Vikings, and navigation. And rocks.

This was supposed to be a post about the culture shock of living in the boonies of Pennsylvania. But then this showed up in my RSS feeds this morning, and, hell, there's always time later to discuss how weirded out I am to be living in an area where people steal bridges.

Right. So, the vikings. Great seafarers, discovered and settled Iceland and Greenland, poked around in N America before most of Europe knew it existed. All very cool. But there's one thing that most people don't think about. Okay, there's more than one, but there's one that's the real biggie. How did they figure out where they were going?

Being vikings and all, a great deal of their sailing activity was done in or near the Arctic Circle. Which means they did most of their traveling (all they could, I'm sure) in summer. Summer, when, in the Arctic, the sun never goes down. How are you supposed to navigate by the stars, in the Land of the Midnight Sun?

I first encountered this question when I had a job selling crystals and jewelry at a job in Waikiki, years ago. Being me, I was geeking out, researching the history of crystals, and ran into the problem, which historians and tech people have been puzzling over for centuries.

There are references in the Sagas about "A stone with which one could see where the sun was in Heaven." There are mentions of "sun stones" in church inventories, descriptions of gifts (a horse and a sun stone), and other discussions. They were definitely a well-known and valuable (obviously) thing.

But WHAT?

Everyone who knew anything about the situation (rocks, navigation, and history) figured it was probably some kind of feldspar - crystals which, due to their crystalline structure, would polarize light. Moonstone, rainbow moonstone, spectralite, and Labradorite are some of the names used for semi-precious stones used in jewelery that have the effect to some degree or other, hence the pretty reflective qualities of them. (Rainbow moonstones are my personal favorite, for jewelry purposes.) Still, there's a shitload of feldspars out there, and no one was quite sure what in hell the vikings were using.

My choice was always iolite, which I'm not sure is technically a feldspar, now that I think of it, though it has similar diffraction behavior. (I use gem terms for rocks, because I learned about them at a jewelry store rather than in a geology class.) There are clear forms of iolite in a gray-blue that, cut properly, would work exactly like a polarized eyeglass. Check it:

See how it refracts light, and makes the stone look like it's different colors, from different angles? Using one of these would be like finding the sun in the clouds, wearing polarized sunglasses. Which I've done. It would work. The nearest source of iolite for the vikings would have been Cornwall, in the UK. Or Connecticut in N America - but how would they have made it to N America to find the stones, if they hadn't had them first? This is a logistical problem, obviously.

But it appears I was wrong. (SHOCK!)

They discovered an "Icelandic Spar" on a shipwreck that went down in 1592. It so happens that, because they're so freaking common, they're really easy to get hold of, and I actually own one. (What? I'm a geek!) Here it is.

You can see, by the way the light's reflecting off it, that it's got some odd refractive index, and I wasn't even trying. You can also see that it breaks along planes in the crystal structure, which would make shaping it for sunglasses purpose really easy. Probably the deciding feature is, it's so common in Iceland that I've heard people could simply pick them up off the ground at one point. It's been confirmed by scientists who know this stuff that yes, it would work to find the sun on cloudy or bright days.

Solar navigation. With rocks. I love history.

PS: I sold a metric assload of iolite and calcite jewelry to sailors, with this information. Geeks, unite!

ETA: An article from Discover News, with a great photo. Thanks to @sharkgrl for the info!