Because is it strongly pleochroic, an excellent polarizer, and quite common in Norway, Iolite is the most popular of the minerals speculated for use in determining the location of the sun in an overcast sky. Nobody knows, exactly, how the Vikings managed to sail so precisely across waters far from shore.
As a skylight, iolite can be used to filter light and locate the sun via polarization. This article explains it quite nicely.
Iolite provides us with a lovely blue hue without the price of sapphire. It also displays such strong pleochroism that no special instrumentation is required to observe it. A gem cutter can use this to his or her advantage to orient the table of the gem in such a way to display the best hue available in the stone. As you roll the stone around in your fingers you will see blue, blue-violet, and a yellowish grey.
Ioite jewelry from our fabulously talented Starving Artists:
Featuring artisan handmade creations by the Etsy Starving Artists jewelry team. SATeam members create handcrafted jewelry and beads. More information about our team and its current Etsy shop owner members can be found at SATEAM.etsy.com.