It was used primarily by the Vikings for directions. Nicknames for the stone include, “water sapphire” and “Vikings’ Compass”. Light scattered by air molecules is polarized and in the direction of the polarization is at right angles to the sun, even when the sun is covered by fog or in winter months, sits below the horizon. Iolite occurs in different color variations from sapphire blue to violet, yellow, or light blue depending on the light angle hitting the crystal and more. Iolite is sometimes used as a substitute for sapphire for this reason. It is much softer and more abundant than sapphire, hence less expensive for commercial markets.