sedimentary

Limestone

Calcium carbonate (CaCO3)

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

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

Identified May 1, 2026More sedimentary →

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Physical properties

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

Formation & geological history

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

Uses & applications

Used extensively as a construction material (aggregate), in cement manufacturing, as a soil conditioner in agriculture, and for architectural stone.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It often contains fossils that provide a record of ancient marine life.

Field identification & locations

Identify in the field by its softness (can be scratched with a penny) and vigorous effervescence (fizzing) when a drop of diluted hydrochloric acid or vinegar is applied.