sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline calcite); Cleavage: None/Irregular; Specific Gravity: 2.5-2.7

Hardness: 3-4 (Mohs scale)
Color: Gray, tan, or white
Luster: Dull to earthy

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline calcite); Cleavage: None/Irregular; Specific Gravity: 2.5-2.7

Formation & geological history

Formed primarily in shallow, warm marine waters from the accumulation of shell, coral, algal, and fecal debris. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as building stone, road base, and a key ingredient in cement; also used in agriculture to neutralize soil acidity and as a flux in steel making.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It often contains fossils of marine organisms, providing a record of prehistoric sea life.

Field identification & locations

Identified in the field by its softness (can be scratched by a steel nail) and by its vigorous effervescence (bubbling) when in contact with dilute hydrochloric acid or strong vinegar.