sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal/Microcrystalline; Cleavage: Perfect rhombohedral in calcite crystals; Specific gravity: 2.3–2.7.

Hardness: 3 on Mohs scale
Color: Gray, tan, or white
Luster: Dull to earthy

Identified April 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also be precipitates from calcium carbonate solution in cave systems or ocean water. Significant deposits range from the Paleozoic to Cenozoic eras.

Uses & applications

Used extensively in construction (aggregate, cement manufacture), agriculture (soil conditioner), and chemical industries (steel refining and glass making). High-purity versions are used in pharmaceuticals and cosmetics.

Geological facts

Many limestones are fossiliferous, containing remnants of ancient sea creatures. It is the primary stone used in the construction of the Great Pyramids of Giza.

Field identification & locations

Identify in the field by applying a drop of dilute hydrochloric acid; it will vigorously effervesce (fizz). It is common in karst landscapes, caves, and mountain ranges. Collectors look for 'fossiliferous limestone' which contains visible fossils.