sedimentary

Limestone

Limestone (Calcium Carbonate - CaCO3)

Hardness: 3 on Mohs scale; Color: Tan, beige, or yellowish-white; Luster: Dull to earthy; Structure: Fine-grained, non-crystalline appearance; Cleavage: None (conchoidal to irregular fracture).

Hardness: 3 on Mohs scale
Color: Tan, beige, or yellowish-white
Luster: Dull to earthy

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Tan, beige, or yellowish-white; Luster: Dull to earthy; Structure: Fine-grained, non-crystalline appearance; Cleavage: None (conchoidal to irregular fracture).

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also form through chemical precipitation from lake or ocean water. Significant deposits date back to the Paleozoic and Mesozoic eras.

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 like toothpaste or paints.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves are formed in limestone because it is easily dissolved by slightly acidic groundwater.

Field identification & locations

Identify in the field by its softness (can be scratched by a penny) and its reaction to cold dilute hydrochloric acid (it will fizz). Commonly found in areas that were once prehistoric seafloors.