Epidote Spectra.

Fig.1. Conoscopic image of a section parallel to Y axis in an epidote crystal. The section is nearly normal to an optic axis.

Fig.2. Same section rotated by 90°. The optic axes angle 2V is close to 90°.

Fig. 3. Polarized spectra of the section described above. Crystal with orientation of figure 1 is Yellow, it gives the b spectrum (red curve). The orientation of figure 2 is green, it gives a mixed spectrum (blue curve). The thickness of this section is 0.4 mm. The spectra in this figure were recorded with an 0.5 mm entrance slit to increase the resolution.

Fig. 4. Section normal to Y axis. It gives the  g spectrum (green) and the  a spectrum (pale yellow). The thickness of the crystal is 0.4 mm.