I love when it turns out that ancient lore that has been passed down from generation to generation about previous people, early medicine treatments, and science turns out to be true. And it very often is true.
Take the viking sunstones for example. Saint Olaf, in his 13th century saga, told that the Vikings used special crystal to find their way on the seas when it was overcast. It had been presumed to be false since no such stones were ever found in Viking archaeological sites. However, scientists have found several of these extraordinary stones in different parts of the world, such as one that was recently found on a British shipwreck that sank in 1592.
The stone was found among other navigational tools, showing that even in 1592, the stones were still used.
These crystals, confirmed to be Icelandic Spar or calcite crystal, have very unique properties that refracts light to create a double image. That means that if a navigator looked at a person’s face through the crystal, he would see two faces. However, if he held the crystal at just the right angle with the sun, the double image becomes a single image, telling him that he is pointing east-west. Even when cloudy, in low light, fog, or twilight, the crystals remain super accurate – so accurate in fact, that when the magnetic compass was still being refined in the 16th century, the crystal may have been used aboard the ship to correct the compass.