sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: tan to light brown, Luster: dull to earthy, Crystal structure: Trigonal (as calcite), Cleavage: None visible in hand specimen, Specific gravity: 2.3-2.7

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: tan to light brown, Luster: dull to earthy, Crystal structure: Trigonal (as calcite), Cleavage: None visible in hand specimen, Specific gravity: 2.3-2.7

Formation & geological history

Formed in clear, warm, shallow marine waters from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Widely used in construction (concrete), agriculture (soil treatment), and industrial manufacturing (glass, steel). Also used as a decorative stone and in landscaping.

Geological facts

Limestone covers about 10% of the Earth's land surface. Most of the world's oil and natural gas reservoirs are located in limestone formations, and it is the primary rock type in karst landscapes where caves form.

Field identification & locations

Can be identified in the field by its softness (can be scratched by a copper coin) and its vigorous reaction (fizzing) when a drop of dilute hydrochloric acid or vinegar is applied. Look for it in layered sequences or coastal regions.