Bronzite Spectra.

Thick section of bronzite from the Sierra Nevada, California (0.25mm thickness) photographed for 2 different orientations of the polarizer (0 and 90). In the visible, only a slight pleochroism can be seen. As shown by the spectra below, the pleochroism of the ortho-pyroxene is very high in the NIR region. The spectra have been recorded for 2 crystals, one yellow and one colorless. The absorption band around 900 nm is produced by the presence of Fe2+ ions in the ortho-pyroxene crystal structure. The onset of the second absorption band of the ortho-pyroxenes (around 2000 nm) can be seen at 1600nm. Due to the InGaAs photodiode used, it is not possible to record the spectra at higher wavelengths to see  the full second band.