Bird Dropping

This is from a sample of a bird dropping outside on a fence. The mounting medium has a refractive index of approximately 1.485. There is a single linear polarizing filter in the optical path oriented pependicular to the long axis of the crystal. In this orientation the refractive index is much higher with the calcium oxalate monohydrate crystal that has its alpha refractive index parallel to the long axis and its beta refractive index perpedicular to the long axis.