This gem is also known as cordierite, water sapphire and dichroite. The latter alludes to the high level of dichroism, which, apparently, allowed the Vikings to navigate the North Sea in thick fog, as they could determine the sun's position thank to the iolite's property of turning lighter and changing colour, from violet-blue to dun-yellow when turning it in front of a light source. It has a beautiful violet-blue colour, and rarely it appears well crystallized. Besides small pebbled fragments found in the gem-bearing gravels o Sri Lanka and other places, such as Norway, the best specimens come from Madagascar, where they appear in small masses embedded in a schist.