Legend tells us that when Leif Eriksson and the other legendary Viking explorers ventured far out into the Atlantic Ocean, moving away from any coastline that could help them determine their position, they had a secret gem weapon: iolite. The Viking mariners used thin pieces of iolite as the world’s first polarizing filter. Looking through an iolite lens, they were able to determine the exact position of the sun, and navigate safely to the new world and back.
The property that made iolite so valuable to the Vikings is extreme pleochroism. Iolite has different colors in different directions within the crystal. A cube cut from iolite will look a violet-ish blue almost like sapphire from one side, clear as water from the other, and a honey yellow from the top. This property led some people to call iolite “water sapphire” in the past, a name that is now obsolete.
Although, pleochroism may have been helpful in navigation,it makes things quite difficult for a gem cutter. If iolite is not cut from exactly the right direction, no matter the shape of the rough, its color will not show to its best advantage.