mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, colorless, or pale cream as shown; Luster: vitreous (glassy) to pearly; Crystal structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral in three directions.

Hardness: 3 on Mohs scale
Color: typically white, colorless, or pale cream as shown
Luster: vitreous (glassy) to pearly

Identified July 3, 2026More mineral →

Explore Calcite in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Forms through chemical precipitation in sedimentary environments, hydrothermal veins, or as the main component of metamorphosed limestone (marble). It can form in marine settings from the shells of organisms.

Uses & applications

Used in construction for cement and mortar, in agriculture for soil treatment, as a gemstone (calcite onyx), and in the chemical industry to neutralize acids. Clear specimens are used in optical instruments.

Geological facts

Calcite exhibits a unique property called double refraction; if you place a clear crystal over a line, the line will appear double. It is the primary mineral in limestone and marble.

Field identification & locations

The easiest field test is the acid test: calcite will effervesce (fizz) vigorously when touched with dilute hydrochloric acid. It is also identifiable by its distinct rhombohedral cleavage and relative softness.