This is some Indiana Jones level stuff right here. Scientists may have uncovered the Viking "sunstone," a magical-sounding crystal whose powers to locate the sun despite cloud cover, snow, and darkness were understandably considered to be a legend. A group of researchers think a cloudy crystal found in an Elizabethan shipwreck off the Channel Islands may have been the mystical sunstone—thought to be one of the secrets of the Vikings' legendary navigational skills on the seas.
Its appearance in literature have made the sunstone a source of scientific curiosity. A Norse myth describes the stone as a magical gem that could point to the position of the sun before dawn, after sunset, and despite cloud-cover. Viking mythology is riddled with sunstones: in one Icelandic saga, the legendary king Olaf asks his vassal, Sigur, to help him locate the sun on a snowy day. In order to confirm his measurement, "the King made them fetch the solar stone and held it up and saw where light radiated from the stone and thus directly verified Sigur's prediction."
This newly found crystal, cloudy and "cigarette pack-shaped" (modern description, certainly), was found on an English ship. Today, the University of Rennes scientists will publish evidence that the Tudor sailors might have used the stone in a similar way that the Vikings did. No such sunstone has even been discovered before. The failure to discover sunstones could be due to the Viking burial process, which involves cremation of warriors which would have shattered the crystal.
The stone is a calcite substance, known as Iceland spar, which has the ability to create a double refraction of sunlight even when the light was obscured. Use of the stone would require someone to rotate the crystal against their eye until a shadow was formed between the stone and the person; then the sun's position could have been seen through the crystal within a single degree of accuracy. Scientists think that the use of this stone as a navigational could have predated even the compass.