The Viking Sunstone

The sunstones of the Vikings probably came from Iceland. There the crystal "Island spar" was once easily found if one knew where to look. It is a transparent crystal of calcium-calcite, or crystallized calcium carbonate which occurs in large readily cleavable blocks. It is easily divisible into rhombs, and is remarkable for its double refraction. The Vikings used the light-polarizing property of Iceland spar to point to the direction of the sun on cloudy days, for navigational purposes.

A Viking sunstone is also unique in its shape. Each plane surface meets the adjacent side at specific angle which gives the crystal the apprearance that it is leaning at 11.5 degrees. The sunstone has no right-angle corners. Imagine a clear cube where every angle has been skewed away from the normal 90 degrees - that is the configuration of a sunstone.

Above is a modern crystal of Iceland spar.