Calcite

Physical Properties

Hardness: 3 on Mohs scale; Color: typically white or colorless but can be tinted; Luster: vitreous to pearly; Crystal structure: trigonal (rhombohedral cleavage); Specific gravity: 2.71

Formation & Geological History

Formed through chemical precipitation from calcium-rich solutions or by biological processes in marine environments. Common in sedimentary basins and as a primary mineral in metamorphic marble.

Uses & Applications

Used in the manufacture of cement and mortar, as a soil conditioner in agriculture, as an abrasive, and in the chemical industry. Clear varieties (Iceland Spar) were historically used in optical instruments.

Geological Facts

Calcite is the most stable polymorph of calcium carbonate. It exhibits double refraction, where an object viewed through a clear crystal appears doubled.

Field Identification & Locations

Easily identified in the field by its 3-way rhombohedral cleavage and its vigorous effervescence (bubbling) when treated with cold dilute hydrochloric acid. Commonly found in limestone and marble quarries.

Identified on: 5/2/2026

Mode: Standard