sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Cream, tan, or light gray; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None in bulk form; Specific gravity: 2.5-2.7

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

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Cream, tan, or light gray; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None in bulk form; Specific gravity: 2.5-2.7

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Can also form through chemical precipitation from spring or ocean water.

Uses & applications

Extensively used in construction as an aggregate for road bases and railroad ballast; used in the manufacture of cement and lime; historically used for sculpture and architecture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in karst landscapes, which often contain extensive cave systems and sinkholes.

Field identification & locations

Identify in the field by its softness (can be scratched by a copper coin) and its effervescence (bubbling) when it comes into contact with even a weak acid like vinegar. Commonly found in areas that were once prehistoric sea beds.