I just read the following in the April 2012 issue of Popular Science Magazine. I found this quite interesting. Another use for this awesome crystal....low tech.
The Viking Sunstone
1. A
thousand years ago, Vikings navigated with a sunstone, which they used to
locate the sun on cloudy days.
2. The
stone – a calcite crystal called Iceland Spar – funnels light into two
beams. When the beams appear equally
bright, the rock is facing the light, even if it’s obscured.
3. Researchers now use calcite to funnel light
around tiny objects for ‘invisibility’ cloaks.