Birefringent materials polarize and split the light into two separate rays that take different paths through the crystal and travel with different speeds. When viewed between crossed polarizers (dark background) they show a colorful display of interference colors that depends on the thickness of the crystal and its orientation. The colors are enhanced by placing a magenta filter in the light path. The crystals were partially dissolved by addition of mineral oil. Field width 1.6 mm.
Image by Eva Johannes, Cellular and Molecular Imaging Facility.