sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: Gray, tan, or white with dark weathering; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (in bulk form); Specific gravity: 2.5-2.7

Hardness: 3 (Mohs scale)
Color: Gray, tan, or white with dark weathering
Luster: Dull to earthy

Identified July 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in shallow, warm marine waters 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. It can range in age from hundreds of millions of years to recent deposits.

Uses & applications

Extensively used as building material, road base, an ingredient in cement, a soil conditioner in agriculture, and a flux in steel production. High-grade specimens are used in sculpture and interior architecture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most cave systems are formed in limestone when acidic groundwater dissolves the calcium carbonate.

Field identification & locations

Identify in the field by its soft surface (can be scratched by a steel blade) and its effervescence (bubbling) when exposed to a drop of dilute hydrochloric acid or vinegar. It is commonly found in large bluffs, quarries, and regions with prehistoric marine history.