Iceland spar - Wikipedia

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2024-11-22 04:00:06

Iceland spar, formerly called Iceland crystal (Icelandic: silfurberg [ˈsɪlvʏrˌpɛrk] , lit. ' silver-rock ' ) and also called optical calcite, is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light.[ 1] [ 2]

Iceland spar is a colourless, transparent variety of calcium carbonate (CaCO3).[ 3] It crystallizes in the trigonal system, typically forming rhombohedral crystals.[ 4] It has a Mohs hardness of 3 and exhibits double refraction, splitting a ray of light into two rays that travel at different speeds and directions.[ 3] [ 5]

Iceland spar forms in sedimentary environments, mainly limestone and dolomite rocks, but it also forms in hydrothermal veins and evaporite deposits.[ 6] It precipitates from solutions rich in calcium and carbonate ions, influenced by temperature, pressure, and impurities.[ 6] [ 7]

The most common crystal structure of Iceland spar is rhombohedral, but other structures, such as scalenohedral or prismatic, can form depending on formation conditions.[ 8] [ 9] Iceland spar is primarily found in Iceland but can occur in different parts of the world with suitable geological conditions.[ 3] [ 10]