mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: White/Honey-Yellow/Colorless, Luster: Vitreous to Pearly, Crystal System: Trigonal, Cleavage: Perfect rhombohedral in 3 directions, Specific Gravity: 2.71

Identified May 12, 2026More mineral →

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Physical properties

Hardness: 3 (Mohs scale), Color: White/Honey-Yellow/Colorless, Luster: Vitreous to Pearly, Crystal System: Trigonal, Cleavage: Perfect rhombohedral in 3 directions, Specific Gravity: 2.71

Formation & geological history

Calcite typically forms as a chemical precipitate from mineral-rich waters or through biological activity (shells and skeletons) in marine environments. It is a major component of sedimentary rocks like limestone and chalk, and metamorphic marble.

Uses & applications

Extensively used in construction (cement and concrete), as a soil acid neutralizer in agriculture, in the optical industry (high-grade clear specimens), and as a calcium supplement. Collectors value unique crystal habits and fluorescent properties.

Geological facts

Calcite exhibits double refraction; if you place a clear piece over a line, you will see two lines. It is also highly reactive to cold dilute hydrochloric acid, which causes it to effervesce or fizz.

Field identification & locations

Identified in the field by its rhombohedral cleavage, its softness (can be scratched by a copper coin but not a fingernail), and its reaction to acid. Commonly found in sedimentary basins and limestone quarries globally.