sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal structure: hexagonal/rhombohedral (microcrystalline calcite); Cleavage: perfect rhombohedral in crystal form; Specific gravity: 2.7.

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

Identified March 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in marine environments by the accumulation of shell, coral, algal, and fecal debris. It can also be formed chemically from the precipitation of calcium carbonate from lake or ocean water. It can range in age from Precambrian to Holocene.

Uses & applications

Extensively used in construction as aggregate, road base, and a component of cement. In industry, it is used for acid neutralization, steel manufacturing, and glass production. Higher grade varieties (marble or decorative limestone) are used in architecture.

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 (caves and sinkholes) develops because it is soluble in slightly acidic water.

Field identification & locations

Identify in the field by applying a drop of dilute hydrochloric acid (or strong vinegar); limestone will effervesce (fizz). Often contains visible fossils of marine organisms. Commonly found in areas that were once prehistoric seafloors.