Calcite

Physical Properties

Hardness: 3 on Mohs scale; Color: White/clear with orange/red iron staining; Luster: Vitreous to pearly; Crystal structure: Trigonal/Rhombohedral; Cleavage: Perfect rhombohedral in three directions; Specific gravity: 2.71

Formation & Geological History

Formed through sedimentary processes such as precipitation from marine solutions or as a secondary mineral in igneous and metamorphic rocks. It often forms through the accumulation of shell, coral, and algal debris in marine environments.

Uses & Applications

Used in the manufacturing of cement and mortar, as a soil conditioner in agriculture, a pigment in paint, and high-clarity specimens are used for optical equipment. It is also a popular collector's mineral.

Geological Facts

Calcite is famous for its double refraction (birefringence); when light passes through a clear crystal, it splits into two rays, making objects viewed through it appear doubled. It is the primary component of limestone and marble.

Field Identification & Locations

Identify in the field by its 3-way rhombohedral cleavage and its strong reaction (fizzing) when exposed to dilute hydrochloric acid or vinegar. Common in many geological settings worldwide.

Identified on: 5/2/2026

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