## 4 The Example of the Green Stones
### The Fourier Transform InfraRed Spectroscopy (FTIR) Investigation  
The infrared spectrometer uses IR light as a source and is a technique belonging to vibrational spectroscopies. In cultural heritage and archaeometry applications, infrared spectra can help analysts and researchers to identify functional groups that characterize the materials or identify eventual gemstone treatments. Regarding materials characterization, in Table 5, the main vibrational absorption features of the phases discussed in the present work have been reported. Figure 7: micro-Raman spectroscopy—line map tool applied for a green stone characterization, a diopside-quartzite rock, reported as an example of the technique’s feasibility. (**Top-left**) MO image (20\(\times\) magnification, reflected light) showing the mapping area on the sample surface and also the analyses spots; (**Top-right**) data results elaborated by signal to baseline method, considering the two ranges, corresponding to the main vibrational modes of diopside (red line) and quartz (blue line). Note the complementarity of the main bands’ distribution related to the sample area where the signals have been detected, highlighted by the graph; (**bottom**) one of the spot analysis results, corresponding to the cross axes spot in the map image (green): blue and red squares correspond to the quartz and diopside main vibrational mode ranges, used for the elaboration. The map has been carried out using In-Via Confocal micro-Raman Spectroscopy, Renishaw, 514.5 nm source, Wire 5.5 software. Data: [PERSON], GIG. Moreover, Figure 8 shows the absorption spectra of several mineral phases belonging to Green Stones. It is important to note that, different to what has been shown previously for Raman spectroscopy, several bands overlap between the phases, making more complex the identification, especially for minerals belonging to the same groups. This phenomenon is partially correlated with the characteristic broadening of the silicate absorption bands. Moreover, an operative consideration has to be made; the spectra reported in Figure 8 are re-plotted from RRUFF database files [143, 144, 152, 153, 154, 155], collected from a powdered sample in transmission mode. In fact, very high-quality spectra  
Figure 8: Reference IR absorption spectra of several Green Stones samples, re-plotted from RRUFF: Jadeite N. R050220-1 [143], Actinolite N. R040063-1 [144], Pumpellyite N. R070130-1 [153], Diopside N. R040009-1 [152], Antigorite N. R070228-1 [147], and Quartz N. R040031-1 [154]. Powder samples in KBr pellets, transmission mode. Spectra elaboration by Origin 2020 software. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Mineral** & \multicolumn{2}{c}{**Main Vibrations–Wavenumbers (cm\({}^{-1}\))**} & \multicolumn{1}{c}{**References**} \\
**Phase/Variety** & & & & \\ \hline Jadeite & 582 & 999 & 1090 & [122, 141, 142, 143] \\ Nephrite & 686,756 & 950,995 & 1064, 1102 & 3660, 3676 & [122, 123, 141, 144] \\ (Actinolite) & 668,756 & 918, 942, 992 & 1066 & 3675 & [144] \\ (Termolite) & 686,758 & 920, 951, 990 & 1057 & 3673 & [145] \\ Serpentine & 471 & 990 & 1080 & 3671 & [122, 146, 147] \\ (Antigorite) & 449 (-471),617 & 962 & 1084 & 3676 & [146, 147] \\ (Lizardite) & 442,621 & 976 & 1010, 1084 & 3687 & [146] \\ (Chrysotile) & 439,609 & 949 & 1000, 1080 & 3649, 3685 & [146] \\ Albite \({}^{1}\) & 994 & 1040 & & [123, 148] \\ Kosmochlor \({}^{1}\) & 980 & 1114 & & [96] \\ Chromite \({}^{1}\) & 520 b, 650 b & 840, 910 & & [149] \\ Hydrogrossular & & & & & [150] \\ Vesuvariate & 482 & 900, 980 & 1011 & 3570 & [151] \\ Diopside & 456 & 860, 960 & 1065 & & [152] \\ Amphatic & 448,523 & 956 & 1060 & & [122, 126, 142] \\ Pumpellyite & 440 & 947 & & 3406, 3556 & [153] \\ Chalcedony & 450 & 780, 796 & 1067 & & [154] \\ \hline \hline \end{tabular} \({}^{\dagger}\) Several phases constituting Maw-Sit-Sit variety. b = Broad band.  
\end{table} 
Table 5: Infrared main vibrational absorption bands of Green Stones.