Iceland Spar: the Mineral That Changed Science

Iceland Spar is a clear variety of calcite that exhibits a property known as birefringence: light passing through the crystal is split into two beams, creating a double image. The investigation of this phenomenon led to the discovery of light polarization, which revolutionized multiple fields of science and industry and inspired many technologies still used to this day.

SOURCES:

[Muonium]

Because you are in North America like me, if you got that piece of spar recently and cheaply, it most likely came from Nuevo Leon or Coahuila, Mexico. This means, like the piece sitting on the table in front of me right now, that it's quite likely to be of the so called "Terlingua type calcite" and due to radiation induced crystal lattice defects accumulated over millions of years, thus have another very interesting property associated with it - photoluminescence. If you have access to a good, filtered 365nm longwave UV light, shining it on your sample will likely cause it to fluoresce a pinkish color and induce a second or two of phosphorescence after you turn the light off. If you have access to a shortwave 255nm UV light, it will excite a brilliant unearthly blue fluorescence and long lived phosphorescence that lasts at least 10 seconds in a darkened room.

[fredblonder]

Once again, you’ve made a video on a topic of interest to me. Regarding the Viking Sunstone: I am a member of the Longship Company of Maryland. We own two full-scale Viking ship replicas, and operate them for fun and educational purposes, and occasionally wind up on TV. I have played around with birefringent calcite and found a method that works. First, I place an opaque mark in the center of one face of the crystal. This is difficult because the crystal is slightly slippery, like teflon, so not everything sticks to it. The blue light from the sky is most strongly polarized 90° from the sun. You can easily see this by donning a pair of polarizing glasses and rotating your head while looking at the sky.

Now. picture the scene where the sun is near or just below the horizon, and obscured by clouds or haze, yet there is a patch of blue sky directly overhead. Hold the calcite crystal directly over your head, with the opaque mark on top, and look straight up at the crystal. As you rotate the crystal, the two images of the spot on the far surface will gradually increase and decrease in contrast. When they are of equal intensity, the sun will be directly in line with the fracture plane of the crystal, that is, its side-surface.

There MUST be a small patch of blue sky for this to work, as the light coming through the clouds or haze is diffused and not polarized.

This is the principle used by the Pfund Sky Compass.

And if you want to go off on a really wild tangent, look up the sea-creature known as a Brittle Star. Its skeleton is made of birefringent calcite, and (strangely) the skeleton makes up the lenses of its eyes.

[petergerdes]

Finally, someone explaining things from the history of science that aren't one of the 5 standard stories every damn science popularizer tells. Great work.

[michaelimbesi]

This is amazing! Growing up, one of our neighbors had an interest in geology. We visited their home once and saw their rock collection, and they gave me an interesting souvenir: a clear crystal that I spent the last 18 years convinced was a large single crystal of quartz, although I’d never been able to find another similar piece of quartz. Today, I realized that it is not quartz, because it looks identical to your piece of Iceland Spar, and also produces a double image. Thank you for teaching me something new about a rock that has been decorating my windowsill for years

[whitehat]

I recall a story about the first Scandinavian Airlines commercial polar flights from Copenhagen to Tokyo. Since magnetic compasses are nearly useless on trips in the polar region, all ships and airplanes in that part of the world were commonly equipped with a gyrocompass. The pilot of that Scandinavian Airlines flight, in the spirit of his Viking forefathers, also carried a sunstone as an unofficial experiment. As the plane passed the polar ice cap, he was able to verify that indeed the sunstone worked as reported in the ancient sagas.

[Thomas..Anderson]

5 months and just 12K views. This channel is underappreciated.

[mattwilliams]

I truly love how I can never predict what topic I’ll be learning about when I get a notification that you’ve posted. Bravo as always.

[ehulbert]

Driving across the Borrego Desert east of San Diego a few years ago I came across a bronze plaque that marked a spot where Iceland Spar was mined during the Second World War, it mentioned that the reason the mine was economically viable at the time was because the crystals were exceptionally pure, and that crystals from this mine were used as specified optical elements in Norden Bombsights. During the war, Norden Bombsights were closely guarded secrets. These were given armed military escort when installed and removed from bomber planes, and each one had its own self destruct device. After the war, the mine closed.

[abundantYOUniverse]

Your channel is going to be huge very soon. Congrats you deserve it!

[lohikarhu]

Wow, you have managed to encapsulate a great amount of interesting history, discoveries, and the intersection of many famous names!

[mattbritton]

You got me. Subscribed.

The suit, the French cuffs, the bow tie, the content, just...magnificent.

[UniverseSinking]

Great videos. Very educational. One suggestion: Any way to add the names in writing of the various scientists? That would help people follow along. (As one example, where you say "HAY-guhnz" I think you mean Huygens which is pronounced more like "HOI-gunz" or sometimes like "HIGH-guhnz." Again, great videos & I've subscribed.

[giacatollo]

I'm ashamed to say I judged a book by its cover. You are a great host.

[nicedragon]

You are so interesting and explain everything clearly, logically and are easy to follow and understand. Big applause to you! Now I’ll spread your link to this video to others discussing the Viking sun stone. Thank’s again!

[pepe]

this is top-shelf content. thank you. also +1 for wearing a suit that causes moire patterns in a video about optics. everything about this is fantastic.

[brianmckerrow]

Great for teaching and researching such a format to help other conceptualise fundamental ideas.

[LiborTinka]

One correction: Although Edwin Land discovered the synthesis of quinine, it was Dr. William Bird Herapath who combined quinine with iodine, resulting in light-polarizing crystals. The patent was used by Polaroid to make adjustable glasses. (I took this form one site so please verify this to be sure)

[philipoakley]

Just had a morning fog and checked the polarisation of the fog ("sun in sky" was still visible through the cloud/fog) and did see a little bit of dimming when rotating the polaroid when viewing the fog/cloud at 90 degrees to the sun, to aid the Viking navigation.

It's also worth noting that the Viking were really far north compared to all the USA (except Alaska) viewers. Iceland itself is level with Baffin island (north of Hudson Bay) and the northern half of Alaska, so the sun doesn't get that high in the sky. You could look straight up and use the polariser there to determine the sun angle.

Haars and see-fogs are quite common and not that thick (in altitude), but a real navigation problem.

It's possible that the archaeologists and researchers here in UK & Europe hadn't realised the importance of some small quartz-y like stone among the multiplicity of Viking sites. (I've had a family lunch in the oldest house on Europe on Papa Westray! - so lots of sea borne navigation going on)

[darreno]

Great video, I have played with Iceland Spar but never realised quite how important to science it is. God bless

[noyb]

Anyone using Mussorgsky as intro music to a technical explanation... Great choice.