Laboratory spectra of amorphous and crystalline olivine: An application to comet Halley IR spectrum

Among the various silicates proposed as components of cosmic dust grains, olivine is considered one of the most likely materials. In this work we present the infrared spectra of three different types of olivine grains: crystalline, amorphous, and synthetic (also amorphous). While the first and second sample derive from the same natural mineral, the third one has been prepared in laboratory according to the relative cosmic abundances of the elements. The experiment data are used to fit the emission feature observed in the comet Halley spectrum between 8 and 13 {mu}m. Satisfactory results are obtained by using synthetic olivine mixed with a small amount (5%) of crystalline grains. 4 refs., 2 figs