mineral
Optical Calcite
Calcite (Calcium Carbonate, CaCO3)
Hardness: 3 (Mohs scale), Color: Colorless to pale yellow, Luster: Vitreous, Crystal structure: Trigonal (Rhombohedral cleavage), Specific gravity: 2.71
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Physical properties
Hardness: 3 (Mohs scale), Color: Colorless to pale yellow, Luster: Vitreous, Crystal structure: Trigonal (Rhombohedral cleavage), Specific gravity: 2.71
Formation & geological history
Formed primarily through sedimentary precipitation in marine environments or as a secondary mineral in hydrothermal veins and volcanic cavities. Common in limestone and marble formations of various geological ages.
Uses & applications
Used in the manufacture of high-quality optical instruments, cement, fertilizer, and as a collector specimen. Historically used in navigation and polarizing filters.
Geological facts
Also known as Iceland Spar; it displays strong double refraction (birefringence), meaning an object viewed through it appears doubled. It was used by the Vikings for navigation on cloudy days.
Field identification & locations
Identify in the field by its rhombohedral cleavage (tilted cube shape) and its reaction to weak hydrochloric acid (effervescence). Found worldwide, notably in Iceland, Mexico, and the USA.
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