sedimentary

Limestone

Calcitic Limestone (CaCO3)

Hardness: 3 (Mohs scale); Color: Whitish-gray to tan; Luster: Dull/Earthy; Structure: Crystalline to microcrystalline; Cleavage: Perfect rhombohedral in calcite crystals, though often massive.

Hardness: 3 (Mohs scale)
Color: Whitish-gray to tan
Luster: Dull/Earthy

Identified July 11, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: Whitish-gray to tan; Luster: Dull/Earthy; Structure: Crystalline to microcrystalline; Cleavage: Perfect rhombohedral in calcite crystals, though often massive.

Formation & geological history

Formed primarily in shallow marine environments 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

Used widely in construction (aggregate, cement, building stone), agriculture (lime for soil), and industrial manufacturing of glass and chemicals.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary component of karst landscapes, leading to the formation of spectacular caves and sinkholes.

Field identification & locations

Can be identified in the field by its softness (can be scratched by a copper coin/steel) and its vigorous effervescence (fizzing) when exposed to a drop of dilute hydrochloric acid. It is found globally in large sedimentary basins.