Iolite: the mineral that's also a compass

Iolite (eye-oh-lite) is a violet-colored gemstone. One of the stone's unique properties is that it changes color from violet to yellow, depending on the angle of incoming sunlight. Iolite was used by Vikings over a thousand years ago to navigate the oceans on overcast days. The gemstone was used as a compass to pinpoint the sun's location through the clouds.

Geologists know the gemstone iolite by its mineral name, cordierite. This mineral is widespread in the rocks of Finland, Norway, Sweden, the Northwest Territories and India.