Before the magnetic compass was introduced in the 13th century, Vikings were said to have used a type of crystal known as a "sunstone" to locate the sun, even on cloudy days, or after the sun had set. A study published on the Proceedings of the Royal Society A website reports finding an example of the legendary crystal.
Scientists from the University of Rennes in France examined a crystal found in the wreck of a British ship that sunk off the island of Alderney in 1592.
The crystal is about the size of a pack of cigarettes and was found near other navigational equipment. After a series of mechanical and chemical tests, the French team determined that the Alderman crystal is a calcite and could have been the ship's optical compass.
The crystal was Iceland spar, a type of calcite that diffracts light into two rays. When you rotate the crystal, the point where the two beams converge indicates the direction of the sun.
They concluded they had found physical evidence of the existence of the Viking’s legendary sunstone. Some scientists remain skeptical, however.
There is only sketchy reference to sunstones in Viking legends, and in any case the shipwreck dated well after the Viking height of the ninth and 10th centuries. But the University of Rennes scientists conjecture that use of sunstones for navigation may have persisted as a back-up to the magnetic compass, which was often unreliable.