Legend tells us that when Viking explorers ventured far out into the Atlantic Ocean, they had a secret gem weapon. 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.