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Iceland spar

Iceland spar, possibly the Icelandic medieval sun stone used to locate the sun in the sky when obstructed from view.[1]

Iceland spar, formerly known as Iceland crystal (Icelandic: silfurberg; lit. silver-rock), is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light (see polarimetry).[2][3] It occurs in large readily cleavable crystals, easily divisible into rhombs, and is remarkable for its double refraction.[4][5]

Historically, the double-refraction property of this crystal was important to understanding the nature of light as a wave. This was studied at length by

  1. ^ a b The Viking Sunstone, from Polarization.net. Retrieved February 8, 2007.
  2. ^  
  3. ^ "Iceland spar".   (Subscription or UK public library membership required.)
  4. ^  This article incorporates text from a publication that is now in the  
  5. ^ Miers, Henry A., Mineralogy: an introduction to the scientific study of minerals. Nabu Press. ISBN 1-177-85127-X Chap. 6, p. 128.
  6. ^  
  7. ^ Nabu Press. ISBN 1-177-14275-9 p. 269.
  8. ^ Whittaker, E. T., A History of the Theories of Aether and Electricity. Dublin University Press, 1910.
  9. ^ Russell, Daniel E . 17 February 2008. Retrieved December 31, 2010. "Helgustadir Iceland Spar Mine" mindat.org
  10. ^ Retrieved January 2, 2011. "Calcite"Granite Gap "Several variety names exist for calcite. Iceland Spar is an ice-clear variety that demonstrates the effect of double refraction or birefringence ... Young mountain ranges in Mexico and South America also host fine localities for calcite. They include Chihuahua, Chihuahua; the Santa Eulalia Dist., Chihuahua; Mapimí, Durango; Guanajuato, Guanajuato; and Charcas, San Luis Potosí; all Mexico"
  11. ^ Kelley, Vincent C. 1940. Retrieved December 31, 2010. "Iceland Spar in Mew Mexico". American Mineralogist, Volume 25, pp. 357-367
  12. ^ WANG Jing-teng, CHEN Hen-shui, YANG En-lin,WU Bo. 2009. Retrieved January 3, 2011. "Geological Characteristics of Iceland Spar Mineral Deposit of Mashan District in Guizhou". China National Knowledge Infrastructure, P619.2 doi:CNKI:SUN:KJQB.0.2009-33-061
  13. ^ Karlsen, Leif K. 2003. Secrets of the Viking Navigators. One Earth Press. ISBN 978-0-9721515-0-4, 220 pp.
  14. ^ Hegedüs, Ramón, Åkesson, Susanne; Wehner, Rüdiger and Horváth, Gábor. 2007. "Could Vikings have navigated under foggy and cloudy conditions by skylight polarization? On the atmospheric optical prerequisites of polarimetric Viking navigation under foggy and cloudy skies". Proc. R. Soc. A 463 (2080): 1081–1095. doi:10.1098/rspa.2007.1811. ISSN 0962-8452.
  15. ^ Ropars, G. et al., 2011. A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science. Available at: http://rspa.royalsocietypublishing.org/content/early/2011/10/28/rspa.2011.0369.abstract [Accessed December 5, 2011].
  16. ^ First evidence of Viking-like 'sunstone' found. Discovery.com. Accessed 11 March 2013.
  17. ^ Greenslade, Thomas B., Jr. "Nicol Prism". Kenyon College. Retrieved 23 January 2014. 

References

William Nicol (1770–1851) invented the first polarizing prism, using Iceland spar to create his Nicol prism.[17]

Nicol prism

It has been speculated that the sunstone (Old Norse: sólarsteinn, a different mineral from the gem-quality sunstone) mentioned in medieval Icelandic texts was Iceland spar, and that Vikings used its light-polarizing property to tell the direction of the sun on cloudy days for navigational purposes.[1][13] The polarization of sunlight in the Arctic can be detected,[14] and the direction of the sun identified to within a few degrees in both cloudy and twilight conditions using the sunstone and the naked eye.[15] The process involves moving the stone across the visual field to reveal a yellow entoptic pattern on the fovea of the eye, probably Haidinger's brush. The recovery of an Iceland spar sunstone from the Elizabethan ship Alderney, which sank in 1592, suggests that this navigational technology may have persisted after the invention of the magnetic compass.[16]

Viking "sunstone"

Mines producing Iceland spar include many mines producing related calcite and aragonite as well as those famously in Iceland,[9] productively in the greater Sonoran desert region as in Santa Eulalia, Chihuahua, Mexico[10] and New Mexico, United States,[11] as well as in the People's Republic of China.[12]

[8] in the 1820s.Augustin-Jean Fresnel Its complete explanation in terms of light polarization was published by [7]

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