sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: white, cream, tan, or light gray; Luster: earthy to dull; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71.

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

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: white, cream, tan, or light gray; Luster: earthy to dull; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71.

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments through a process of lithification over millions of years.

Uses & applications

Extensively used in construction, road base, manufacturing of cement and lime, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It is the primary rock found in karst landscapes, leading to the formation of many of the world's largest cave systems.

Field identification & locations

Can be identified in the field by its reaction to cold dilute hydrochloric acid (it fizzes). Common in regions that were once covered by ancient shallow seas. Collectors look for fossil inclusions.