Optical Calcite
Calcite var. Iceland Spar · Mineral Specimen / Optical Mineral
Crystal System
Trigonal crystal system; displays a characteristic rhombohedral habit with perfect rhombohedral cleavage.
Mineral Group
Carbonates (Calcite Group)
Chemical Formula
CaCO3
Formation Process
Primarily sedimentary via chemical precipitation or hydrothermal in low-temperature veins and cavities within carbonate-rich rocks.
About This Crystal
Transparent to translucent colorless rhombohedron. Exhibits vitreous luster and distinct internal rainbows caused by light interference on cleavage planes. Displays 'double refraction' (birefringence).
Physical Characteristics
Color: Colorless/White; Streak: White; Cleavage: Perfect rhombohedral in three directions; Fracture: Uneven; Specific Gravity: 2.71; Fluorescence: Often fluoresces red or blue under UV light.
Optical Properties
Extremely high birefringence (RI: 1.486–1.658), causing 'double refraction' where objects viewed through it appear doubled.
Hardness & Durability
Origin Region
Notably from Iceland (historical), Mexico (Chihuahua), Brazil, and the USA (New Mexico). Occurs in hydrothermal veins and limestone cavities.
Hardness & Durability
Mohs hardness of 3. Brittle tenacity; very soft and vulnerable to scratching or cleavage fractures. Not suitable for most jewelry.
Care & Maintenance
Avoid all acids (will effervesce/dissolve). Clean with a soft, dry cloth or mild soapy water. Store separately from harder minerals to prevent scratching.
Rarity & Value
Common mineral, but high-clarity optical grade 'Iceland Spar' is priced higher for collectors and scientific use. Generally affordable.
Special Characteristics
Strong birefringence (double refraction) and internal iridescence (rainbows) resulting from internal cleavage planes reflecting light.
Lore & History
Historically used by Vikings (speculative 'Sunstone') for navigation to locate the sun on cloudy days. Symbolizes clarity and amplification of energy.