mineral

Optical Calcite (Iceland Spar)

Calcium Carbonate (CaCO3)

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

Hardness: 3 on Mohs scale
Color: Colorless to white/translucent
Luster: Vitreous to pearly

Identified April 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed through chemical precipitation in sedimentary environments or hydrothermal veins. This specimen displays the double refraction typical of high-purity rhombohedral crystals found in volcanic cavities or limestone deposits.

Uses & applications

Used in the manufacture of high-end optical instruments, polarizing microscopes, and laser technology. Also popular as a metaphysical healing stone and educational specimen.

Geological facts

Famous for its property of double refraction (birefringence), where a single ray of light entering the crystal is split into two rays, causing objects viewed through it to appear doubled. Historically used by Vikings for navigation on cloudy days (the 'Sunstone').

Field identification & locations

Identified in the field by its perfect rhombohedral shape and its reaction (fizzing) to cold dilute hydrochloric acid. Found globally, with notable deposits in Iceland, Mexico, and the USA (New Mexico).

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