Iolite is sometimes referred to as the 'Viking's Compass' due to its ability to determine the direction of the sun. Legendary Viking explorers, such as Leif Eriksson, were said to have taken pieces of Iolite with them to help navigate the open seas of the Atlantic Ocean and beyond.
While historians are not 100% sure that Iolite was the gemstone used by the ancient Vikings, it seems to be one of the most likely candidates.
It is believed that the ship’s navigator would place a piece of Iolite on a pedestal on the ship’s deck. He would then stand behind the gem, staring at it for his watch. As the ship veered off-course, the navigator would notice slightly different colors in the Iolite as the sunlight entered the gem through a different axis.
The property that made the Iolite change color is its pleochroism, the ability to absorb different wavelengths of light depending upon its crystallographic orientation. A cube cut from Iolite will look violet-blue from one angle, almost like Sapphire, and can be essentially colorless from another angle, and a yellowish-blue from on top. In the past, this property led some people to call Iolite the 'water Sapphire'.
Historians also believe that Iolite helped the Vikings locate the hidden sun. This theory was first proposed by a Danish archaeologist, Thorkild Ramskou. In fact, it was Ramskou who coined the term 'Viking Compass'. While reading the Sagas and other Viking texts, he found a number of references to a Viking 'Sunstone' used for navigation. Ramskou’s theories were based on a combination of what he read in the text and his existing knowledge of an instrument used by SAS trans-arctic pilots for navigation referred to as the Twilight Compass.
When cut thinly, Iolite will also act just like a polarising filter on a camera. It has the ability to remove mist and haze, so it could have been used by Vikings to accurately pinpoint the sun’s location on a cloudy day. If this is indeed true, this intensely colored blue gemstone had two totally different navigational purposes.
Pleochroism may have been helpful in navigation but it certainly makes life difficult for the gem cutter. If Iolite is not cut from exactly the right direction, no matter what the shape of the raw crystal, its color will not be shown to its best advantage. When well cut, Iolite can display a purplish, violet blue – the richer the blue, the better. It can be very similar in color to Tanzanite, but is usually more affordable. It is also harder on the Mohs scale, making it more suitable for daily wear.
Today, Iolite is mined in only a few locations including India, Sri Lanka, Mozambique, Brazil and Zimbabwe. In Viking times, the mining would have probably taken place in Norway and Greenland.
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