mineral

Calcite

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale (can be scratched by a copper penny). Color: White, colorless, or yellowish as seen here. Luster: Vitreous to pearly. Crystal Structure: Hexagonal-trigonal. Cleavage: Perfect rhombohedral in three directions.

Hardness: 3 on Mohs scale (can be scratched by a copper penny)
Color: White, colorless, or yellowish as seen here
Luster: Vitreous to pearly

Identified March 29, 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 through chemical precipitation in sedimentary environments, such as marine settings, or as a secondary mineral in igneous and metamorphic rocks. It can also form in hot springs and caves (stalactites/stalagmites).

Uses & applications

Used extensively in construction (as a component of cement and mortar), in the chemical industry for acid neutralization, as an agricultural soil treatment, and occasionally as a gemstone or decorative carving material.

Geological facts

Calcite is famous for its 'double refraction' property; if you place a transparent crystal over text, the text appears doubled. It is the primary constituent of limestone and marble.

Field identification & locations

Identify in the field by its rhombohedral cleavage and its reaction to cold dilute hydrochloric acid (it will fizz/effervesce). It is commonly found in limestone quarries and hydrothermal vein deposits worldwide.