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Science

Sunstone Unearthed From Sixteenth Century Shipwreck 114

Posted by samzenpus
from the guided-by-the-light dept.
sciencehabit writes "In 1592, a British ship sank near the island of Alderney in the English Channel carrying an odd piece of cargo: a small, angular crystal. Once it was brought back to land, a few European scientists began to suspect the mysterious object might be a calcite crystal, a powerful 'sunstone' referred to in Norse legends which they believe Vikings and other European seafarers used to navigate before the introduction of the magnetic compass. Now, after subjecting the object to a battery of mechanical and chemical tests, the team has determined that the Alderman crystal is indeed a calcite and, therefore, could have been the ship's optical compass. Today, similar calcite crystals are used by astronomers to analyze the atmospheres of exoplanets—perhaps setting the stage for a whole new age of exploration."
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Sunstone Unearthed From Sixteenth Century Shipwreck

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  • Iceland Spar (Score:5, Informative)

    by kbahey (102895) on Wednesday March 06, 2013 @09:47PM (#43100769) Homepage

    I read about this a while ago, and it was fascinating. Appartently, the crystals polarized sunlight, even if it was through clouds and

    Here are some links that may help:

    The stone itself is calcite, Iceland Spar [wikipedia.org] or the more complex Cordierite [wikipedia.org], also known as iolite.

    Here is one account of how it could have been used:

    Viking Sunstone [polarization.com]

    And here is another:
    Viking Compass [nordskip.com]

  • by Anonymous Coward on Wednesday March 06, 2013 @10:11PM (#43100923)

    No kidding. 1) it has a hardness of 3 on Mohs hardness scale, 2) it fizzes in acid, 3) it has 3 perfect non-90-degree (rhombohedral) mineral cleavages, etc. Five minutes? More like under one minute. Even the photo is enough to tell that's very probably calcite.

    On the other hand, maybe they needed non-destructive tests, which would make it slightly trickier (hence 5 minutes).

  • by Anonymous Coward on Wednesday March 06, 2013 @11:26PM (#43101363)

    Actually, according to the abstract, they were trying to determine what happened to the crystal while it sat on the seafloor. Alteration from 400+ years of contact with seawater (plus sand abrasion) changed the physical and optical properties somewhat.

  • by Anonymous Coward on Thursday March 07, 2013 @01:10AM (#43101899)

    As it happens, I'm a geologist. There's a difference between alteration and erosion. What the article refers to is the exchange of calcium and magnesium between the crystal and seawater (ratios of Ca and Mg move towards equilibrium with the ocean chemistry). That kind of substitution does change your unit cell a bit; which will alter the properties slightly. It would still be calcite (which is ridiculously easy to identify, as you say); just not quite the same calcite it was before it was dunked.

    Reading the summary, it sounds like the calcite had been altered to the point where it couldn't be used as a sunstone (cloudy and scratched). The tests were to determine if the crystal would have made a good sunstone prior to being soaked/abraded.

  • Re:lost knowledge? (Score:5, Informative)

    by Phrogman (80473) on Thursday March 07, 2013 @02:50AM (#43102267) Homepage

    Its worth noting that while we know the Vikings for their raiding and pillaging, they were in fact some of the most successful traders in Europe at the time. They were also very good and competent craftsmen.
    What we get is the Evil Vikings (tm) version as related by the Christian Church, from when they were (gasp) Pagans and not subject to the rule of that church. Once they had been forced at sword-point to convert to Christianity they became more acceptable. Not that old Norse religion was anything to be particularly happy about mind you. My point is that the Vikings sailed their ships around Europe down into the Mediterranean, conquered Russia (the Rus were effectively Norseman), served as the Imperial Bodyguard for the Byzantine Empire etc. They didn't just destroy and pillage - and most of the other peoples in Europe did a lot of the same thing anyways.
    The Sunstone is a neat idea if true though. I would have bet the Norse navigated mostly by the stars myself, and that they tended to stick to being within sight of land most of the time as most people did prior to the invention of modern navigation.

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