Famed Viking 'sunstone' found in shipwreck?

Scientists believe an oblong crystal discovered in the wreck of a 16th-century English warship may be the legendary sunstone, a near-mythical device used by Viking mariners to navigate.
The 'sunstone' which was discovered in the wreck of an Elizabethan ship sunk off the Channel Islands has long been the subject of scientific intrigue after it was described in one Icelandic saga as a magical gem which, when held up to sky, would reveal the position of the Sun.
The navigational device could be one of the secrets behind the Vikings' reputation as remarkable seafarers whose prowess at heading into unexplored water might have enabled them to beat Christopher Columbus to discover America by hundreds of years, 'The Independent' reported.

Researchers from the University of Rennes in Brittany suggest Tudor sailors may have used the stone to navigate in much the same way as their Viking predecessors after they studied the cigarette packet-shaped crystal found on board the wreck off Alderney.
The stone - a calcite substance known as Iceland spar - was found by divers next to a pair of dividers, leading investigators to wonder whether it formed part of the navigational arsenal of the English vessel, which sank in 1592, some four years after the Spanish Armada.
Despite the literary references, no intact sunstone has been found on Viking sites.

However, after carrying out several tests, including an analysis to prove its cloudy appearance, the French-led team have concluded that shards of Icelandic spar can act as a remarkably precise navigational aid, the report said.

"Alderney-like crystals could really have been used as an accurate optical sun compass as an aid to ancient navigation," Dr Guy Ropars, writing in the journal Proceedings of the Royal Society, said.
"It permits the observer to follow the azimuth of the sun, far below the horizon with an accuracy as great as plus or minus one degree. The evolution of the Alderney crystal lends hope for identifying other calcite crystals in Viking shipwrecks, burials or settlements," said Ropars.

The principle behind the sunstone relies on its unusual property of creating a double refraction of sunlight, even when it is obscured by cloud or fog of the sort that would have been commonplace for the Vikings, the report said.