mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale. Color: Grayish-white, colorless, or smoky. Lustre: Vitreous to pearly. Crystal system: Trigonal/Rhombohedral. Cleavage: Perfect rhombohedral in three directions. Specific Gravity: 2.71.

Hardness: 3 on Mohs scale
Color: Grayish-white, colorless, or smoky

Identified June 23, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through sedimentary processes including chemical precipitation from groundwater or marine environments, and as a primary mineral in igneous carbonatites or metamorphic marbles.

Uses & applications

Used as a primary component in cement and mortar, in the production of lime, as a soil conditioner in agriculture, and as a flux in steel manufacture. High-clarity specimens are used in optical instruments.

Geological facts

Calcite exhibits double refraction (birefringence); if you place a clear piece over text, it will appear as two images. It is the primary constituent of limestone and marble.

Field identification & locations

Easily identified in the field by its 3-way rhombohedral cleavage and its vigorous effervescence (bubbling) when a drop of dilute hydrochloric acid is applied. Commonly found in sedimentary basins and cave systems.