Sunstone Unearthed From Sixteenth Century Shipwreck

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."

Comments

In a perfect world

[binarylarry]

I hope when it was unearthed the finder said something like "By Odin's Beard! Tis the SUNSTONE that was foretold in the prophecy!"

At least that's what I would have done. 3

Re:In a perfect world

[Nidi62]

This interested the hell out of me, I'd never heard of it before. Wikipedia says it was used to find the sun on a cloudy day, which would indeed be very useful to navigators with no compasses.

I find the timing of this story rather interesting, because the History Channel's newest special miniseries Vikings just started up this past Sunday. In it, the main character reveals to his brother a sunstone that a wanderer had given him. He then proceeds to find the sun through the clouds for his brother, who did not believe that the stone would work.

Prime example of scientific tunnel-vision?

[the biologist]

I hope that by "battery of mechanical and chemical tests", they meant "showed it to a geologist for five minutes". There are a number of minerals which can mimic calcite to the untrained eye, but they're easy for the specialist to distinguish.

Re:Prime example of scientific tunnel-vision?

[Anonymous Coward]

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).

Re:Prime example of scientific tunnel-vision?

[Anonymous Coward]

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.

Re:Prime example of scientific tunnel-vision?

[Anonymous Coward]

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.

Iceland Spar

[kbahey]

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 or the more complex Cordierite, also known as iolite.

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

Viking Sunstone

And here is another:
Viking Compass

Re:Iceland Spar

[An dochasac]

I've done a lot of sailing on the Great Lakes and Irish Sea and I can tell you that cold water often brings a kind of dense low fog. There are times when we can see the tops of masts and blue sky above but because the sun is often low at these latitudes, we can't see where the sun is. But sometimes the fog was so bright, I'd wear sun glasses and then I did notice that the zenith blue sky was polarized. What's more, the digital watch we used for sailing was an LCD watch-- which means it polarized display. And the display did darken noticeably when turned at certain angles, so the reflected sky polarization was also discernible. At the time I wondered whether it could be used as a practical form of navigation, but we had a compass. A few years later Loran-C became popular addition to the compass as and then GPS. But when I heard about the theory that an Iceland spar sunstone might have been used for navigation in the high arctic, I'd give it the nod of plausibility. No it isn't as good as a compass, unless you're above 70 degrees magnetic latitude. No it wouldn't work well under conditions of total cloud cover or rain, might not work at all. But I'm sure this kind of low fog is at least as common in the arctic as it is at my latitude and if I were lost without a compass, GPS, Loran-C on a foggy day, you'd better believe I'd break out the sunstone if I had one.

Re:Iceland Spar

[ScentCone]

also known as iolite

Which, as a man of world, you must know is the source of iocane powder. And because iocane comes from Australia, and Australia is entirely peopled with criminals, and criminals would try to fool wandering Vikings into thinking they could navigate with an iolite stone, we know we cannot trust this story they've put in front of us.

Re:lost knowledge?

[Phrogman]

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.