Crystals may have helped Viking sailors

[Trithemius]

Vikings may have used a special crystal called a sunstone to help navigate the seas even when the sun was obscured by fog or cloud, a study has suggested.

Researchers from Hungary ran a test with sunstones in the Arctic ocean, and found that the crystals can reveal the sun's position even in bad weather.

Link to article (http://news.bbc.co.uk/1/hi/world/europe/6338535.stm)

[Silverfire Darkmoon]

I've heard they did this with iolite. I have no idea how it would have worked.