Picture of a hornblende crystal in thin section showing the
pleochroism from green to blue to yellow depending on the section
orientation. The two images were photographed with a polarizer rotation by
an angle of 90°.
After rotation of the polarizer, the section changes its
Spectra of the blue and yellow-green sections. The large
band in the visible spectrum of hornblende is attributed to a charge
transfer between Fe++ and Fe+++. The position of this band is orientation
dependant so the observed pleochroism. Two small additional spin forbidden
bands are also visible at lower wavelengths.