ROCK TRIVIA; IOLITE
Iolite is called the Viking compass because it is believed that the Vikings used the stone's polarizing filter property to help them find the position of the sun even through clouds or fog.
Iolite has different colors in the different directions in the crystal, the most extreme of any gem, with violet blue on one side, clear or greyish on another and honey from the third. In color, Iolite can be light to dark blue or violet-blue, but it may also occur in light shades of yellow, green, gray, or brown. Violet-blue iolite is considered ideal color.
It is mined in India, Sri Lanka, Mozambique, Zimbabwe, and Brazil. The Vikings probably mined theirs from deposits in Norway and Greenland.
In recent history, gem-quality iolite was found in Palmer Canyon, as well as huge deposits at Grizzly Creek and Ragged Top Mountain Wyoming.
In the picture: One piece from Madagascar, viewed from two different angles that display its pleochroism. The top image shows the specimen from its angle of maximum violet color. The bottom image shows the same specimen rotated by an angle of 90 degrees to show a yellowish color. This specimen is about 4 centimeters in length. Photos by John Sobolewski, displayed here under a Creative Commons license.