Iceland spar


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Iceland spar,

colorless variety of crystallized calcitecalcite
, very widely distributed mineral, commonly white or colorless, but appearing in a great variety of colors owing to impurities. Chemically it is calcium carbonate, CaCO3, but it frequently contains manganese, iron, or magnesium in place of the calcium.
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, characterized by its properties of transparency and double refraction. It is used chiefly in the manufacture of Nicol prismsNicol prism
, optical device invented (1828) by William Nicol of Edinburgh. It consists essentially of a crystal of calcite, or Iceland spar, that is cut at an angle into two equal pieces and joined together again with Canada balsam.
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, which are essential parts of polarizing microscopes and other optical instruments. The principal deposit is in Iceland, but small quantities are found in other countries, including the United States and Mexico. Iceland spar is believed by some to have been used by the Vikings as a sunstonesunstone.
1 Crystal mineral thought by some to have been used by the Vikings as an aid to navigation, especially in conditions of low visibility due to clouds or fog when the position of the sun was uncertain.
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Iceland Spar

 

(limestone spar), a variety of the mineral calcite consisting of transparent, colorless, or slightly tinted crystals. It is used in constructing polarizing prisms for various instruments producing polarized light. There is a large deposit near Helgustadir at Eskifjordur in Iceland (hence the name), where optical-quality crystals have been extracted from cavities in basalt. In the USSR deposits of Iceland spar have been found in the Nizhniaia Tunguska Basin, the Yakut and Tuva ASSR’s, the Northern Caucasus, Transcaucasia, Middle Asia, and the Far East.

Iceland spar

[′īs·lənd ′spär]
(mineralogy)
A pure, transparent form of calcite found particularly in Iceland; easily cleaved to form rhombohedral crystals that are doubly refracting. Also known as Iceland crystal.