Crystallographic and Mid-Infrared Spectroscopic Properties of the CaS-MgS Solid Solution

We synthesized the solid solution between the sulfides CaS (oldhamite) and MgS (niningerite). Electron microprobe and X-ray diffraction showed homogeneous and pure samples after the synthesis. The calculated lattice parameters fit to earlier literature data. Mid-infrared spectroscopy of the samples reveal that the produced sulfides were fragile and tend to alternate very fast. However, we were able to provide clean reflectance spectra of all samples. The spectra of un-altered samples show no peaks or bands but a rather constant spectrum within the analyzed spectral range between 7.0 and 12.5 μm. The altered spectra contain signatures of sulfates and carbonates and probably further compounds. The gathered data help to understand the formation conditions of the studies sulfides as it shows that the solvus exists in the CaS-MgS system between 1000°C and 1200°C. In addition, the infrared data will help to improve remote sensing in the mid-infrared of planetary objects that might be covered with sulfide containing material like asteroids or Mercury.