Global mapping of the nature and distribution of volatiles such as sulfides on Mercury’s surface is essential for understanding the thermal evolution of the planet. The surface exposure of these sulfides over extreme day-night temperature cycles (176 days; 450 degC to -170 degC) on Mercury leads to thermal weathering of these sulfide compounds. It has been seen that among the proposed sulfides on Mercury (MgS, FeS, CaS, CrS, TiS, NaS, and MnS), CaS showed relatively stable and distinctive spectral features in the thermal infrared region (TIR; 7-14 μm) when studied under the simulated Mercury day conditions for temperatures ranging from 100 degC up to 500 degC under vacuum (0.1 mbar) (Varatharajan et al., 2019). In this study, we re-investigated the stability of CaS and its spectral emissivity spectral behavior. We exposed the sample for four consecutive Earth days simulating Mercury day cycles and measured the TIR spectra of CaS for temperatures up to 500 degC (with steps of 100 degC) every day. This time the spectral analysis is coupled and supported by XRD diffraction on the fresh and temperature-processed sample, showing the mineralogical evolution with temperature. We confirm that CaS is a stable compound and therefore it would remain stable on Mercury’s surface regardless of investigated peak surface temperatures. This study further implies that, for the hollows dominated by the sublimation of sulfides on Mercury (Blewett et al., 2013; Helbert et al., 2013a; Vilas et al., 2016), CaS could be the last of the sulfides that could be mapped on Mercury as other sulfides were lost by thermal decomposition, leaving behind hollows. This could make CaS an important tracer for other sulfides, which might be lost in the hollow-forming process and supports the detection of CaS within hollows by MESSENGER (Vilas et al., 2016). The emissivity spectra reported here are significant for the detection and mapping of CaS associated with hollows and pyroclastics using the Mercury Radiometer and Thermal Imaging Spectrometer (MERTIS) datasets.