sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (rhombohedral); Specific gravity: 2.5-2.7

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

Identified May 31, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (rhombohedral); Specific gravity: 2.5-2.7

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from ocean water or cave water (stalactites/stalagmites).

Uses & applications

Extensively used in construction as an aggregate, a key component in cement/concrete production, used in soil neutralization for agriculture, and as a flux in steel manufacturing.

Geological facts

Limestone often preserves fossils of ancient marine life. Over long periods under heat and pressure, limestone metamorphoses into marble.

Field identification & locations

Can be identified in the field by its tendency to fizz (effervesce) when a drop of diluted hydrochloric acid or strong vinegar is applied. It is commonly found in large strata across the Midwestern USA and Western Europe.