  In a study to provide ground truth data for mid infrared observations of the
surface of Mercury with the MERTIS (Mercury Radiometer and Thermal Infrared
Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission, we have
studied 17 synthetic glasses. These samples have the chemical compositions of
characteristic Hermean surface areas based on MESSENGER data. The samples have
been characterized using optical microscopy, EMPA and Raman spectroscopy. Mid
infrared spectra have been obtained from polished thin sections using Micro
FTIR, and of powdered size fractions of bulk material (0-25, 25-63, 93-125 and
125-250 micron) in the 2.5 to 18 micron range. The synthetic glasses display
mostly spectra typical for amorphous materials with a dominating, single
Reststrahlen Band (RB) at 9.5 micron to 10.7 micron. RB Features of crystalline
forsterite are found in some cases at 9.5 to 10.2 micron, 10.4 to 11.2 micron,
and at 11.9 micron. Dendritic crystallization starts at a MgO content higher
than 23 wt.% MgO. The Reststrahlen Bands, Christiansen Features (CF), and
Transparency Features (TF) shift depending on the SiO2 and MgO contents. Also a
shift of the Christiansen Feature of the glasses compared with the SCFM
(SiO2/(SiO2+CaO+FeO+MgO)) index is observed. This shift could potentially help
distinguish crystalline and amorphous material in remote sensing data. A
comparison between the degree of polymerization of the glass and the width of
the characteristic strong silicate feature shows a weak positive correlation. A
comparison with a high-quality mid-IR spectrum of Mercury shows some moderate
similarity to the results of this study, but does not explain all features.
