Birefringence
Appearance
![](http://178.128.105.246/content-http-upload.wikimedia.org/wikipedia/commons/thumb/7/7a/Calcite.jpg/300px-Calcite.jpg)
Birefringence (or double refraction) happens when light is passed through a special material and it splits into two different rays of light. Calcite crystals and boron nitride are two good examples of materials that cause birefringence. Just as a prism splits light into a large number of colors, birefringence splits light into two images of the same color. You see this as a "double image".
Other websites
[change | change source] Media related to Birefringence at Wikimedia Commons