sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: light gray to tan, Luster: dull to earthy, Crystal Structure: Trigonal (as calcite), Cleavage: Rhombohedral (microscopic), Specific Gravity: 2.3-2.7

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale), Color: light gray to tan, Luster: dull to earthy, Crystal Structure: Trigonal (as calcite), Cleavage: Rhombohedral (microscopic), Specific Gravity: 2.3-2.7

Formation & geological history

Formed in warm, shallow marine waters through the accumulation of shell, coral, algal, and fecal debris; also via chemical precipitation from calcium-rich waters.

Uses & applications

Extensively used in construction, road base, manufacturing of cement, lime, and as a soil conditioner in agriculture.

Geological facts

Limestone covers about 10% of the Earth's total land surface and is the primary rock type in which most of the world's caves and karst landscapes are formed.

Field identification & locations

Can be identified in the field by its effervescence (fizzing) when a drop of diluted hydrochloric acid is applied; it often contains visible fossils and is common in sedimentary basins.