Color:
Blue, with gray and slight yellow modifiers due to its trichroic nature

Durability:
Care must be taken. Best for beads and pendants. There is a cleavage plane along which iolite breaks quite easily

Localities:
Brazil, Burma, India, Sri Lanka, Mozambique, and Zimbabwe,
The Vikings probably mined iolite from deposits in Norway and Greenland.

Iolite

Mg₂Al₃O
Magnesium Aluminum Silicate

Iolite (also known as the mineral cordierite), is a magnesium iron alumino-silicate. The name Iolite was derived from the Greek word for violet, "ios". It has also been called water sapphire because it looks very much like a blue sapphire, and was originally and arguably claimed to be used for nautical purposes. The story is told that when Leif Eriksson and the other legendary Viking explorers ventured far out into the Atlantic Ocean, away from any coastline that could help them determine position, they used thin pieces of iolite as the world's first polarizing filter. Looking through an iolite lens, they could determine the exact position of the sun, which allowed them to navigate safely.
These assertions have never been empiracally proven to be accurate or even possible. There are no archaelogical finds of navigational tools which incorporate iolite. Therefore, I view these tales of Vikings and their iolite with skeptism.

The stone is extremely pleochroic, which means it appears different colors depending upon which direction the stone is viewed. Iolite has three pleochroic directions. In one direction, it appears blue, in another bluish gray and in the other grayish yellow. It is being used extensively in jewelry today because it resembles tanzanite but is much less expensive because it is more plentiful.
Iolite was once thought to have the ability to increase one's faith. It is the talisman for people named Irene. Iolite is different colors in different directions in the crystal. A cube cut from iolite will look a violetish blue almost like sapphire from one side, clear as water from the other, and a honey yellow from the top.