This item is the full tutorial by the same authors relating to birefringence, also known as double refraction of light.  It contains an introduction to birefringence and links to several related interactive Java simulations.

This is the full index of resources on polarized light microscopy by the same authors.  It includes basic concepts, microscope configuration, history of the technique and its applications, and full tutorials on optical birefringence and polarization of light.  Also included are links to more than a dozen related interactive Java simulations.

This item is an interactive Java simulation by the same authors on the topic of birefringence.  It simulates a virtual microscope in which users can view a crystal in a full 360-degree rotation to see the effects of this phenomenon.