sedimentary

Limestone

Limestone (Calcium Carbonate, CaCO3)

Hardness: 3 on Mohs scale; Color: Light gray to white; Luster: Dull or earthy; Structure: Microcrystalline; Cleavage: None (variable fracture); Specific gravity: 2.5-2.7. Reacts with weak acid.

Hardness: 3 on Mohs scale
Color: Light gray to white
Luster: Dull or earthy

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Light gray to white; Luster: Dull or earthy; Structure: Microcrystalline; Cleavage: None (variable fracture); Specific gravity: 2.5-2.7. Reacts with weak acid.

Formation & geological history

Formed primarily in marine environments from the accumulation of coral, shell, and algal debris or by chemical precipitation. Occurs throughout all geological eras, especially the Paleozoic and Mesozoic.

Uses & applications

Used extensively in construction (road base, concrete), agriculture (lime for soil), the steel industry (as a flux), and in the production of glass and cement.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most caves are formed within limestone through the dissolution by acidic groundwater.

Field identification & locations

Identified by its reaction (fizzing) to diluted hydrochloric acid or vinegar. This specimen is a water-worn, rounded pebble commonly found in riverbeds or beaches where limestone outcrops are present.