The Fabled Viking Sunstone*
(also known as Viking Compass)
Iolite (cordierite).

Iolite (cordierite)
Photo courtesy of Gerdus Bronn
The intriguing theory of the Viking's use of a coveted stone to find their way in arctic waters has its roots in the ancient Viking Sagas, optical mineralogy, and in practical application by modern navigators.

Along with exploring the properties of these legendary sunstones, this section pays tribute to the work of the late Leif Karlsen and his wonderfully written and thoroughly researched "Secrets of the Viking Navigators."

*The term "Sunstone" in this paper is from the Nordic languages and refers to the stone as used by the Vikings; "sunstone" in the gem world is a varietal term and can refer to many different minerals, notably in the feldspar family.
The topic of Vikings, Viking navigation and the legend of the Viking Sunstone (also known as "Viking Compass") has been one which has captured my imagination since I was very young when my summers were spent in the historically Viking "rich" area of Vestfold Norway. This is where the famous ships "Oseberg" and "Gokstad" were found and where the ship barrows remain; inspiring dreams of voyages and a life in far distant times. As an adult, journey by sea at the stormy end of Winter in the North Sea from Iceland to the Faeroe Islands and on to Norway, as well as later in a tremendous night time storm in the sea around the Lofoton Islands, made very real the incredible skills of these ancient mariners. For more on the ships, see "The Oseberg,"
part of a wonderful website by Jørn Olav Løset.
Elise on Gaia.

A trip on "Gaia," a replica of the "Gokstad."
Sandefjord, Norway

Photo: E.Skalwold.

Gaia at sail in Sandefjord
Sandefjord, Norway

(YouTube video may not play in Thailand)
Where did this whole idea of a Viking Compass or Sunstone start? First, the terms "Viking Sunstone" and "Viking Compass" are used to mean different things by different authors and they do not always apply to the minerals explored on these pages. Furthermore, the two terms are also both often used to describe the theoretical mineral itself... which could have been several different minerals. I adhere in this writing to Viking "Sunstone" referring to the fabled mineral reported in the Sagas.

As mentioned above, there is also the common use of "sunstone" in English referring to several completely different minerals in the feldspar family and unrelated to this whole theory. In some translations I have found what I believe is a misinterpretation of "Icelandic Spar" calcite ("kalspat", "calkspat" or "calcspar") as "feldspar" ("feltspat") which is then repeated as such in other places, eventually even interpreting it to mean aventurescent feldspar known as sunstone in English - I have even seen the man-made sunstone simulant, "goldstone" glass, pictured as Viking Compass or Sunstone - so one can see where the confusion escalates ("spar" translates to "spat" and visa versa in most Danish and Norwegian dictonaries). Though oligioclase feldspar sunstone is found in Norway, feldspar was never considered as a candidate for the Viking Sunstone; extensive twinning and inclusions would have inhibited its usefulness.

The theory of a mineral used to locate the
hidden sun by the mineral's polarizing optical properties was first put forth by the Danish archeologist, Thorkild Ramskou, who described it in his books Solstenen, Primitiv Navigation i Norden før Kompasset., 1969 and Solkompasset, 1982. He literally coined the expression "Viking Compass" (Vikingernes Kompas) as it is now connected to the mineral cordierite (iolite). The "Sunstone" (Solstenen) is the historical wording referring to such a mineral which he found in the Sagas as well as other texts. Thorkild Ramskou's books are well worth obtaining to appreciate his original thinking on the subject as recorded in his own words without the twisting of time and other purpose.

Though he found these historical references to a sunstone in the Sagas, there was a lack of hard evidence for just how the Vikings might have been able to locate the hidden sun (which would have sometimes been vital to navigation), either as archeological artifacts or detailed direction for their use. Both Ramskou and Leif Karlsen give plausible explanation for this lack and Karlsen later reports the recent finding of a calcite rhomb on a shipwreck of more recent origin.

The notion of the Viking's use of polarized light for navigation was an idea sparked by Ramskou's knowledge of the SAS trans-arctic pilots' use of a polaroid based instrument called the Twilight Compass (Kollsman Sky Compass, Sky Compass or Tusmørke-kompas) to determine the sun's location. He proposed that a local mineral might have been employed in the same way. Both the strong doubling of calcite and extreme pleochroism of various locally found minerals would have been obvious to anyone examining them - a skilled navigator could have easily surmised the implications for use by just gazing through the mineral and turning it various directions. It is just a thought Ramskau jumped on to try to answer his questions... since then it has captured the imaginations of sailors, scientists, history buffs, children, and people smitten with the beauty and lore of gems and minerals.
Click to learn more about the optics of calcite.

