sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None visible in hand specimens; Specific gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: Gray, tan, or white
Luster: Dull to earthy

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None visible in hand specimens; Specific gravity: 2.5-2.7

Formation & geological history

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

Uses & applications

Extensively used in construction (aggregate, cement manufacture), agriculture (soil conditioner), and as a industrial raw material for glassmaking and steel refining.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It often contains visible fossils of marine organisms like crinoids or mollusks.

Field identification & locations

Identify in the field by its softness (scratched by a steel knife) and its reaction to dilute hydrochloric acid (it will fizz/effervesce). Found globally in sedimentary basins.