Iolite

 Iolite is the gemstone name for the mineral, cordierite.  The name "iolite" comes from the Greek word for violet. Another old name is dichroite, a Greek word meaning "two-colored rock", a reference to cordierite's strong pleochroism. iolite has also been called "water-sapphire" and "Vikings' Compass" because of its usefulness in determining the direction of the sun on overcast days, the Vikings having used it for this purpose. Iolite is thought to help open upper chakras and aide in communication of spiritual concepts.