First evidence of Viking-like 'sunstone' pulled from shipwreck

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http://science.nbcnews.com/_news/2013/03/07/17226474-first-evidence-of-viking-like-sunstone-pulled-from-shipwreck?lite \

by Megan Ganno
Mar. 7, 2013

Ancient lore has suggested that the Vikings used special crystals to find their way under less-than-sunny skies. Though none of these so-called "sunstones" has ever been found at Viking archaeological sites, a crystal uncovered in a British shipwreck could help prove they did indeed exist.

The crystal was found in the wreckage of the Alderney, an Elizabethan warship that sank near the Channel Islands in 1592. The stone was discovered less than 3 feet (1 meter) from a pair of navigation dividers, suggesting it may have been kept with the ship's other navigational tools, according to the research team headed by scientists at the University of Rennes in France.

A chemical analysis confirmed that the stone was Icelandic Spar, or calcite crystal, believed to be the Vikings' mineral of choice for their fabled sunstones, mentioned in the 13th-century Viking saga of Saint Olaf.

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Because of the rhombohedral shape of calcite crystals, "they refract or polarize light in such a way to create a double image," Mike Harrison, coordinator of the Alderney Maritime Trust, told LiveScience. This means that if you were to look at someone's face through a clear chunk of Icelandic spar, you would see two faces. But if the crystal is held in just the right position, the double image becomes a single image and you know the crystal is pointing east-west, Harrison said.

These refractive powers remain even in low light when it's foggy or cloudy or when twilight has come. In a previous study, the researchers proved they could use Icelandic spar to orient themselves within a few degrees of the sun, even after the sun had dipped below the horizon.

European seafarers had not fully figured out magnetic compasses for navigation until the end of 16th century. The researchers say the crystal might have been used on board the Elizabethan ship to help correct for errors with a magnetic compass.

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