Calcite

Physical Properties

Hardness: 3 on Mohs scale; Color: Colorless to white/gray; Luster: Vitreous to pearly; Crystal Structure: Trigonal (rhombohedral habit); Cleavage: Perfect in three directions; Specific Gravity: 2.71

Formation & Geological History

Formed primarily by chemical precipitation in sedimentary environments or as a secondary mineral in igneous cavity infills through hydrothermal activity. Found in marine environments and limestone caves.

Uses & Applications

Used as an abrasive, agricultural soil treatment, construction aggregate, pigment, and in the manufacturing of cement and lime. Large, clear specimens are used in optical instruments.

Geological Facts

Calcite is famous for its double refraction property; if you look through a clear crystal, objects appear doubled. It reacts strongly and effervesces (fizzes) when it comes into contact with dilute hydrochloric acid or vinegar.

Field Identification & Locations

Identify in the field by its rhombohedral cleavage and relative softness (can be scratched by a copper coin). Found globally, with notable deposits in Mexico, Iceland, and the USA. Collectors look for sharp crystal faces and transparency.

Identified on: 4/30/2026

Mode: Standard