According to Hrafns Saga in the 13th century, the mighty king used a sunstone to navigate in cloudy weather. This is one of several texts that list such artifacts as among the legendary Norse seafaring abilities. New research suggests that the sunstone may be a real navigational tool.
Researchers believe that a mineral called Icelandic Spar, common in Scandanavia, may be the legendary sunstone. Icelandic Spar polarizes light and can be used to detect even a tiny bit of sunlight filtered through clouds. With it you can determine the approximate location of the sun.
The legend of the Viking sunstone got a second look after excavations of a 16th century shipwreck revealed a similar piece of calcite.