Is Legendary Viking 'Sunstone' Real?

The sunstone is a type of mineral attested in several 13th–14th century written sources in Iceland, one of which describes its use to locate the sun in a completely overcast sky. A theory exists that the sunstone had polarizing attributes and was used as a navigation instrument by seafarers in the Viking Age.

Though none of these sunstones have 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 amongst the wreckage of the Alderney, an Elizabethan warship that sank near the Channel Islands in 1592.