Iolite - When Leif Eriksson the legendary Viking explorers ventured into the Atlantic, the Viking mariners used thin pieces of it as the world's first polarizing filter, to determine their position for navigation.
Extreme Pleochroism - is the property which made iolite so valuable to the Vikings. Iolite comes in different colours in different directions in the crystal. An Iolite cube will look violet blue, like Tanzanite from one side, colorless from the other, and a yellow from top. Iolites are extremely difficult to cut- to display the best color, due to the Pleochroism.
Also called Dichroite, Iolite is a blue silicate mineral that occurs as crystals or grains in igneous rocks, only as a result of contamination of the magma by aluminous sediment. When clean, blue iolite is sometimes cut as a gem; the stones from the gem gravels of Sri Lanka have been called water sapphires. Iolite has enjoyed a recent resurgence in popularity due to its affordability and similarity to tanzanite and sapphire at a much lower price.