mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale (can be scratched by a copper coin or a knife); Color: Clear, white, or various tints due to impurities; Luster: Vitreous to pearly; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; Specific Gravity: 2.71

Color: Clear, white, or various tints due to impurities
Luster: Vitreous to pearly

Identified January 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 primarily in sedimentary environments through chemical precipitation or as part of biological structures like shells/reefs. It can also form in metamorphic rocks (as marble) or hydrothermal veins. It is found in geological formations spanning from the Precambrian to the present day.

Uses & applications

Extensively used in construction as an ingredient in cement and mortar, as a soil conditioner in agriculture, as a neutralizing agent in the chemical industry, and occasionally as a decorative stone or in jewelry (though limited due to softness).

Geological facts

Calcite exhibits 'double refraction' (birefringence), where light passing through a clear specimen splits into two rays, making objects behind it appear double. It is the primary constituent of limestone and marble.

Field identification & locations

Identify in the field by its perfect rhombohedral cleavage (producing blocky, slanted shapes) and its reaction to weak acid; it will vigorously effervesce (fizz) when a drop of cold dilute hydrochloric acid or vinegar is applied. Common locations include limestone quarries, cave systems (forming stalactites), and hydrothermal mineral veins.