Learn more about the optics of calcite.

Click to learn more about the optics of iolite.Click to learn more about the optics of iolite.

Learn more about the optics of iolite.
As a gemologist and educator, I would like to explore the optical properties of the proposed minerals thought to be the fabled Viking "Sunstone" - minerals which are considered gem materials today. This page is intended to provide ancillary material for a seminar I have been writing exploring the science behind the sunstone navigation theory.

There are several candidates for the mineral, among them "Iceland Spar" calcite, a coveted optical quality was found abundantly in Iceland, and iolite, the mineral cordierite found in Norway and popularly known as "Viking's Compass."
The choice of iolite is based on its strong pleochroism which can be used to determine the sun's position; the minerals tourmaline and andalusite have also been suggested for the same reason of strong pleochroism. Thorkild Ramskou favored iolite which is found in various regions of Norway, including Kragerø and Arendal. Repeated experiments with it on a DC-8 flight from Søndre Strømfjord to Copenhagen bore out his theory of its feasibility as a navigational aide..
Leif Karlsen makes a very strong case for Iceland Spar in his book "Secrets of the Viking Navigators." Mr. Karlsen was a professional navigator in the Merchant Marines with, as the title of his book suggests, a fascination for Viking navigation. His proposed technique is premised on the ready availability of optical quality calcite in Iceland which can even be found in the surface scree and which relies on this mineral's high birefringence (see section on calcite optics). Mr. Karlsen devised a plausible scenario as it might have happened more than 1000 years ago and which he found to be extremely accurate.

As a preview, check-out this little YouTube movie on Viking Navigation by NASASciFiles; about 3 minutes into the video there is a demonstration of the Viking Sunstone (in this case, calcite rhomb) just as Karlsen describes it: Viking Sunstone.

Interestingly, "a type of sky compass incorporating Iceland spar was invented by Ch. Wheatstone in 1848 and later improved on by others. Some models are illustrated in one of the series of papers on polarized light published by W. Spottiswoode in Nature ca. 1874, later in book form" (Dr. Leo Kristjansson, personal communication).

Go to The Karlsen section.

Go to the Karlsen section

Leif K. Karlsen's book.

Secrets of the Viking Navigators
by Leif K. Karlsen
Image: One Earth Press.
Bob Skalwold.

Bob Skalwold
In the early 1970's in the company of my father, who also taught navigation and was a long-distance sailor himself, I visited a maritime museum in his family hometown in Norway. There the curator talked about using the so-called sunstone in Viking times for determining the sun's position. He gave us a paper on it which you can read as a pdf "Solsten" - that is, if you read Norwegian - it describes a "semi-precious gemstone" which is used to polarize light to find the hidden location of the sun.
Since that time, my father has also been intrigued by the theory and while I was pursuing my gemological studies, asked me to investigate it further. He had often showed me the effects of polarizing filters and I delighted as a teen in helping him with sextant work while out sailing on Lake Ontario. For those reasons, we are so thrilled with Leif Karlsen's book on the subject..
*In Nordic languages, the Viking stone is called sunstone (Solsten or variants), but this is not to be confused with the many other minerals commonly called "sunstone" many of which are in the feldspar family. These could not possibly be a candidate. If you would like a brief overview of those feldspars, take a look at this as yet unfinished chart.

And, aside from the optics, how does any of this relate to gems? Well, whatever its identity, it was a very valuable possession and warranted mention in the ancient Viking Sagas.... not so diamonds - just to show how status changes.
Sunnmøre Ships.
The Sunnmøre Ships
Photo: E.Skalwold.

