News of a study that suggests that Vikings may have used crystals to aid in sea navigation on cloudy days. The crystals, called "sunstones", would have allowed them to polarize whatever daylight was available to determine the position of the sun.

"Polarisation cannot be seen with the naked eye, but it can be viewed with what are known as birefringent crystals, or sunstones.

Birefringence, or double refraction, is the splitting of a light wave into two different components - an ordinary and an extraordinary ray.

The researchers found that the crystals could be used to find out where the sun was in the sky in certain foggy or cloudy conditions."

There's something about crystal-gazing Vikings that I find very appealing....