sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: white, tan, or gray; Luster: dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral in calcite crystals but often invisible in rock form; Specific Gravity: 2.7.

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

Identified May 24, 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 chemically through the precipitation of calcium carbonate from lake or ocean water. It ranges from Precambrian to modern times.

Uses & applications

Extensively used as a building material, in the manufacturing of cement, as an aggregate for the base of roads, and as a white pigment or filler in products such as toothpaste or paint. Soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's caves are formed in limestone because it is slightly soluble in rainwater, which becomes naturally acidic.

Field identification & locations

Identified in the field by its softness (can be scratched by a penny) and its reaction to dilute hydrochloric acid (effervescence/bubbles). Commonly found in areas that were once prehistoric shallow seas.