Continue to the Leif K. Karlsen Section
Suggested Reading:
  • Barta, A., Horváth, G. and Meyer-Rochow,V.B.(2005) Psychophysical study of the visual sun location in pictures of cloudy and twilight skies inspired by Viking navigation. J. Opt. Soc. Am. A, Vol. 22, No. 6, pp. 1023-1034.
  • Bloss, F.D. (1999) Optical Crystallography. Mineralogical Scociety of America, Washington, D.C. 239 pages.
  • Vebaek, C.L. (1992) The Viking Compass. Gullanders Bogtrykkeri a-s. Skjern, Denmark.
  • Brown, N.M.(2007) The Far Traveller, Voyages of a Viking Woman. Harcourt, Inc. London.306 pages.
  • Burch, D.(2012) Comment on ‘A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight’ By G. Ropars, et al. Proceedings of the Royal Society, Series A (posted August 22, 2012 ) Read Full Text
  • Cohat, Y. (1987) The Vikings Lords of the Seas, R. Daniel, trans. Harry N. Abrams, Inc, London. 175 pages.
  • Crawford, B. E. (1987) Scandinavian Scotland. Leicester University Press. The Bath Press, Avon. 274 pages.
  • Dyar, M.D. and Gunter, M.E. (2007) Mineralogy and Optical Mineralogy. Mineralogical Society of America, Chantilly, Virginia, 708 pages.
  • Gunter, M. (2003). A Luky Break for Polarization: the Optical Properties of Calcite. ExtraLapis English No. 4 Calcite, the Mineral with the Most Forms. Lithographi, East Hampton, CT.pp 40-45.
  • Hawthorne, F.C. and Dirlam, D.M. (2011) Tourmaline the Indicator Mineral: From Atomic Arrangement to Viking Navigation. Elements, Vol. 7, No. 5; pages 307-312.
  • Hegedüs,R., Åkesson,S. and Horváth, G. (2007) Polarization patterns of thick clouds: overcast skies have distribution of the angle of polarization similar to that of clear skies. J. Opt. Soc. Am. A, Vol. 24, No. 8, pp. 2347-2356.
  • Hegedüs R., Åkesson S, Wehner R, HorváthG (2007) Could Vikings have navigated under foggy and cloudy conditions by skylight polarization? On the atmospheric optical prerequisites of polarimetric Viking navigation under foggyand cloudy skies. Proceedings of the Royal Society, Series A4 Vol. 63, pp. 1081-1095.
  • Horváth, G., Barta, A., Pomozi, I., Suhai,B.,Hegedüs R., Åkesson, S., Meyer-Rochow,V.B. and Wehner, R. (2011) On the trail of Vikings with polarizedskylight: experimental study of the atmospheric optical prerequisites allowing polarimetric navigation by Viking seafarers. Philosophical Transactions of the Royal Society B, Vol. 366, 772-782.
  • Jones, G. (1984) A History of the Vikings. Oxford University Press, Oxford. 504 pages.
  • Kristjansson, L. (2002) Iceland Spar: The Helgustadir Calcite Locality and its Influence on the Development of Science. Journal of Geoscience Education, Vol. 50, No. 4, pp. 419-427.
  • Karlsen LK (2000) Secrets of the Viking Navigators. One Earth Press, Seattle,WA. 220 pages.
  • Karlsen LK (2006) Viking navigation using the sunstone, polarized light and the horizon board. Navigator's Newsletter. Starpath School of Navigation, Seattle. Issue 93, Fall. pp 5-8.
  • Magnusson, M. (1980) Vikings! E.P. Dutton, New York. 320 pages.
  • Phillips, W.R.(1971) Mineral Optics, Principles and Techniques. W.H. Freemen and Co. San Francisco. 249 pages.
  • Ramskou, T. (1969) Solstenen: Primitiv Navigation i Norden før Kompassett. Rhodos, København. 96 pages.
  • Ramskou, T. (1982) Solkompasset. Rhodos, København. 68 pages.
  • Ropars,G., Gorre, G., Le Floch,A., Enoch, J., and Lakshminarayanan, V. (2011) A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight. Proceedings of the Royal Society, Series A. 468, 671–684 Full Text Here and please do not miss the Royal Society's later folloy-up publication of Dr. David Burch's Comment which acknowledges Leif Karlsen's earlier publication, "Secrets of the Viking Navigators".
  • Roslund, C.and Beckman. B. (1994) Disputing Viking navigation by polarized skylight. Applied Optics. Vol. 33, No. 21, pp 4754-4755.
  • Sjøvold, T. (1985) The Viking Ships of Oslo. University Oldsaksamling, Oslo. 80 pages.
  • Sturlason, S. (1932) Heimskringla or the Lives of the Norse Kings, Monsen, E., Editor. D.Appleton and Co., New York. 770 pages.
  • Thirslund, S. (1998) Viking Navigation. Gullanders Bogtrykkeri a-s. Skjern, Denmark.
  • Vebaek, C.L. (1992) The Viking Compass. Gullanders Bogtrykkeri a-s. Skjern, Denmark.
  • Wahlgren, E. (1986) The Vikings and America.Thames and Hudson, LTD, London. 192 pages.
  • Wexelsen, E.(ed) (1980) Gokstadfunnet. Sanderfjordmuseene, Sandefjord Norway. 167 pages.
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