Effect of anisotropic crystallization on infrared absorption spectra of crystalline silicates

Abstract

Astronomical observation has revealed the presence of crystalline silicates around both evolved and young stars and comets. Circumstellar crystalline silicate grains can be formed by annealing of amorphous grains. Silicate crystals, such as olivine and pyroxene, should grow anisotropically along different crystal axes with different rates.We have performed crystallization experiments of synthetic amorphous silicate materials in laboratory and measured their infrared absorption spectra. By comparison with the spectra with those calculated for crystalline silicate spheroids with different crystallographic orientations, we discuss the effect of anisotropic crystals on their infrared spectra.