mineral

Calcite

Calcium Carbonate (CaCO3)

Mohs hardness of 3, color varies from colorless or white to gray, yellow, green, or pink, vitreous to earthy luster, rhombohedral crystal structure, perfect rhombohedral cleavage, specific gravity of 2.71

Identified July 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed in sedimentary environments through precipitation from water containing dissolved calcium and carbonate ions, also found in metamorphic marble and hydrothermal vein systems across various geological eras

Uses & applications

Used in construction materials (limestone and marble), agriculture to neutralize soil acidity, chemical industry, optical equipment due to birefringence, and as a popular mineral specimen for collectors

Geological facts

Calcite exhibits strong birefringence (double refraction), meaning light passing through it is split into two rays. It is the primary constituent of limestone and marble and reacts strongly with weak acids like hydrochloric acid by fizzing.

Field identification & locations

Easily identified in the field by its characteristic rhombohedral cleavage, softness (easily scratched with a penny), and effervescence when tested with acid. Commonly found worldwide in sedimentary basins, caves as speleothems, and mineral veins.