sedimentary

Limestone

Calcium Carbonate (CaCO3) / Limestone

Hardness: 3 on Mohs scale; Color: Gray, light brown, tan, off-white; Luster: Dull to earthy; Crystal Structure: Trigonal (calcite matrix); Cleavage: Perfect rhombohedral in calcite grains; Specific Gravity: ~2.5-2.7

Hardness: 3 on Mohs scale
Color: Gray, light brown, tan, off-white
Luster: Dull to earthy

Identified July 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed predominantly in clear, warm, shallow marine waters through the accumulation and compaction of organic debris such as shell fragments, coral reef material, and chemical precipitation of calcium carbonate over millions of years.

Uses & applications

Extensively used in construction, road base, crushed stone for aggregate, cement and lime production, soil acidity regulation in agriculture, and as a dimension stone in architecture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks worldwide. Large karst landscapes, complete with caves and sinkholes, are formed by the dissolution of limestone by acidic rainwater.

Field identification & locations

Identified easily in the field by its effervescent reaction (fizzing) when exposed to cold dilute hydrochloric acid or strong household vinegar. Found abundantly in ancient sea beds and sedimentary rock formations worldwide.