Friday, March 22, 2013

Left Side of the Aisle #100 - Part 11

And Another Thing #3: Viking sunstones

Okay, this just is something I think is cool.

The 13th-century Viking saga of Saint Olaf referred to sunstones, special crystals Vikings used, so says the saga, to navigate under less-than-sunny skies. But none have ever been found at a Viking archaeological site, so it was the stuff of speculation and myth.

However, it turns out that a crystal uncovered in the wreck of an Elizabethan warship that sank near the Channel Islands in 1592 could help prove they did indeed exist. The crystal was found less than 3 feet from navigational tools, suggesting it was kept with them. A chemical analysis has confirmed that the stone is Icelandic Spar, or calcite crystal.

The thing is, Icelandic spar is “birefringent,” which means, simply, that if you look through it you'll see a double image, as you may see in the picture. But if the crystal is held in just the right position, the double image becomes a single image and when that happens you know the crystal is pointing east-west. These refractive powers remain even in low light, even when it's foggy, even when it's cloudy, even in twilight, even when the Sun is just below the horizon.

Today, the particular crystal found in the shipwreck would be useless for navigation, because it has been abraded by sand and clouded by magnesium salts. But in good condition, in 1592, especially considering that was a time when European sailors hadn't fully mastered the vagaries of magnetic compasses, the crystal might have been used as a double-check to help correct for errors.

Again, no such crystals have been found yet at Viking sites - which might not be surprising since the Vikings often cremated their dead. But recent excavations have turned up calcite fragments at a Viking settlement, proving some people in the Viking age were employing Iceland spar crystals for something.


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