Calcite

Physical Properties

Hardness: 3 on Mohs scale; Color: White/Colorless; Luster: Vitreous to pearly; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; Specific Gravity: 2.71

Formation & Geological History

Formed in sedimentary environments through chemical precipitation or as biogenic remains (shells), or in metamorphic marble and hydrothermal veins. It occurs across all geological ages from Precambrian to modern reef formations.

Uses & Applications

Used in construction as a component of cement and mortar, in agriculture for soil treatment, as a neutralizing agent in the chemical industry, and occasionally as decorative carvings or collector specimens.

Geological Facts

Calcite exhibits a high degree of double refraction; if you place a transparent crystal over text, the letters will appear doubled. It is the primary constituent of limestone and marble.

Field Identification & Locations

Identify in the field by its 3-way rhombohedral cleavage and its vigorous reaction (effervescence) to cold dilute hydrochloric acid. Found globally in limestone quarries and cave environments.

Identified on: 5/2/2026

Mode: Standard