sedimentary

Limestone

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull/earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in bulk sample); Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: Grey, tan, or white
Luster: Dull/earthy

Identified May 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. Can also form through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as an aggregate, cement production, architectural stone, soil conditioner in agriculture, and for neutralizing acidic gases.

Geological facts

Limestone is the primary source of the world's lime. It often contains abundant fossils such as crinoids and brachiopods. Many of the world's most famous caves are formed in limestone via dissolution.

Field identification & locations

Identify in the field using the 'acid test'—it fizzes vigorously when exposed to dilute hydrochloric acid. It is often found in bedded layers or massive outcrops in regions that were once ancient sea beds.