This chunk of white rock may have been the Viking version of GPS

Every schoolkid learns that the Vikings were kick-ass sailors, and now we may know why. The Alderney crystal, a block of calcite recovered three years ago from a 16th-century shipwreck in the English Channel, has been identified by French and British as a sunstone — thought by some to be mythical. Sunstones were reportedly used by ancient navigators as a compass for cloudy days, determining the position of the obstructed sun by creating a double refraction of sunlight. Icelandic lore has referenced such a "solar stone," though no stone has ever been recovered from the remains of Viking ships or burial sites. Many scholars remain skeptical, but it's pretty obvious the Vikings must have had some edge for all that transatlantic commuting. And we know men never stop and ask for directions. [Source]

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