ROCK TRIVIA; IOLITE
Its name comes from the Greek words “ios” for violet and “lithos” for stone. The iolite was also named “dichroite”, the Greek name for “two-colored rock”.
Iolite's nickname, The Viking compass, comes from it's polarizing filter property, which can detect the sun light, even through clouds or fog.
Iolite has different colours in different directions in the crystal. This property is called pleochroism, and Iolite's is the most extreme of any gem, exhibiting violet blue from one side, clear or greyish from the other, and honey yellow from the third.
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.
The picture, courtesy of the GemHunter, is Wyoming Iolite,