sedimentary

Limestone

Calcium Carbonate (primarily CaCO3 as Calcite or Aragonite)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: typically off-white, tan, or grey; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: perfect rhombohedral; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: typically off-white, tan, or grey
Luster: dull to earthy

Identified March 28, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically off-white, tan, or grey; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: perfect rhombohedral; Specific Gravity: 2.71

Formation & geological history

Formed primarily in marine environments from the accumulation of skeletal fragments of marine organisms such as coral, foraminifera, and mollusks. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as an aggregate for road bases and railroad ballast, in the production of cement and lime, and as a soil conditioner in agriculture to neutralize acidity.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in which karst topography, featuring caves and sinkholes, develops due to its solubility in slightly acidic rainwater.

Field identification & locations

Can be identified in the field by its softness (scratched by a copper penny or steel) and its strong effervescence (fizzing) when coming into contact with dilute hydrochloric acid or vinegar. Commonly found in quarry sites, riverbeds, and coastal outcroppings.