.

Uses & applications

Major architectural building stone, aggregate for concrete, manufacture of lime and cement, soil conditioner in agriculture, and a source of calcium in animal feed.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is essential for the formation of karst topography, including spectacular cave systems and sinkholes, because it is easily dissolved by acidic groundwater.

Field identification & locations

Can be identified in the field by its reaction to dilute hydrochloric acid (it fizzes). Often contains fossils. Look for it in layered outcrops or quarries in regions with ancient seabed history.